xref: /libCEED/interface/ceed-basis.c (revision afeb93e9a539977d805c4dfebb022b4afb833c26)
1 // Copyright (c) 2017-2025, Lawrence Livermore National Security, LLC and other CEED contributors.
2 // All Rights Reserved. See the top-level LICENSE and NOTICE files for details.
3 //
4 // SPDX-License-Identifier: BSD-2-Clause
5 //
6 // This file is part of CEED:  http://github.com/ceed
7 
8 #include <ceed-impl.h>
9 #include <ceed.h>
10 #include <ceed/backend.h>
11 #include <math.h>
12 #include <stdbool.h>
13 #include <stdio.h>
14 #include <string.h>
15 
16 /// @file
17 /// Implementation of CeedBasis interfaces
18 
19 /// @cond DOXYGEN_SKIP
20 static struct CeedBasis_private ceed_basis_none;
21 /// @endcond
22 
23 /// @addtogroup CeedBasisUser
24 /// @{
25 
26 /// Argument for @ref CeedOperatorSetField() indicating that the field does not require a `CeedBasis`
27 const CeedBasis CEED_BASIS_NONE = &ceed_basis_none;
28 
29 /// @}
30 
31 /// ----------------------------------------------------------------------------
32 /// CeedBasis Library Internal Functions
33 /// ----------------------------------------------------------------------------
34 /// @addtogroup CeedBasisDeveloper
35 /// @{
36 
37 /**
38   @brief Compute Chebyshev polynomial values at a point
39 
40   @param[in]  x           Coordinate to evaluate Chebyshev polynomials at
41   @param[in]  n           Number of Chebyshev polynomials to evaluate, `n >= 2`
42   @param[out] chebyshev_x Array of Chebyshev polynomial values
43 
44   @return An error code: 0 - success, otherwise - failure
45 
46   @ref Developer
47 **/
48 static int CeedChebyshevPolynomialsAtPoint(CeedScalar x, CeedInt n, CeedScalar *chebyshev_x) {
49   chebyshev_x[0] = 1.0;
50   chebyshev_x[1] = 2 * x;
51   for (CeedInt i = 2; i < n; i++) chebyshev_x[i] = 2 * x * chebyshev_x[i - 1] - chebyshev_x[i - 2];
52   return CEED_ERROR_SUCCESS;
53 }
54 
55 /**
56   @brief Compute values of the derivative of Chebyshev polynomials at a point
57 
58   @param[in]  x            Coordinate to evaluate derivative of Chebyshev polynomials at
59   @param[in]  n            Number of Chebyshev polynomials to evaluate, `n >= 2`
60   @param[out] chebyshev_dx Array of Chebyshev polynomial derivative values
61 
62   @return An error code: 0 - success, otherwise - failure
63 
64   @ref Developer
65 **/
66 static int CeedChebyshevDerivativeAtPoint(CeedScalar x, CeedInt n, CeedScalar *chebyshev_dx) {
67   CeedScalar chebyshev_x[3];
68 
69   chebyshev_x[1]  = 1.0;
70   chebyshev_x[2]  = 2 * x;
71   chebyshev_dx[0] = 0.0;
72   chebyshev_dx[1] = 2.0;
73   for (CeedInt i = 2; i < n; i++) {
74     chebyshev_x[0]  = chebyshev_x[1];
75     chebyshev_x[1]  = chebyshev_x[2];
76     chebyshev_x[2]  = 2 * x * chebyshev_x[1] - chebyshev_x[0];
77     chebyshev_dx[i] = 2 * x * chebyshev_dx[i - 1] + 2 * chebyshev_x[1] - chebyshev_dx[i - 2];
78   }
79   return CEED_ERROR_SUCCESS;
80 }
81 
82 /**
83   @brief Compute Householder reflection.
84 
85   Computes \f$A = (I - b v v^T) A\f$, where \f$A\f$ is an \f$m \times n\f$ matrix indexed as `A[i*row + j*col]`.
86 
87   @param[in,out] A   Matrix to apply Householder reflection to, in place
88   @param[in]     v   Householder vector
89   @param[in]     b   Scaling factor
90   @param[in]     m   Number of rows in `A`
91   @param[in]     n   Number of columns in `A`
92   @param[in]     row Row stride
93   @param[in]     col Col stride
94 
95   @return An error code: 0 - success, otherwise - failure
96 
97   @ref Developer
98 **/
99 static int CeedHouseholderReflect(CeedScalar *A, const CeedScalar *v, CeedScalar b, CeedInt m, CeedInt n, CeedInt row, CeedInt col) {
100   for (CeedInt j = 0; j < n; j++) {
101     CeedScalar w = A[0 * row + j * col];
102 
103     for (CeedInt i = 1; i < m; i++) w += v[i] * A[i * row + j * col];
104     A[0 * row + j * col] -= b * w;
105     for (CeedInt i = 1; i < m; i++) A[i * row + j * col] -= b * w * v[i];
106   }
107   return CEED_ERROR_SUCCESS;
108 }
109 
110 /**
111   @brief Compute Givens rotation
112 
113   Computes \f$A = G A\f$ (or \f$G^T A\f$ in transpose mode), where \f$A\f$ is an \f$m \times n\f$ matrix indexed as `A[i*n + j*m]`.
114 
115   @param[in,out] A      Row major matrix to apply Givens rotation to, in place
116   @param[in]     c      Cosine factor
117   @param[in]     s      Sine factor
118   @param[in]     t_mode @ref CEED_NOTRANSPOSE to rotate the basis counter-clockwise, which has the effect of rotating columns of `A` clockwise;
119                           @ref CEED_TRANSPOSE for the opposite rotation
120   @param[in]     i      First row/column to apply rotation
121   @param[in]     k      Second row/column to apply rotation
122   @param[in]     m      Number of rows in `A`
123   @param[in]     n      Number of columns in `A`
124 
125   @return An error code: 0 - success, otherwise - failure
126 
127   @ref Developer
128 **/
129 static int CeedGivensRotation(CeedScalar *A, CeedScalar c, CeedScalar s, CeedTransposeMode t_mode, CeedInt i, CeedInt k, CeedInt m, CeedInt n) {
130   CeedInt stride_j = 1, stride_ik = m, num_its = n;
131 
132   if (t_mode == CEED_NOTRANSPOSE) {
133     stride_j  = n;
134     stride_ik = 1;
135     num_its   = m;
136   }
137 
138   // Apply rotation
139   for (CeedInt j = 0; j < num_its; j++) {
140     CeedScalar tau1 = A[i * stride_ik + j * stride_j], tau2 = A[k * stride_ik + j * stride_j];
141 
142     A[i * stride_ik + j * stride_j] = c * tau1 - s * tau2;
143     A[k * stride_ik + j * stride_j] = s * tau1 + c * tau2;
144   }
145   return CEED_ERROR_SUCCESS;
146 }
147 
148 /**
149   @brief View an array stored in a `CeedBasis`
150 
151   @param[in] name   Name of array
152   @param[in] fp_fmt Printing format
153   @param[in] m      Number of rows in array
154   @param[in] n      Number of columns in array
155   @param[in] a      Array to be viewed
156   @param[in] tabs   Tabs to append before each new line
157   @param[in] stream Stream to view to, e.g., `stdout`
158 
159   @return An error code: 0 - success, otherwise - failure
160 
161   @ref Developer
162 **/
163 static int CeedScalarView(const char *name, const char *fp_fmt, CeedInt m, CeedInt n, const CeedScalar *a, const char *tabs, FILE *stream) {
164   if (m > 1) {
165     fprintf(stream, "%s  %s:\n", tabs, name);
166   } else {
167     char padded_name[12];
168 
169     snprintf(padded_name, 11, "%s:", name);
170     fprintf(stream, "%s  %-10s", tabs, padded_name);
171   }
172   for (CeedInt i = 0; i < m; i++) {
173     if (m > 1) fprintf(stream, "%s    [%" CeedInt_FMT "]", tabs, i);
174     for (CeedInt j = 0; j < n; j++) fprintf(stream, fp_fmt, fabs(a[i * n + j]) > 1E-14 ? a[i * n + j] : 0);
175     fputs("\n", stream);
176   }
177   return CEED_ERROR_SUCCESS;
178 }
179 
180 /**
181   @brief Create the interpolation and gradient matrices for projection from the nodes of `basis_from` to the nodes of `basis_to`.
182 
183   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
184   The gradient is given by `grad_project = interp_to^+ * grad_from`, and is only computed for \f$H^1\f$ spaces otherwise it should not be used.
185 
186   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
187 
188   @param[in]  basis_from     `CeedBasis` to project from
189   @param[in]  basis_to       `CeedBasis` to project to
190   @param[out] interp_project Address of the variable where the newly created interpolation matrix will be stored
191   @param[out] grad_project   Address of the variable where the newly created gradient matrix will be stored
192 
193   @return An error code: 0 - success, otherwise - failure
194 
195   @ref Developer
196 **/
197 static int CeedBasisCreateProjectionMatrices(CeedBasis basis_from, CeedBasis basis_to, CeedScalar **interp_project, CeedScalar **grad_project) {
198   bool    are_both_tensor;
199   CeedInt Q, Q_to, Q_from, P_to, P_from;
200 
201   // Check for compatible quadrature spaces
202   CeedCall(CeedBasisGetNumQuadraturePoints(basis_to, &Q_to));
203   CeedCall(CeedBasisGetNumQuadraturePoints(basis_from, &Q_from));
204   CeedCheck(Q_to == Q_from, CeedBasisReturnCeed(basis_to), CEED_ERROR_DIMENSION,
205             "Bases must have compatible quadrature spaces."
206             " 'basis_from' has %" CeedInt_FMT " points and 'basis_to' has %" CeedInt_FMT,
207             Q_from, Q_to);
208   Q = Q_to;
209 
210   // Check for matching tensor or non-tensor
211   {
212     bool is_tensor_to, is_tensor_from;
213 
214     CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
215     CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
216     are_both_tensor = is_tensor_to && is_tensor_from;
217   }
218   if (are_both_tensor) {
219     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_to));
220     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_from));
221     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis_from, &Q));
222   } else {
223     CeedCall(CeedBasisGetNumNodes(basis_to, &P_to));
224     CeedCall(CeedBasisGetNumNodes(basis_from, &P_from));
225   }
226 
227   // Check for matching FE space
228   CeedFESpace fe_space_to, fe_space_from;
229 
230   CeedCall(CeedBasisGetFESpace(basis_to, &fe_space_to));
231   CeedCall(CeedBasisGetFESpace(basis_from, &fe_space_from));
232   CeedCheck(fe_space_to == fe_space_from, CeedBasisReturnCeed(basis_to), CEED_ERROR_MINOR,
233             "Bases must both be the same FE space type."
234             " 'basis_from' is a %s and 'basis_to' is a %s",
235             CeedFESpaces[fe_space_from], CeedFESpaces[fe_space_to]);
236 
237   // Get source matrices
238   CeedInt           dim, q_comp = 1;
239   CeedScalar       *interp_to_inv, *interp_from;
240   const CeedScalar *interp_to_source = NULL, *interp_from_source = NULL, *grad_from_source = NULL;
241 
242   CeedCall(CeedBasisGetDimension(basis_from, &dim));
243   if (are_both_tensor) {
244     CeedCall(CeedBasisGetInterp1D(basis_to, &interp_to_source));
245     CeedCall(CeedBasisGetInterp1D(basis_from, &interp_from_source));
246   } else {
247     CeedCall(CeedBasisGetNumQuadratureComponents(basis_from, CEED_EVAL_INTERP, &q_comp));
248     CeedCall(CeedBasisGetInterp(basis_to, &interp_to_source));
249     CeedCall(CeedBasisGetInterp(basis_from, &interp_from_source));
250   }
251   CeedCall(CeedMalloc(Q * P_from * q_comp, &interp_from));
252   CeedCall(CeedCalloc(P_to * P_from, interp_project));
253 
254   // `grad_project = interp_to^+ * grad_from` is computed for the H^1 space case so the
255   // projection basis will have a gradient operation (allocated even if not H^1 for the
256   // basis construction later on)
257   if (fe_space_to == CEED_FE_SPACE_H1) {
258     if (are_both_tensor) {
259       CeedCall(CeedBasisGetGrad1D(basis_from, &grad_from_source));
260     } else {
261       CeedCall(CeedBasisGetGrad(basis_from, &grad_from_source));
262     }
263   }
264   CeedCall(CeedCalloc(P_to * P_from * (are_both_tensor ? 1 : dim), grad_project));
265 
266   // Compute interp_to^+, pseudoinverse of interp_to
267   CeedCall(CeedCalloc(Q * q_comp * P_to, &interp_to_inv));
268   CeedCall(CeedMatrixPseudoinverse(CeedBasisReturnCeed(basis_to), interp_to_source, Q * q_comp, P_to, interp_to_inv));
269   // Build matrices
270   CeedInt     num_matrices = 1 + (fe_space_to == CEED_FE_SPACE_H1) * (are_both_tensor ? 1 : dim);
271   CeedScalar *input_from[num_matrices], *output_project[num_matrices];
272 
273   input_from[0]     = (CeedScalar *)interp_from_source;
274   output_project[0] = *interp_project;
275   for (CeedInt m = 1; m < num_matrices; m++) {
276     input_from[m]     = (CeedScalar *)&grad_from_source[(m - 1) * Q * P_from];
277     output_project[m] = &((*grad_project)[(m - 1) * P_to * P_from]);
278   }
279   for (CeedInt m = 0; m < num_matrices; m++) {
280     // output_project = interp_to^+ * interp_from
281     memcpy(interp_from, input_from[m], Q * P_from * q_comp * sizeof(input_from[m][0]));
282     CeedCall(CeedMatrixMatrixMultiply(CeedBasisReturnCeed(basis_to), interp_to_inv, input_from[m], output_project[m], P_to, P_from, Q * q_comp));
283     // Round zero to machine precision
284     for (CeedInt i = 0; i < P_to * P_from; i++) {
285       if (fabs(output_project[m][i]) < 10 * CEED_EPSILON) output_project[m][i] = 0.0;
286     }
287   }
288 
289   // Cleanup
290   CeedCall(CeedFree(&interp_to_inv));
291   CeedCall(CeedFree(&interp_from));
292   return CEED_ERROR_SUCCESS;
293 }
294 
295 /**
296   @brief Check input vector dimensions for CeedBasisApply[Add]
297 
298   @param[in]  basis     `CeedBasis` to evaluate
299   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
300                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
301   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
302                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
303   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
304                           @ref CEED_EVAL_INTERP to use interpolated values,
305                           @ref CEED_EVAL_GRAD to use gradients,
306                           @ref CEED_EVAL_DIV to use divergence,
307                           @ref CEED_EVAL_CURL to use curl,
308                           @ref CEED_EVAL_WEIGHT to use quadrature weights
309   @param[in]  u         Input `CeedVector`
310   @param[out] v         Output `CeedVector`
311 
312   @return An error code: 0 - success, otherwise - failure
313 
314   @ref Developer
315 **/
316 static int CeedBasisApplyCheckDims(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
317   CeedInt  dim, num_comp, q_comp, num_nodes, num_qpts;
318   CeedSize u_length = 0, v_length;
319 
320   CeedCall(CeedBasisGetDimension(basis, &dim));
321   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
322   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
323   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
324   CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
325   CeedCall(CeedVectorGetLength(v, &v_length));
326   if (u) CeedCall(CeedVectorGetLength(u, &u_length));
327 
328   // Check vector lengths to prevent out of bounds issues
329   bool has_good_dims = true;
330   switch (eval_mode) {
331     case CEED_EVAL_NONE:
332     case CEED_EVAL_INTERP:
333     case CEED_EVAL_GRAD:
334     case CEED_EVAL_DIV:
335     case CEED_EVAL_CURL:
336       has_good_dims = ((t_mode == CEED_TRANSPOSE && u_length >= (CeedSize)num_elem * (CeedSize)num_comp * (CeedSize)num_qpts * (CeedSize)q_comp &&
337                         v_length >= (CeedSize)num_elem * (CeedSize)num_comp * (CeedSize)num_nodes) ||
338                        (t_mode == CEED_NOTRANSPOSE && v_length >= (CeedSize)num_elem * (CeedSize)num_qpts * (CeedSize)num_comp * (CeedSize)q_comp &&
339                         u_length >= (CeedSize)num_elem * (CeedSize)num_comp * (CeedSize)num_nodes));
340       break;
341     case CEED_EVAL_WEIGHT:
342       has_good_dims = v_length >= (CeedSize)num_elem * (CeedSize)num_qpts;
343       break;
344   }
345   CeedCheck(has_good_dims, CeedBasisReturnCeed(basis), CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
346   return CEED_ERROR_SUCCESS;
347 }
348 
349 /**
350   @brief Check input vector dimensions for CeedBasisApply[Add]AtPoints
351 
352   @param[in]  basis      `CeedBasis` to evaluate
353   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
354                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
355   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
356   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
357                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
358   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
359                            @ref CEED_EVAL_GRAD to use gradients,
360                            @ref CEED_EVAL_WEIGHT to use quadrature weights
361   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
362   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
363   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
364 
365   @return An error code: 0 - success, otherwise - failure
366 
367   @ref Developer
368 **/
369 static int CeedBasisApplyAtPointsCheckDims(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode,
370                                            CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u, CeedVector v) {
371   CeedInt  dim, num_comp, num_q_comp, num_nodes, P_1d = 1, Q_1d = 1, total_num_points = 0;
372   CeedSize x_length = 0, u_length = 0, v_length;
373 
374   CeedCall(CeedBasisGetDimension(basis, &dim));
375   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
376   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
377   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
378   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &num_q_comp));
379   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
380   CeedCall(CeedVectorGetLength(v, &v_length));
381   if (x_ref != CEED_VECTOR_NONE) CeedCall(CeedVectorGetLength(x_ref, &x_length));
382   if (u != CEED_VECTOR_NONE) CeedCall(CeedVectorGetLength(u, &u_length));
383 
384   // Check compatibility coordinates vector
385   for (CeedInt i = 0; i < num_elem; i++) total_num_points += num_points[i];
386   CeedCheck((x_length >= (CeedSize)total_num_points * (CeedSize)dim) || (eval_mode == CEED_EVAL_WEIGHT), CeedBasisReturnCeed(basis),
387             CEED_ERROR_DIMENSION,
388             "Length of reference coordinate vector incompatible with basis dimension and number of points."
389             " Found reference coordinate vector of length %" CeedSize_FMT ", not of length %" CeedSize_FMT ".",
390             x_length, (CeedSize)total_num_points * (CeedSize)dim);
391 
392   // Check CEED_EVAL_WEIGHT only on CEED_NOTRANSPOSE
393   CeedCheck(eval_mode != CEED_EVAL_WEIGHT || t_mode == CEED_NOTRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED,
394             "CEED_EVAL_WEIGHT only supported with CEED_NOTRANSPOSE");
395 
396   // Check vector lengths to prevent out of bounds issues
397   bool has_good_dims = true;
398   switch (eval_mode) {
399     case CEED_EVAL_INTERP:
400       has_good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= (CeedSize)total_num_points * (CeedSize)num_q_comp ||
401                                                      v_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)) ||
402                        (t_mode == CEED_NOTRANSPOSE && (v_length >= (CeedSize)total_num_points * (CeedSize)num_q_comp ||
403                                                        u_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)));
404       break;
405     case CEED_EVAL_GRAD:
406       has_good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= (CeedSize)total_num_points * (CeedSize)num_q_comp * (CeedSize)dim ||
407                                                      v_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)) ||
408                        (t_mode == CEED_NOTRANSPOSE && (v_length >= (CeedSize)total_num_points * (CeedSize)num_q_comp * (CeedSize)dim ||
409                                                        u_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)));
410       break;
411     case CEED_EVAL_WEIGHT:
412       has_good_dims = t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points);
413       break;
414       // LCOV_EXCL_START
415     case CEED_EVAL_NONE:
416     case CEED_EVAL_DIV:
417     case CEED_EVAL_CURL:
418       return CeedError(CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points not supported for %s",
419                        CeedEvalModes[eval_mode]);
420       // LCOV_EXCL_STOP
421   }
422   CeedCheck(has_good_dims, CeedBasisReturnCeed(basis), CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
423   return CEED_ERROR_SUCCESS;
424 }
425 
426 /**
427   @brief Default implimentation to apply basis evaluation from nodes to arbitrary points
428 
429   @param[in]  basis      `CeedBasis` to evaluate
430   @param[in]  apply_add  Sum result into target vector or overwrite
431   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
432                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
433   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
434   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
435                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
436   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
437                            @ref CEED_EVAL_GRAD to use gradients,
438                            @ref CEED_EVAL_WEIGHT to use quadrature weights
439   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
440   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
441   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
442 
443   @return An error code: 0 - success, otherwise - failure
444 
445   @ref Developer
446 **/
447 static int CeedBasisApplyAtPoints_Core(CeedBasis basis, bool apply_add, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode,
448                                        CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u, CeedVector v) {
449   CeedInt dim, num_comp, P_1d = 1, Q_1d = 1, total_num_points = num_points[0];
450 
451   CeedCall(CeedBasisGetDimension(basis, &dim));
452   // Inserting check because clang-tidy doesn't understand this cannot occur
453   CeedCheck(dim > 0, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Malformed CeedBasis, dim > 0 is required");
454   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
455   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
456   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
457 
458   // Default implementation
459   {
460     bool is_tensor_basis;
461 
462     CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
463     CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED,
464               "Evaluation at arbitrary points only supported for tensor product bases");
465   }
466   CeedCheck(num_elem == 1, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED,
467             "Evaluation at arbitrary  points only supported for a single element at a time");
468   if (eval_mode == CEED_EVAL_WEIGHT) {
469     CeedCall(CeedVectorSetValue(v, 1.0));
470     return CEED_ERROR_SUCCESS;
471   }
472   if (!basis->basis_chebyshev) {
473     // Build basis mapping from nodes to Chebyshev coefficients
474     CeedScalar       *chebyshev_interp_1d, *chebyshev_grad_1d, *chebyshev_q_weight_1d;
475     const CeedScalar *q_ref_1d;
476     Ceed              ceed;
477 
478     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_interp_1d));
479     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_grad_1d));
480     CeedCall(CeedCalloc(Q_1d, &chebyshev_q_weight_1d));
481     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
482     CeedCall(CeedBasisGetChebyshevInterp1D(basis, chebyshev_interp_1d));
483 
484     CeedCall(CeedBasisGetCeed(basis, &ceed));
485     CeedCall(CeedVectorCreate(ceed, num_comp * CeedIntPow(Q_1d, dim), &basis->vec_chebyshev));
486     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d, Q_1d, chebyshev_interp_1d, chebyshev_grad_1d, q_ref_1d, chebyshev_q_weight_1d,
487                                      &basis->basis_chebyshev));
488 
489     // Cleanup
490     CeedCall(CeedFree(&chebyshev_interp_1d));
491     CeedCall(CeedFree(&chebyshev_grad_1d));
492     CeedCall(CeedFree(&chebyshev_q_weight_1d));
493     CeedCall(CeedDestroy(&ceed));
494   }
495 
496   // Create TensorContract object if needed, such as a basis from the GPU backends
497   if (!basis->contract) {
498     Ceed      ceed_ref;
499     CeedBasis basis_ref = NULL;
500 
501     CeedCall(CeedInit("/cpu/self", &ceed_ref));
502     // Only need matching tensor contraction dimensions, any type of basis will work
503     CeedCall(CeedBasisCreateTensorH1Lagrange(ceed_ref, dim, num_comp, P_1d, Q_1d, CEED_GAUSS, &basis_ref));
504     // Note - clang-tidy doesn't know basis_ref->contract must be valid here
505     CeedCheck(basis_ref && basis_ref->contract, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED,
506               "Reference CPU ceed failed to create a tensor contraction object");
507     CeedCall(CeedTensorContractReferenceCopy(basis_ref->contract, &basis->contract));
508     CeedCall(CeedBasisDestroy(&basis_ref));
509     CeedCall(CeedDestroy(&ceed_ref));
510   }
511 
512   // Basis evaluation
513   switch (t_mode) {
514     case CEED_NOTRANSPOSE: {
515       // Nodes to arbitrary points
516       CeedScalar       *v_array;
517       const CeedScalar *chebyshev_coeffs, *x_array_read;
518 
519       // -- Interpolate to Chebyshev coefficients
520       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_NOTRANSPOSE, CEED_EVAL_INTERP, u, basis->vec_chebyshev));
521 
522       // -- Evaluate Chebyshev polynomials at arbitrary points
523       CeedCall(CeedVectorGetArrayRead(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
524       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
525       CeedCall(CeedVectorGetArrayWrite(v, CEED_MEM_HOST, &v_array));
526       switch (eval_mode) {
527         case CEED_EVAL_INTERP: {
528           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
529 
530           // ---- Values at point
531           for (CeedInt p = 0; p < total_num_points; p++) {
532             CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
533 
534             for (CeedInt d = 0; d < dim; d++) {
535               // ------ Tensor contract with current Chebyshev polynomial values
536               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
537               CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
538                                                d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
539               pre /= Q_1d;
540               post *= 1;
541             }
542             for (CeedInt c = 0; c < num_comp; c++) v_array[c * total_num_points + p] = tmp[dim % 2][c];
543           }
544           break;
545         }
546         case CEED_EVAL_GRAD: {
547           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
548 
549           // ---- Values at point
550           for (CeedInt p = 0; p < total_num_points; p++) {
551             // Dim**2 contractions, apply grad when pass == dim
552             for (CeedInt pass = 0; pass < dim; pass++) {
553               CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
554 
555               for (CeedInt d = 0; d < dim; d++) {
556                 // ------ Tensor contract with current Chebyshev polynomial values
557                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
558                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
559                 CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
560                                                  d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
561                 pre /= Q_1d;
562                 post *= 1;
563               }
564               for (CeedInt c = 0; c < num_comp; c++) v_array[(pass * num_comp + c) * total_num_points + p] = tmp[dim % 2][c];
565             }
566           }
567           break;
568         }
569         default:
570           // Nothing to do, excluded above
571           break;
572       }
573       CeedCall(CeedVectorRestoreArrayRead(basis->vec_chebyshev, &chebyshev_coeffs));
574       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
575       CeedCall(CeedVectorRestoreArray(v, &v_array));
576       break;
577     }
578     case CEED_TRANSPOSE: {
579       // Note: No switch on e_mode here because only CEED_EVAL_INTERP is supported at this time
580       // Arbitrary points to nodes
581       CeedScalar       *chebyshev_coeffs;
582       const CeedScalar *u_array, *x_array_read;
583 
584       // -- Transpose of evaluation of Chebyshev polynomials at arbitrary points
585       CeedCall(CeedVectorGetArrayWrite(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
586       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
587       CeedCall(CeedVectorGetArrayRead(u, CEED_MEM_HOST, &u_array));
588 
589       switch (eval_mode) {
590         case CEED_EVAL_INTERP: {
591           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
592 
593           // ---- Values at point
594           for (CeedInt p = 0; p < total_num_points; p++) {
595             CeedInt pre = num_comp * 1, post = 1;
596 
597             for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[c * total_num_points + p];
598             for (CeedInt d = 0; d < dim; d++) {
599               // ------ Tensor contract with current Chebyshev polynomial values
600               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
601               CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode, p > 0 && d == (dim - 1), tmp[d % 2],
602                                                d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
603               pre /= 1;
604               post *= Q_1d;
605             }
606           }
607           break;
608         }
609         case CEED_EVAL_GRAD: {
610           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
611 
612           // ---- Values at point
613           for (CeedInt p = 0; p < total_num_points; p++) {
614             // Dim**2 contractions, apply grad when pass == dim
615             for (CeedInt pass = 0; pass < dim; pass++) {
616               CeedInt pre = num_comp * 1, post = 1;
617 
618               for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[(pass * num_comp + c) * total_num_points + p];
619               for (CeedInt d = 0; d < dim; d++) {
620                 // ------ Tensor contract with current Chebyshev polynomial values
621                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
622                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
623                 CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode,
624                                                  (p > 0 || (p == 0 && pass > 0)) && d == (dim - 1), tmp[d % 2],
625                                                  d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
626                 pre /= 1;
627                 post *= Q_1d;
628               }
629             }
630           }
631           break;
632         }
633         default:
634           // Nothing to do, excluded above
635           break;
636       }
637       CeedCall(CeedVectorRestoreArray(basis->vec_chebyshev, &chebyshev_coeffs));
638       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
639       CeedCall(CeedVectorRestoreArrayRead(u, &u_array));
640 
641       // -- Interpolate transpose from Chebyshev coefficients
642       if (apply_add) CeedCall(CeedBasisApplyAdd(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
643       else CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
644       break;
645     }
646   }
647   return CEED_ERROR_SUCCESS;
648 }
649 
650 /// @}
651 
652 /// ----------------------------------------------------------------------------
653 /// Ceed Backend API
654 /// ----------------------------------------------------------------------------
655 /// @addtogroup CeedBasisBackend
656 /// @{
657 
658 /**
659   @brief Fallback to a reference implementation for a non tensor-product basis for \f$H^1\f$ discretizations.
660     This function may only be called inside of a backend `BasisCreateH1` function.
661     This is used by a backend when the specific parameters for a `CeedBasis` exceed the backend's support, such as
662     when a `interp` and `grad` matrices require too many bytes to fit into shared memory on a GPU.
663 
664   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
665   @param[in]  topo      Topology of element, e.g. hypercube, simplex, etc
666   @param[in]  num_comp  Number of field components (1 for scalar fields)
667   @param[in]  num_nodes Total number of nodes
668   @param[in]  num_qpts  Total number of quadrature points
669   @param[in]  interp    Row-major (`num_qpts * num_nodes`) matrix expressing the values of nodal basis functions at quadrature points
670   @param[in]  grad      Row-major (`dim * num_qpts * num_nodes`) matrix expressing derivatives of nodal basis functions at quadrature points
671   @param[in]  q_ref     Array of length `num_qpts * dim` holding the locations of quadrature points on the reference element
672   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
673   @param[out] basis     Newly created `CeedBasis`
674 
675   @return An error code: 0 - success, otherwise - failure
676 
677   @ref User
678 **/
679 int CeedBasisCreateH1Fallback(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
680                               const CeedScalar *grad, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis basis) {
681   CeedInt P = num_nodes, Q = num_qpts, dim = 0;
682   Ceed    delegate;
683 
684   CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
685   CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateH1");
686 
687   CeedCall(CeedReferenceCopy(delegate, &(basis)->ceed));
688   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
689   CeedCall(delegate->BasisCreateH1(topo, dim, P, Q, interp, grad, q_ref, q_weight, basis));
690   CeedCall(CeedDestroy(&delegate));
691   return CEED_ERROR_SUCCESS;
692 }
693 
694 /**
695   @brief Return collocated gradient matrix
696 
697   @param[in]  basis         `CeedBasis`
698   @param[out] collo_grad_1d Row-major (`Q_1d * Q_1d`) matrix expressing derivatives of basis functions at quadrature points
699 
700   @return An error code: 0 - success, otherwise - failure
701 
702   @ref Backend
703 **/
704 int CeedBasisGetCollocatedGrad(CeedBasis basis, CeedScalar *collo_grad_1d) {
705   Ceed              ceed;
706   CeedInt           P_1d, Q_1d;
707   CeedScalar       *interp_1d_pinv;
708   const CeedScalar *grad_1d, *interp_1d;
709 
710   // Note: This function is for backend use, so all errors are terminal and we do not need to clean up memory on failure.
711   CeedCall(CeedBasisGetCeed(basis, &ceed));
712   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
713   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
714 
715   // Compute interp_1d^+, pseudoinverse of interp_1d
716   CeedCall(CeedCalloc(P_1d * Q_1d, &interp_1d_pinv));
717   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
718   CeedCall(CeedMatrixPseudoinverse(ceed, interp_1d, Q_1d, P_1d, interp_1d_pinv));
719   CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
720   CeedCall(CeedMatrixMatrixMultiply(ceed, grad_1d, (const CeedScalar *)interp_1d_pinv, collo_grad_1d, Q_1d, Q_1d, P_1d));
721 
722   CeedCall(CeedFree(&interp_1d_pinv));
723   CeedCall(CeedDestroy(&ceed));
724   return CEED_ERROR_SUCCESS;
725 }
726 
727 /**
728   @brief Return 1D interpolation matrix to Chebyshev polynomial coefficients on quadrature space
729 
730   @param[in]  basis               `CeedBasis`
731   @param[out] chebyshev_interp_1d Row-major (`P_1d * Q_1d`) matrix interpolating from basis nodes to Chebyshev polynomial coefficients
732 
733   @return An error code: 0 - success, otherwise - failure
734 
735   @ref Backend
736 **/
737 int CeedBasisGetChebyshevInterp1D(CeedBasis basis, CeedScalar *chebyshev_interp_1d) {
738   CeedInt           P_1d, Q_1d;
739   CeedScalar       *C, *chebyshev_coeffs_1d_inv;
740   const CeedScalar *interp_1d, *q_ref_1d;
741   Ceed              ceed;
742 
743   CeedCall(CeedBasisGetCeed(basis, &ceed));
744   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
745   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
746 
747   // Build coefficient matrix
748   // -- Note: Clang-tidy needs this check
749   CeedCheck((P_1d > 0) && (Q_1d > 0), ceed, CEED_ERROR_INCOMPATIBLE, "CeedBasis dimensions are malformed");
750   CeedCall(CeedCalloc(Q_1d * Q_1d, &C));
751   CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
752   for (CeedInt i = 0; i < Q_1d; i++) CeedCall(CeedChebyshevPolynomialsAtPoint(q_ref_1d[i], Q_1d, &C[i * Q_1d]));
753 
754   // Compute C^+, pseudoinverse of coefficient matrix
755   CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_coeffs_1d_inv));
756   CeedCall(CeedMatrixPseudoinverse(ceed, C, Q_1d, Q_1d, chebyshev_coeffs_1d_inv));
757 
758   // Build mapping from nodes to Chebyshev coefficients
759   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
760   CeedCall(CeedMatrixMatrixMultiply(ceed, chebyshev_coeffs_1d_inv, interp_1d, chebyshev_interp_1d, Q_1d, P_1d, Q_1d));
761 
762   // Cleanup
763   CeedCall(CeedFree(&C));
764   CeedCall(CeedFree(&chebyshev_coeffs_1d_inv));
765   CeedCall(CeedDestroy(&ceed));
766   return CEED_ERROR_SUCCESS;
767 }
768 
769 /**
770   @brief Get tensor status for given `CeedBasis`
771 
772   @param[in]  basis     `CeedBasis`
773   @param[out] is_tensor Variable to store tensor status
774 
775   @return An error code: 0 - success, otherwise - failure
776 
777   @ref Backend
778 **/
779 int CeedBasisIsTensor(CeedBasis basis, bool *is_tensor) {
780   *is_tensor = basis->is_tensor_basis;
781   return CEED_ERROR_SUCCESS;
782 }
783 
784 /**
785   @brief Determine if given `CeedBasis` has nodes collocated with quadrature points
786 
787   @param[in]  basis         `CeedBasis`
788   @param[out] is_collocated Variable to store collocated status
789 
790   @return An error code: 0 - success, otherwise - failure
791 
792   @ref Backend
793 **/
794 int CeedBasisIsCollocated(CeedBasis basis, bool *is_collocated) {
795   if (basis->is_tensor_basis && (basis->Q_1d == basis->P_1d)) {
796     *is_collocated = true;
797 
798     for (CeedInt i = 0; i < basis->P_1d; i++) {
799       *is_collocated = *is_collocated && (fabs(basis->interp_1d[i + basis->P_1d * i] - 1.0) < 10 * CEED_EPSILON);
800       for (CeedInt j = 0; j < basis->Q_1d; j++) {
801         if (j != i) *is_collocated = *is_collocated && (fabs(basis->interp_1d[j + basis->P_1d * i]) < 10 * CEED_EPSILON);
802       }
803     }
804   } else {
805     *is_collocated = false;
806   }
807   return CEED_ERROR_SUCCESS;
808 }
809 
810 /**
811   @brief Get backend data of a `CeedBasis`
812 
813   @param[in]  basis `CeedBasis`
814   @param[out] data  Variable to store data
815 
816   @return An error code: 0 - success, otherwise - failure
817 
818   @ref Backend
819 **/
820 int CeedBasisGetData(CeedBasis basis, void *data) {
821   *(void **)data = basis->data;
822   return CEED_ERROR_SUCCESS;
823 }
824 
825 /**
826   @brief Set backend data of a `CeedBasis`
827 
828   @param[in,out] basis  `CeedBasis`
829   @param[in]     data   Data to set
830 
831   @return An error code: 0 - success, otherwise - failure
832 
833   @ref Backend
834 **/
835 int CeedBasisSetData(CeedBasis basis, void *data) {
836   basis->data = data;
837   return CEED_ERROR_SUCCESS;
838 }
839 
840 /**
841   @brief Increment the reference counter for a `CeedBasis`
842 
843   @param[in,out] basis `CeedBasis` to increment the reference counter
844 
845   @return An error code: 0 - success, otherwise - failure
846 
847   @ref Backend
848 **/
849 int CeedBasisReference(CeedBasis basis) {
850   basis->ref_count++;
851   return CEED_ERROR_SUCCESS;
852 }
853 
854 /**
855   @brief Get number of Q-vector components for given `CeedBasis`
856 
857   @param[in]  basis     `CeedBasis`
858   @param[in]  eval_mode @ref CEED_EVAL_INTERP to use interpolated values,
859                           @ref CEED_EVAL_GRAD to use gradients,
860                           @ref CEED_EVAL_DIV to use divergence,
861                           @ref CEED_EVAL_CURL to use curl
862   @param[out] q_comp    Variable to store number of Q-vector components of basis
863 
864   @return An error code: 0 - success, otherwise - failure
865 
866   @ref Backend
867 **/
868 int CeedBasisGetNumQuadratureComponents(CeedBasis basis, CeedEvalMode eval_mode, CeedInt *q_comp) {
869   CeedInt dim;
870 
871   CeedCall(CeedBasisGetDimension(basis, &dim));
872   switch (eval_mode) {
873     case CEED_EVAL_INTERP: {
874       CeedFESpace fe_space;
875 
876       CeedCall(CeedBasisGetFESpace(basis, &fe_space));
877       *q_comp = (fe_space == CEED_FE_SPACE_H1) ? 1 : dim;
878     } break;
879     case CEED_EVAL_GRAD:
880       *q_comp = dim;
881       break;
882     case CEED_EVAL_DIV:
883       *q_comp = 1;
884       break;
885     case CEED_EVAL_CURL:
886       *q_comp = (dim < 3) ? 1 : dim;
887       break;
888     case CEED_EVAL_NONE:
889     case CEED_EVAL_WEIGHT:
890       *q_comp = 1;
891       break;
892   }
893   return CEED_ERROR_SUCCESS;
894 }
895 
896 /**
897   @brief Estimate number of FLOPs required to apply `CeedBasis` in `t_mode` and `eval_mode`
898 
899   @param[in]  basis        `CeedBasis` to estimate FLOPs for
900   @param[in]  t_mode       Apply basis or transpose
901   @param[in]  eval_mode    @ref CeedEvalMode
902   @param[in]  is_at_points Evaluate the basis at points or quadrature points
903   @param[in]  num_points   Number of points basis is evaluated at
904   @param[out] flops        Address of variable to hold FLOPs estimate
905 
906   @ref Backend
907 **/
908 int CeedBasisGetFlopsEstimate(CeedBasis basis, CeedTransposeMode t_mode, CeedEvalMode eval_mode, bool is_at_points, CeedInt num_points,
909                               CeedSize *flops) {
910   bool is_tensor;
911 
912   CeedCall(CeedBasisIsTensor(basis, &is_tensor));
913   CeedCheck(!is_at_points || is_tensor, CeedBasisReturnCeed(basis), CEED_ERROR_INCOMPATIBLE, "Can only evaluate tensor-product bases at points");
914   if (is_tensor) {
915     CeedInt dim, num_comp, P_1d, Q_1d;
916 
917     CeedCall(CeedBasisGetDimension(basis, &dim));
918     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
919     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
920     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
921     if (t_mode == CEED_TRANSPOSE) {
922       P_1d = Q_1d;
923       Q_1d = P_1d;
924     }
925     CeedInt tensor_flops = 0, pre = num_comp * CeedIntPow(P_1d, dim - 1), post = 1;
926 
927     for (CeedInt d = 0; d < dim; d++) {
928       tensor_flops += 2 * pre * P_1d * post * Q_1d;
929       pre /= P_1d;
930       post *= Q_1d;
931     }
932     if (is_at_points) {
933       bool is_gpu = false;
934 
935       {
936         CeedMemType mem_type;
937 
938         CeedCall(CeedGetPreferredMemType(CeedBasisReturnCeed(basis), &mem_type));
939         is_gpu = mem_type == CEED_MEM_DEVICE;
940       }
941 
942       CeedInt chebyshev_flops = (Q_1d - 2) * 3 + 1, d_chebyshev_flops = (Q_1d - 2) * 8 + 1;
943       CeedInt point_tensor_flops = 0, pre = CeedIntPow(Q_1d, dim - 1), post = 1;
944 
945       for (CeedInt d = 0; d < dim; d++) {
946         point_tensor_flops += 2 * pre * Q_1d * post * 1;
947         pre /= P_1d;
948         post *= Q_1d;
949       }
950 
951       switch (eval_mode) {
952         case CEED_EVAL_NONE:
953           *flops = 0;
954           break;
955         case CEED_EVAL_INTERP: {
956           *flops = tensor_flops + num_points * num_comp * (point_tensor_flops + (t_mode == CEED_TRANSPOSE ? CeedIntPow(Q_1d, dim) : 0));
957           if (dim == 3 && is_gpu) {
958             *flops += num_points * Q_1d *
959                       (chebyshev_flops + num_comp * (2 * chebyshev_flops + 2 * Q_1d * Q_1d + (t_mode == CEED_TRANSPOSE ? 2 * Q_1d + 1 : 3 * Q_1d)));
960           } else {
961             *flops += num_points * (is_gpu ? num_comp : 1) * dim * chebyshev_flops;
962           }
963           break;
964         }
965         case CEED_EVAL_GRAD: {
966           *flops = tensor_flops + num_points * num_comp * (point_tensor_flops + (t_mode == CEED_TRANSPOSE ? CeedIntPow(Q_1d, dim) : 0));
967           if (dim == 3 && is_gpu) {
968             CeedInt inner_flops =
969                 dim * (2 * Q_1d * Q_1d + (t_mode == CEED_TRANSPOSE ? 2 : 3) * Q_1d) + (dim - 1) * (2 * chebyshev_flops + d_chebyshev_flops);
970 
971             *flops += num_points * Q_1d * (chebyshev_flops + d_chebyshev_flops + num_comp * (inner_flops + (t_mode == CEED_TRANSPOSE ? 1 : 0)));
972           } else {
973             *flops += num_points * (is_gpu ? num_comp : 1) * dim * (d_chebyshev_flops + (dim - 1) * chebyshev_flops);
974           }
975           break;
976         }
977         case CEED_EVAL_DIV:
978         case CEED_EVAL_CURL: {
979           // LCOV_EXCL_START
980           return CeedError(CeedBasisReturnCeed(basis), CEED_ERROR_INCOMPATIBLE, "Tensor basis evaluation for %s not supported at points",
981                            CeedEvalModes[eval_mode]);
982           break;
983           // LCOV_EXCL_STOP
984         }
985         case CEED_EVAL_WEIGHT:
986           *flops = num_points;
987           break;
988       }
989     } else {
990       switch (eval_mode) {
991         case CEED_EVAL_NONE:
992           *flops = 0;
993           break;
994         case CEED_EVAL_INTERP:
995           *flops = tensor_flops;
996           break;
997         case CEED_EVAL_GRAD:
998           *flops = tensor_flops * 2;
999           break;
1000         case CEED_EVAL_DIV:
1001         case CEED_EVAL_CURL: {
1002           // LCOV_EXCL_START
1003           return CeedError(CeedBasisReturnCeed(basis), CEED_ERROR_INCOMPATIBLE, "Tensor basis evaluation for %s not supported",
1004                            CeedEvalModes[eval_mode]);
1005           break;
1006           // LCOV_EXCL_STOP
1007         }
1008         case CEED_EVAL_WEIGHT:
1009           *flops = dim * CeedIntPow(Q_1d, dim);
1010           break;
1011       }
1012     }
1013   } else {
1014     CeedInt dim, num_comp, q_comp, num_nodes, num_qpts;
1015 
1016     CeedCall(CeedBasisGetDimension(basis, &dim));
1017     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1018     CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
1019     CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1020     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
1021     switch (eval_mode) {
1022       case CEED_EVAL_NONE:
1023         *flops = 0;
1024         break;
1025       case CEED_EVAL_INTERP:
1026       case CEED_EVAL_GRAD:
1027       case CEED_EVAL_DIV:
1028       case CEED_EVAL_CURL:
1029         *flops = num_nodes * num_qpts * num_comp * q_comp;
1030         break;
1031       case CEED_EVAL_WEIGHT:
1032         *flops = 0;
1033         break;
1034     }
1035   }
1036   return CEED_ERROR_SUCCESS;
1037 }
1038 
1039 /**
1040   @brief Get `CeedFESpace` for a `CeedBasis`
1041 
1042   @param[in]  basis    `CeedBasis`
1043   @param[out] fe_space Variable to store `CeedFESpace`
1044 
1045   @return An error code: 0 - success, otherwise - failure
1046 
1047   @ref Backend
1048 **/
1049 int CeedBasisGetFESpace(CeedBasis basis, CeedFESpace *fe_space) {
1050   *fe_space = basis->fe_space;
1051   return CEED_ERROR_SUCCESS;
1052 }
1053 
1054 /**
1055   @brief Get dimension for given `CeedElemTopology`
1056 
1057   @param[in]  topo `CeedElemTopology`
1058   @param[out] dim  Variable to store dimension of topology
1059 
1060   @return An error code: 0 - success, otherwise - failure
1061 
1062   @ref Backend
1063 **/
1064 int CeedBasisGetTopologyDimension(CeedElemTopology topo, CeedInt *dim) {
1065   *dim = (CeedInt)topo >> 16;
1066   return CEED_ERROR_SUCCESS;
1067 }
1068 
1069 /**
1070   @brief Get `CeedTensorContract` of a `CeedBasis`
1071 
1072   @param[in]  basis     `CeedBasis`
1073   @param[out] contract  Variable to store `CeedTensorContract`
1074 
1075   @return An error code: 0 - success, otherwise - failure
1076 
1077   @ref Backend
1078 **/
1079 int CeedBasisGetTensorContract(CeedBasis basis, CeedTensorContract *contract) {
1080   *contract = basis->contract;
1081   return CEED_ERROR_SUCCESS;
1082 }
1083 
1084 /**
1085   @brief Set `CeedTensorContract` of a `CeedBasis`
1086 
1087   @param[in,out] basis    `CeedBasis`
1088   @param[in]     contract `CeedTensorContract` to set
1089 
1090   @return An error code: 0 - success, otherwise - failure
1091 
1092   @ref Backend
1093 **/
1094 int CeedBasisSetTensorContract(CeedBasis basis, CeedTensorContract contract) {
1095   basis->contract = contract;
1096   CeedCall(CeedTensorContractReference(contract));
1097   return CEED_ERROR_SUCCESS;
1098 }
1099 
1100 /**
1101   @brief Return a reference implementation of matrix multiplication \f$C = A B\f$.
1102 
1103   Note: This is a reference implementation for CPU `CeedScalar` pointers that is not intended for high performance.
1104 
1105   @param[in]  ceed  `Ceed` context for error handling
1106   @param[in]  mat_A Row-major matrix `A`
1107   @param[in]  mat_B Row-major matrix `B`
1108   @param[out] mat_C Row-major output matrix `C`
1109   @param[in]  m     Number of rows of `C`
1110   @param[in]  n     Number of columns of `C`
1111   @param[in]  kk    Number of columns of `A`/rows of `B`
1112 
1113   @return An error code: 0 - success, otherwise - failure
1114 
1115   @ref Utility
1116 **/
1117 int CeedMatrixMatrixMultiply(Ceed ceed, const CeedScalar *mat_A, const CeedScalar *mat_B, CeedScalar *mat_C, CeedInt m, CeedInt n, CeedInt kk) {
1118   for (CeedInt i = 0; i < m; i++) {
1119     for (CeedInt j = 0; j < n; j++) {
1120       CeedScalar sum = 0;
1121 
1122       for (CeedInt k = 0; k < kk; k++) sum += mat_A[k + i * kk] * mat_B[j + k * n];
1123       mat_C[j + i * n] = sum;
1124     }
1125   }
1126   return CEED_ERROR_SUCCESS;
1127 }
1128 
1129 /**
1130   @brief Return QR Factorization of a matrix
1131 
1132   @param[in]     ceed `Ceed` context for error handling
1133   @param[in,out] mat  Row-major matrix to be factorized in place
1134   @param[in,out] tau  Vector of length `m` of scaling factors
1135   @param[in]     m    Number of rows
1136   @param[in]     n    Number of columns
1137 
1138   @return An error code: 0 - success, otherwise - failure
1139 
1140   @ref Utility
1141 **/
1142 int CeedQRFactorization(Ceed ceed, CeedScalar *mat, CeedScalar *tau, CeedInt m, CeedInt n) {
1143   CeedScalar v[m];
1144 
1145   // Check matrix shape
1146   CeedCheck(n <= m, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute QR factorization with n > m");
1147 
1148   for (CeedInt i = 0; i < n; i++) {
1149     CeedScalar sigma = 0.0;
1150 
1151     if (i >= m - 1) {  // last row of matrix, no reflection needed
1152       tau[i] = 0.;
1153       break;
1154     }
1155     // Calculate Householder vector, magnitude
1156     v[i] = mat[i + n * i];
1157     for (CeedInt j = i + 1; j < m; j++) {
1158       v[j] = mat[i + n * j];
1159       sigma += v[j] * v[j];
1160     }
1161     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:m]
1162     const CeedScalar R_ii = -copysign(norm, v[i]);
1163 
1164     v[i] -= R_ii;
1165     // norm of v[i:m] after modification above and scaling below
1166     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
1167     //   tau = 2 / (norm*norm)
1168     tau[i] = 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
1169     for (CeedInt j = i + 1; j < m; j++) v[j] /= v[i];
1170 
1171     // Apply Householder reflector to lower right panel
1172     CeedHouseholderReflect(&mat[i * n + i + 1], &v[i], tau[i], m - i, n - i - 1, n, 1);
1173     // Save v
1174     mat[i + n * i] = R_ii;
1175     for (CeedInt j = i + 1; j < m; j++) mat[i + n * j] = v[j];
1176   }
1177   return CEED_ERROR_SUCCESS;
1178 }
1179 
1180 /**
1181   @brief Apply Householder Q matrix
1182 
1183   Compute `mat_A = mat_Q mat_A`, where `mat_Q` is \f$m \times m\f$ and `mat_A` is \f$m \times n\f$.
1184 
1185   @param[in,out] mat_A  Matrix to apply Householder Q to, in place
1186   @param[in]     mat_Q  Householder Q matrix
1187   @param[in]     tau    Householder scaling factors
1188   @param[in]     t_mode Transpose mode for application
1189   @param[in]     m      Number of rows in `A`
1190   @param[in]     n      Number of columns in `A`
1191   @param[in]     k      Number of elementary reflectors in Q, `k < m`
1192   @param[in]     row    Row stride in `A`
1193   @param[in]     col    Col stride in `A`
1194 
1195   @return An error code: 0 - success, otherwise - failure
1196 
1197   @ref Utility
1198 **/
1199 int CeedHouseholderApplyQ(CeedScalar *mat_A, const CeedScalar *mat_Q, const CeedScalar *tau, CeedTransposeMode t_mode, CeedInt m, CeedInt n,
1200                           CeedInt k, CeedInt row, CeedInt col) {
1201   CeedScalar *v;
1202 
1203   CeedCall(CeedMalloc(m, &v));
1204   for (CeedInt ii = 0; ii < k; ii++) {
1205     CeedInt i = t_mode == CEED_TRANSPOSE ? ii : k - 1 - ii;
1206     for (CeedInt j = i + 1; j < m; j++) v[j] = mat_Q[j * k + i];
1207     // Apply Householder reflector (I - tau v v^T) collo_grad_1d^T
1208     CeedCall(CeedHouseholderReflect(&mat_A[i * row], &v[i], tau[i], m - i, n, row, col));
1209   }
1210   CeedCall(CeedFree(&v));
1211   return CEED_ERROR_SUCCESS;
1212 }
1213 
1214 /**
1215   @brief Return pseudoinverse of a matrix
1216 
1217   @param[in]     ceed      Ceed context for error handling
1218   @param[in]     mat       Row-major matrix to compute pseudoinverse of
1219   @param[in]     m         Number of rows
1220   @param[in]     n         Number of columns
1221   @param[out]    mat_pinv  Row-major pseudoinverse matrix
1222 
1223   @return An error code: 0 - success, otherwise - failure
1224 
1225   @ref Utility
1226 **/
1227 int CeedMatrixPseudoinverse(Ceed ceed, const CeedScalar *mat, CeedInt m, CeedInt n, CeedScalar *mat_pinv) {
1228   CeedScalar *tau, *I, *mat_copy;
1229 
1230   CeedCall(CeedCalloc(m, &tau));
1231   CeedCall(CeedCalloc(m * m, &I));
1232   CeedCall(CeedCalloc(m * n, &mat_copy));
1233   memcpy(mat_copy, mat, m * n * sizeof mat[0]);
1234 
1235   // QR Factorization, mat = Q R
1236   CeedCall(CeedQRFactorization(ceed, mat_copy, tau, m, n));
1237 
1238   // -- Apply Q^T, I = Q^T * I
1239   for (CeedInt i = 0; i < m; i++) I[i * m + i] = 1.0;
1240   CeedCall(CeedHouseholderApplyQ(I, mat_copy, tau, CEED_TRANSPOSE, m, m, n, m, 1));
1241   // -- Apply R_inv, mat_pinv = R_inv * Q^T
1242   for (CeedInt j = 0; j < m; j++) {  // Column j
1243     mat_pinv[j + m * (n - 1)] = I[j + m * (n - 1)] / mat_copy[n * n - 1];
1244     for (CeedInt i = n - 2; i >= 0; i--) {  // Row i
1245       mat_pinv[j + m * i] = I[j + m * i];
1246       for (CeedInt k = i + 1; k < n; k++) mat_pinv[j + m * i] -= mat_copy[k + n * i] * mat_pinv[j + m * k];
1247       mat_pinv[j + m * i] /= mat_copy[i + n * i];
1248     }
1249   }
1250 
1251   // Cleanup
1252   CeedCall(CeedFree(&I));
1253   CeedCall(CeedFree(&tau));
1254   CeedCall(CeedFree(&mat_copy));
1255   return CEED_ERROR_SUCCESS;
1256 }
1257 
1258 /**
1259   @brief Return symmetric Schur decomposition of the symmetric matrix mat via symmetric QR factorization
1260 
1261   @param[in]     ceed   `Ceed` context for error handling
1262   @param[in,out] mat    Row-major matrix to be factorized in place
1263   @param[out]    lambda Vector of length n of eigenvalues
1264   @param[in]     n      Number of rows/columns
1265 
1266   @return An error code: 0 - success, otherwise - failure
1267 
1268   @ref Utility
1269 **/
1270 CeedPragmaOptimizeOff
1271 int CeedSymmetricSchurDecomposition(Ceed ceed, CeedScalar *mat, CeedScalar *lambda, CeedInt n) {
1272   // Check bounds for clang-tidy
1273   CeedCheck(n > 1, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute symmetric Schur decomposition of scalars");
1274 
1275   CeedScalar v[n - 1], tau[n - 1], mat_T[n * n];
1276 
1277   // Copy mat to mat_T and set mat to I
1278   memcpy(mat_T, mat, n * n * sizeof(mat[0]));
1279   for (CeedInt i = 0; i < n; i++) {
1280     for (CeedInt j = 0; j < n; j++) mat[j + n * i] = (i == j) ? 1 : 0;
1281   }
1282 
1283   // Reduce to tridiagonal
1284   for (CeedInt i = 0; i < n - 1; i++) {
1285     // Calculate Householder vector, magnitude
1286     CeedScalar sigma = 0.0;
1287 
1288     v[i] = mat_T[i + n * (i + 1)];
1289     for (CeedInt j = i + 1; j < n - 1; j++) {
1290       v[j] = mat_T[i + n * (j + 1)];
1291       sigma += v[j] * v[j];
1292     }
1293     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:n-1]
1294     const CeedScalar R_ii = -copysign(norm, v[i]);
1295 
1296     v[i] -= R_ii;
1297     // norm of v[i:m] after modification above and scaling below
1298     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
1299     //   tau = 2 / (norm*norm)
1300     tau[i] = i == n - 2 ? 2 : 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
1301     for (CeedInt j = i + 1; j < n - 1; j++) v[j] /= v[i];
1302 
1303     // Update sub and super diagonal
1304     for (CeedInt j = i + 2; j < n; j++) {
1305       mat_T[i + n * j] = 0;
1306       mat_T[j + n * i] = 0;
1307     }
1308     // Apply symmetric Householder reflector to lower right panel
1309     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1310     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), 1, n);
1311 
1312     // Save v
1313     mat_T[i + n * (i + 1)] = R_ii;
1314     mat_T[(i + 1) + n * i] = R_ii;
1315     for (CeedInt j = i + 1; j < n - 1; j++) {
1316       mat_T[i + n * (j + 1)] = v[j];
1317     }
1318   }
1319   // Backwards accumulation of Q
1320   for (CeedInt i = n - 2; i >= 0; i--) {
1321     if (tau[i] > 0.0) {
1322       v[i] = 1;
1323       for (CeedInt j = i + 1; j < n - 1; j++) {
1324         v[j]                   = mat_T[i + n * (j + 1)];
1325         mat_T[i + n * (j + 1)] = 0;
1326       }
1327       CeedHouseholderReflect(&mat[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1328     }
1329   }
1330 
1331   // Reduce sub and super diagonal
1332   CeedInt    p = 0, q = 0, itr = 0, max_itr = n * n * n * n;
1333   CeedScalar tol = CEED_EPSILON;
1334 
1335   while (itr < max_itr) {
1336     // Update p, q, size of reduced portions of diagonal
1337     p = 0;
1338     q = 0;
1339     for (CeedInt i = n - 2; i >= 0; i--) {
1340       if (fabs(mat_T[i + n * (i + 1)]) < tol) q += 1;
1341       else break;
1342     }
1343     for (CeedInt i = 0; i < n - q - 1; i++) {
1344       if (fabs(mat_T[i + n * (i + 1)]) < tol) p += 1;
1345       else break;
1346     }
1347     if (q == n - 1) break;  // Finished reducing
1348 
1349     // Reduce tridiagonal portion
1350     CeedScalar t_nn = mat_T[(n - 1 - q) + n * (n - 1 - q)], t_nnm1 = mat_T[(n - 2 - q) + n * (n - 1 - q)];
1351     CeedScalar d  = (mat_T[(n - 2 - q) + n * (n - 2 - q)] - t_nn) / 2;
1352     CeedScalar mu = t_nn - t_nnm1 * t_nnm1 / (d + copysign(sqrt(d * d + t_nnm1 * t_nnm1), d));
1353     CeedScalar x  = mat_T[p + n * p] - mu;
1354     CeedScalar z  = mat_T[p + n * (p + 1)];
1355 
1356     for (CeedInt k = p; k < n - q - 1; k++) {
1357       // Compute Givens rotation
1358       CeedScalar c = 1, s = 0;
1359 
1360       if (fabs(z) > tol) {
1361         if (fabs(z) > fabs(x)) {
1362           const CeedScalar tau = -x / z;
1363 
1364           s = 1 / sqrt(1 + tau * tau);
1365           c = s * tau;
1366         } else {
1367           const CeedScalar tau = -z / x;
1368 
1369           c = 1 / sqrt(1 + tau * tau);
1370           s = c * tau;
1371         }
1372       }
1373 
1374       // Apply Givens rotation to T
1375       CeedGivensRotation(mat_T, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1376       CeedGivensRotation(mat_T, c, s, CEED_TRANSPOSE, k, k + 1, n, n);
1377 
1378       // Apply Givens rotation to Q
1379       CeedGivensRotation(mat, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1380 
1381       // Update x, z
1382       if (k < n - q - 2) {
1383         x = mat_T[k + n * (k + 1)];
1384         z = mat_T[k + n * (k + 2)];
1385       }
1386     }
1387     itr++;
1388   }
1389 
1390   // Save eigenvalues
1391   for (CeedInt i = 0; i < n; i++) lambda[i] = mat_T[i + n * i];
1392 
1393   // Check convergence
1394   CeedCheck(itr < max_itr || q > n, ceed, CEED_ERROR_MINOR, "Symmetric QR failed to converge");
1395   return CEED_ERROR_SUCCESS;
1396 }
1397 CeedPragmaOptimizeOn
1398 
1399 /**
1400   @brief Return Simultaneous Diagonalization of two matrices.
1401 
1402   This solves the generalized eigenvalue problem `A x = lambda B x`, where `A` and `B` are symmetric and `B` is positive definite.
1403   We generate the matrix `X` and vector `Lambda` such that `X^T A X = Lambda` and `X^T B X = I`.
1404   This is equivalent to the LAPACK routine 'sygv' with `TYPE = 1`.
1405 
1406   @param[in]  ceed   `Ceed` context for error handling
1407   @param[in]  mat_A  Row-major matrix to be factorized with eigenvalues
1408   @param[in]  mat_B  Row-major matrix to be factorized to identity
1409   @param[out] mat_X  Row-major orthogonal matrix
1410   @param[out] lambda Vector of length `n` of generalized eigenvalues
1411   @param[in]  n      Number of rows/columns
1412 
1413   @return An error code: 0 - success, otherwise - failure
1414 
1415   @ref Utility
1416 **/
1417 CeedPragmaOptimizeOff
1418 int CeedSimultaneousDiagonalization(Ceed ceed, CeedScalar *mat_A, CeedScalar *mat_B, CeedScalar *mat_X, CeedScalar *lambda, CeedInt n) {
1419   CeedScalar *mat_C, *mat_G, *vec_D;
1420 
1421   CeedCall(CeedCalloc(n * n, &mat_C));
1422   CeedCall(CeedCalloc(n * n, &mat_G));
1423   CeedCall(CeedCalloc(n, &vec_D));
1424 
1425   // Compute B = G D G^T
1426   memcpy(mat_G, mat_B, n * n * sizeof(mat_B[0]));
1427   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_G, vec_D, n));
1428 
1429   // Sort eigenvalues
1430   for (CeedInt i = n - 1; i >= 0; i--) {
1431     for (CeedInt j = 0; j < i; j++) {
1432       if (fabs(vec_D[j]) > fabs(vec_D[j + 1])) {
1433         CeedScalarSwap(vec_D[j], vec_D[j + 1]);
1434         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_G[k * n + j], mat_G[k * n + j + 1]);
1435       }
1436     }
1437   }
1438 
1439   // Compute C = (G D^1/2)^-1 A (G D^1/2)^-T
1440   //           = D^-1/2 G^T A G D^-1/2
1441   // -- D = D^-1/2
1442   for (CeedInt i = 0; i < n; i++) vec_D[i] = 1. / sqrt(vec_D[i]);
1443   // -- G = G D^-1/2
1444   // -- C = D^-1/2 G^T
1445   for (CeedInt i = 0; i < n; i++) {
1446     for (CeedInt j = 0; j < n; j++) {
1447       mat_G[i * n + j] *= vec_D[j];
1448       mat_C[j * n + i] = mat_G[i * n + j];
1449     }
1450   }
1451   // -- X = (D^-1/2 G^T) A
1452   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_C, (const CeedScalar *)mat_A, mat_X, n, n, n));
1453   // -- C = (D^-1/2 G^T A) (G D^-1/2)
1454   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_X, (const CeedScalar *)mat_G, mat_C, n, n, n));
1455 
1456   // Compute Q^T C Q = lambda
1457   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_C, lambda, n));
1458 
1459   // Sort eigenvalues
1460   for (CeedInt i = n - 1; i >= 0; i--) {
1461     for (CeedInt j = 0; j < i; j++) {
1462       if (fabs(lambda[j]) > fabs(lambda[j + 1])) {
1463         CeedScalarSwap(lambda[j], lambda[j + 1]);
1464         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_C[k * n + j], mat_C[k * n + j + 1]);
1465       }
1466     }
1467   }
1468 
1469   // Set X = (G D^1/2)^-T Q
1470   //       = G D^-1/2 Q
1471   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_G, (const CeedScalar *)mat_C, mat_X, n, n, n));
1472 
1473   // Cleanup
1474   CeedCall(CeedFree(&mat_C));
1475   CeedCall(CeedFree(&mat_G));
1476   CeedCall(CeedFree(&vec_D));
1477   return CEED_ERROR_SUCCESS;
1478 }
1479 CeedPragmaOptimizeOn
1480 
1481 /// @}
1482 
1483 /// ----------------------------------------------------------------------------
1484 /// CeedBasis Public API
1485 /// ----------------------------------------------------------------------------
1486 /// @addtogroup CeedBasisUser
1487 /// @{
1488 
1489 /**
1490   @brief Create a tensor-product basis for \f$H^1\f$ discretizations
1491 
1492   @param[in]  ceed        `Ceed` object used to create the `CeedBasis`
1493   @param[in]  dim         Topological dimension
1494   @param[in]  num_comp    Number of field components (1 for scalar fields)
1495   @param[in]  P_1d        Number of nodes in one dimension
1496   @param[in]  Q_1d        Number of quadrature points in one dimension
1497   @param[in]  interp_1d   Row-major (`Q_1d * P_1d`) matrix expressing the values of nodal basis functions at quadrature points
1498   @param[in]  grad_1d     Row-major (`Q_1d * P_1d`) matrix expressing derivatives of nodal basis functions at quadrature points
1499   @param[in]  q_ref_1d    Array of length `Q_1d` holding the locations of quadrature points on the 1D reference element `[-1, 1]`
1500   @param[in]  q_weight_1d Array of length `Q_1d` holding the quadrature weights on the reference element
1501   @param[out] basis       Address of the variable where the newly created `CeedBasis` will be stored
1502 
1503   @return An error code: 0 - success, otherwise - failure
1504 
1505   @ref User
1506 **/
1507 int CeedBasisCreateTensorH1(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P_1d, CeedInt Q_1d, const CeedScalar *interp_1d,
1508                             const CeedScalar *grad_1d, const CeedScalar *q_ref_1d, const CeedScalar *q_weight_1d, CeedBasis *basis) {
1509   if (!ceed->BasisCreateTensorH1) {
1510     Ceed delegate;
1511 
1512     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1513     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateTensorH1");
1514     CeedCall(CeedBasisCreateTensorH1(delegate, dim, num_comp, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1515     CeedCall(CeedDestroy(&delegate));
1516     return CEED_ERROR_SUCCESS;
1517   }
1518 
1519   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1520   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1521   CeedCheck(P_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1522   CeedCheck(Q_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1523 
1524   CeedElemTopology topo = dim == 1 ? CEED_TOPOLOGY_LINE : dim == 2 ? CEED_TOPOLOGY_QUAD : CEED_TOPOLOGY_HEX;
1525 
1526   CeedCall(CeedCalloc(1, basis));
1527   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1528   (*basis)->ref_count       = 1;
1529   (*basis)->is_tensor_basis = true;
1530   (*basis)->dim             = dim;
1531   (*basis)->topo            = topo;
1532   (*basis)->num_comp        = num_comp;
1533   (*basis)->P_1d            = P_1d;
1534   (*basis)->Q_1d            = Q_1d;
1535   (*basis)->P               = CeedIntPow(P_1d, dim);
1536   (*basis)->Q               = CeedIntPow(Q_1d, dim);
1537   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1538   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_ref_1d));
1539   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_weight_1d));
1540   if (q_ref_1d) memcpy((*basis)->q_ref_1d, q_ref_1d, Q_1d * sizeof(q_ref_1d[0]));
1541   if (q_weight_1d) memcpy((*basis)->q_weight_1d, q_weight_1d, Q_1d * sizeof(q_weight_1d[0]));
1542   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->interp_1d));
1543   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->grad_1d));
1544   if (interp_1d) memcpy((*basis)->interp_1d, interp_1d, Q_1d * P_1d * sizeof(interp_1d[0]));
1545   if (grad_1d) memcpy((*basis)->grad_1d, grad_1d, Q_1d * P_1d * sizeof(grad_1d[0]));
1546   CeedCall(ceed->BasisCreateTensorH1(dim, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, *basis));
1547   return CEED_ERROR_SUCCESS;
1548 }
1549 
1550 /**
1551   @brief Create a tensor-product \f$H^1\f$ Lagrange basis
1552 
1553   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1554   @param[in]  dim       Topological dimension of element
1555   @param[in]  num_comp  Number of field components (1 for scalar fields)
1556   @param[in]  P         Number of Gauss-Lobatto nodes in one dimension.
1557                           The polynomial degree of the resulting `Q_k` element is `k = P - 1`.
1558   @param[in]  Q         Number of quadrature points in one dimension.
1559   @param[in]  quad_mode Distribution of the `Q` quadrature points (affects order of accuracy for the quadrature)
1560   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1561 
1562   @return An error code: 0 - success, otherwise - failure
1563 
1564   @ref User
1565 **/
1566 int CeedBasisCreateTensorH1Lagrange(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P, CeedInt Q, CeedQuadMode quad_mode, CeedBasis *basis) {
1567   // Allocate
1568   int        ierr = CEED_ERROR_SUCCESS;
1569   CeedScalar c1, c2, c3, c4, dx, *nodes, *interp_1d, *grad_1d, *q_ref_1d, *q_weight_1d;
1570 
1571   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1572   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1573   CeedCheck(P > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1574   CeedCheck(Q > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1575 
1576   // Get Nodes and Weights
1577   CeedCall(CeedCalloc(P * Q, &interp_1d));
1578   CeedCall(CeedCalloc(P * Q, &grad_1d));
1579   CeedCall(CeedCalloc(P, &nodes));
1580   CeedCall(CeedCalloc(Q, &q_ref_1d));
1581   CeedCall(CeedCalloc(Q, &q_weight_1d));
1582   if (CeedLobattoQuadrature(P, nodes, NULL) != CEED_ERROR_SUCCESS) goto cleanup;
1583   switch (quad_mode) {
1584     case CEED_GAUSS:
1585       ierr = CeedGaussQuadrature(Q, q_ref_1d, q_weight_1d);
1586       break;
1587     case CEED_GAUSS_LOBATTO:
1588       ierr = CeedLobattoQuadrature(Q, q_ref_1d, q_weight_1d);
1589       break;
1590   }
1591   if (ierr != CEED_ERROR_SUCCESS) goto cleanup;
1592 
1593   // Build B, D matrix
1594   // Fornberg, 1998
1595   for (CeedInt i = 0; i < Q; i++) {
1596     c1                   = 1.0;
1597     c3                   = nodes[0] - q_ref_1d[i];
1598     interp_1d[i * P + 0] = 1.0;
1599     for (CeedInt j = 1; j < P; j++) {
1600       c2 = 1.0;
1601       c4 = c3;
1602       c3 = nodes[j] - q_ref_1d[i];
1603       for (CeedInt k = 0; k < j; k++) {
1604         dx = nodes[j] - nodes[k];
1605         c2 *= dx;
1606         if (k == j - 1) {
1607           grad_1d[i * P + j]   = c1 * (interp_1d[i * P + k] - c4 * grad_1d[i * P + k]) / c2;
1608           interp_1d[i * P + j] = -c1 * c4 * interp_1d[i * P + k] / c2;
1609         }
1610         grad_1d[i * P + k]   = (c3 * grad_1d[i * P + k] - interp_1d[i * P + k]) / dx;
1611         interp_1d[i * P + k] = c3 * interp_1d[i * P + k] / dx;
1612       }
1613       c1 = c2;
1614     }
1615   }
1616   // Pass to CeedBasisCreateTensorH1
1617   CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P, Q, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1618 cleanup:
1619   CeedCall(CeedFree(&interp_1d));
1620   CeedCall(CeedFree(&grad_1d));
1621   CeedCall(CeedFree(&nodes));
1622   CeedCall(CeedFree(&q_ref_1d));
1623   CeedCall(CeedFree(&q_weight_1d));
1624   return CEED_ERROR_SUCCESS;
1625 }
1626 
1627 /**
1628   @brief Create a non tensor-product basis for \f$H^1\f$ discretizations
1629 
1630   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1631   @param[in]  topo      Topology of element, e.g. hypercube, simplex, etc
1632   @param[in]  num_comp  Number of field components (1 for scalar fields)
1633   @param[in]  num_nodes Total number of nodes
1634   @param[in]  num_qpts  Total number of quadrature points
1635   @param[in]  interp    Row-major (`num_qpts * num_nodes`) matrix expressing the values of nodal basis functions at quadrature points
1636   @param[in]  grad      Row-major (`dim * num_qpts * num_nodes`) matrix expressing derivatives of nodal basis functions at quadrature points
1637   @param[in]  q_ref     Array of length `num_qpts * dim` holding the locations of quadrature points on the reference element
1638   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1639   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1640 
1641   @return An error code: 0 - success, otherwise - failure
1642 
1643   @ref User
1644 **/
1645 int CeedBasisCreateH1(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1646                       const CeedScalar *grad, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1647   CeedInt P = num_nodes, Q = num_qpts, dim = 0;
1648 
1649   if (!ceed->BasisCreateH1) {
1650     Ceed delegate;
1651 
1652     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1653     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateH1");
1654     CeedCall(CeedBasisCreateH1(delegate, topo, num_comp, num_nodes, num_qpts, interp, grad, q_ref, q_weight, basis));
1655     CeedCall(CeedDestroy(&delegate));
1656     return CEED_ERROR_SUCCESS;
1657   }
1658 
1659   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1660   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1661   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1662 
1663   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1664 
1665   CeedCall(CeedCalloc(1, basis));
1666   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1667   (*basis)->ref_count       = 1;
1668   (*basis)->is_tensor_basis = false;
1669   (*basis)->dim             = dim;
1670   (*basis)->topo            = topo;
1671   (*basis)->num_comp        = num_comp;
1672   (*basis)->P               = P;
1673   (*basis)->Q               = Q;
1674   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1675   CeedCall(CeedCalloc(Q * dim, &(*basis)->q_ref_1d));
1676   CeedCall(CeedCalloc(Q, &(*basis)->q_weight_1d));
1677   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1678   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1679   CeedCall(CeedCalloc(Q * P, &(*basis)->interp));
1680   CeedCall(CeedCalloc(dim * Q * P, &(*basis)->grad));
1681   if (interp) memcpy((*basis)->interp, interp, Q * P * sizeof(interp[0]));
1682   if (grad) memcpy((*basis)->grad, grad, dim * Q * P * sizeof(grad[0]));
1683   CeedCall(ceed->BasisCreateH1(topo, dim, P, Q, interp, grad, q_ref, q_weight, *basis));
1684   return CEED_ERROR_SUCCESS;
1685 }
1686 
1687 /**
1688   @brief Create a non tensor-product basis for \f$H(\mathrm{div})\f$ discretizations
1689 
1690   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1691   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1692   @param[in]  num_comp  Number of components (usually 1 for vectors in H(div) bases)
1693   @param[in]  num_nodes Total number of nodes (DoFs per element)
1694   @param[in]  num_qpts  Total number of quadrature points
1695   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1696   @param[in]  div       Row-major (`num_qpts * num_nodes`) matrix expressing divergence of basis functions at quadrature points
1697   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1698   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1699   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1700 
1701   @return An error code: 0 - success, otherwise - failure
1702 
1703   @ref User
1704 **/
1705 int CeedBasisCreateHdiv(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1706                         const CeedScalar *div, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1707   CeedInt Q = num_qpts, P = num_nodes, dim = 0;
1708 
1709   if (!ceed->BasisCreateHdiv) {
1710     Ceed delegate;
1711 
1712     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1713     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHdiv");
1714     CeedCall(CeedBasisCreateHdiv(delegate, topo, num_comp, num_nodes, num_qpts, interp, div, q_ref, q_weight, basis));
1715     CeedCall(CeedDestroy(&delegate));
1716     return CEED_ERROR_SUCCESS;
1717   }
1718 
1719   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1720   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1721   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1722 
1723   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1724 
1725   CeedCall(CeedCalloc(1, basis));
1726   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1727   (*basis)->ref_count       = 1;
1728   (*basis)->is_tensor_basis = false;
1729   (*basis)->dim             = dim;
1730   (*basis)->topo            = topo;
1731   (*basis)->num_comp        = num_comp;
1732   (*basis)->P               = P;
1733   (*basis)->Q               = Q;
1734   (*basis)->fe_space        = CEED_FE_SPACE_HDIV;
1735   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1736   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1737   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1738   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1739   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1740   CeedCall(CeedMalloc(Q * P, &(*basis)->div));
1741   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1742   if (div) memcpy((*basis)->div, div, Q * P * sizeof(div[0]));
1743   CeedCall(ceed->BasisCreateHdiv(topo, dim, P, Q, interp, div, q_ref, q_weight, *basis));
1744   return CEED_ERROR_SUCCESS;
1745 }
1746 
1747 /**
1748   @brief Create a non tensor-product basis for \f$H(\mathrm{curl})\f$ discretizations
1749 
1750   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1751   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1752   @param[in]  num_comp  Number of components (usually 1 for vectors in \f$H(\mathrm{curl})\f$ bases)
1753   @param[in]  num_nodes Total number of nodes (DoFs per element)
1754   @param[in]  num_qpts  Total number of quadrature points
1755   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1756   @param[in]  curl      Row-major (`curl_comp * num_qpts * num_nodes`, `curl_comp = 1` if `dim < 3` otherwise `curl_comp = dim`) matrix expressing curl of basis functions at quadrature points
1757   @param[in]  q_ref     Array of length `num_qpts * dim` holding the locations of quadrature points on the reference element
1758   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1759   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1760 
1761   @return An error code: 0 - success, otherwise - failure
1762 
1763   @ref User
1764 **/
1765 int CeedBasisCreateHcurl(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1766                          const CeedScalar *curl, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1767   CeedInt Q = num_qpts, P = num_nodes, dim = 0, curl_comp = 0;
1768 
1769   if (!ceed->BasisCreateHcurl) {
1770     Ceed delegate;
1771 
1772     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1773     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHcurl");
1774     CeedCall(CeedBasisCreateHcurl(delegate, topo, num_comp, num_nodes, num_qpts, interp, curl, q_ref, q_weight, basis));
1775     CeedCall(CeedDestroy(&delegate));
1776     return CEED_ERROR_SUCCESS;
1777   }
1778 
1779   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1780   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1781   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1782 
1783   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1784   curl_comp = (dim < 3) ? 1 : dim;
1785 
1786   CeedCall(CeedCalloc(1, basis));
1787   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1788   (*basis)->ref_count       = 1;
1789   (*basis)->is_tensor_basis = false;
1790   (*basis)->dim             = dim;
1791   (*basis)->topo            = topo;
1792   (*basis)->num_comp        = num_comp;
1793   (*basis)->P               = P;
1794   (*basis)->Q               = Q;
1795   (*basis)->fe_space        = CEED_FE_SPACE_HCURL;
1796   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1797   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1798   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1799   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1800   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1801   CeedCall(CeedMalloc(curl_comp * Q * P, &(*basis)->curl));
1802   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1803   if (curl) memcpy((*basis)->curl, curl, curl_comp * Q * P * sizeof(curl[0]));
1804   CeedCall(ceed->BasisCreateHcurl(topo, dim, P, Q, interp, curl, q_ref, q_weight, *basis));
1805   return CEED_ERROR_SUCCESS;
1806 }
1807 
1808 /**
1809   @brief Create a `CeedBasis` for projection from the nodes of `basis_from` to the nodes of `basis_to`.
1810 
1811   Only @ref CEED_EVAL_INTERP will be valid for the new basis, `basis_project`.
1812   For \f$H^1\f$ spaces, @ref CEED_EVAL_GRAD will also be valid.
1813   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
1814   The gradient (for the \f$H^1\f$ case) is given by `grad_project = interp_to^+ * grad_from`.
1815 
1816   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
1817 
1818   Note: `basis_project` will have the same number of components as `basis_from`, regardless of the number of components that `basis_to` has.
1819         If `basis_from` has 3 components and `basis_to` has 5 components, then `basis_project` will have 3 components.
1820 
1821   Note: If either `basis_from` or `basis_to` are non-tensor, then `basis_project` will also be non-tensor
1822 
1823   @param[in]  basis_from    `CeedBasis` to prolong from
1824   @param[in]  basis_to      `CeedBasis` to prolong to
1825   @param[out] basis_project Address of the variable where the newly created `CeedBasis` will be stored
1826 
1827   @return An error code: 0 - success, otherwise - failure
1828 
1829   @ref User
1830 **/
1831 int CeedBasisCreateProjection(CeedBasis basis_from, CeedBasis basis_to, CeedBasis *basis_project) {
1832   Ceed        ceed;
1833   bool        create_tensor;
1834   CeedInt     dim, num_comp;
1835   CeedScalar *interp_project, *grad_project;
1836 
1837   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
1838 
1839   // Create projection matrix
1840   CeedCall(CeedBasisCreateProjectionMatrices(basis_from, basis_to, &interp_project, &grad_project));
1841 
1842   // Build basis
1843   {
1844     bool is_tensor_to, is_tensor_from;
1845 
1846     CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
1847     CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
1848     create_tensor = is_tensor_from && is_tensor_to;
1849   }
1850   CeedCall(CeedBasisGetDimension(basis_to, &dim));
1851   CeedCall(CeedBasisGetNumComponents(basis_from, &num_comp));
1852   if (create_tensor) {
1853     CeedInt P_1d_to, P_1d_from;
1854 
1855     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_1d_from));
1856     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_1d_to));
1857     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d_from, P_1d_to, interp_project, grad_project, NULL, NULL, basis_project));
1858   } else {
1859     // Even if basis_to and basis_from are not H1, the resulting basis is H1 for interpolation to work
1860     CeedInt          num_nodes_to, num_nodes_from;
1861     CeedElemTopology topo;
1862 
1863     CeedCall(CeedBasisGetTopology(basis_from, &topo));
1864     CeedCall(CeedBasisGetNumNodes(basis_from, &num_nodes_from));
1865     CeedCall(CeedBasisGetNumNodes(basis_to, &num_nodes_to));
1866     CeedCall(CeedBasisCreateH1(ceed, topo, num_comp, num_nodes_from, num_nodes_to, interp_project, grad_project, NULL, NULL, basis_project));
1867   }
1868 
1869   // Cleanup
1870   CeedCall(CeedFree(&interp_project));
1871   CeedCall(CeedFree(&grad_project));
1872   CeedCall(CeedDestroy(&ceed));
1873   return CEED_ERROR_SUCCESS;
1874 }
1875 
1876 /**
1877   @brief Copy the pointer to a `CeedBasis`.
1878 
1879   Note: If the value of `*basis_copy` passed into this function is non-`NULL`, then it is assumed that `*basis_copy` is a pointer to a `CeedBasis`.
1880         This `CeedBasis` will be destroyed if `*basis_copy` is the only reference to this `CeedBasis`.
1881 
1882   @param[in]     basis      `CeedBasis` to copy reference to
1883   @param[in,out] basis_copy Variable to store copied reference
1884 
1885   @return An error code: 0 - success, otherwise - failure
1886 
1887   @ref User
1888 **/
1889 int CeedBasisReferenceCopy(CeedBasis basis, CeedBasis *basis_copy) {
1890   if (basis != CEED_BASIS_NONE) CeedCall(CeedBasisReference(basis));
1891   CeedCall(CeedBasisDestroy(basis_copy));
1892   *basis_copy = basis;
1893   return CEED_ERROR_SUCCESS;
1894 }
1895 
1896 /**
1897   @brief Set the number of tabs to indent for @ref CeedBasisView() output
1898 
1899   @param[in] basis    `CeedBasis` to set the number of view tabs
1900   @param[in] num_tabs Number of view tabs to set
1901 
1902   @return Error code: 0 - success, otherwise - failure
1903 
1904   @ref User
1905 **/
1906 int CeedBasisSetNumViewTabs(CeedBasis basis, CeedInt num_tabs) {
1907   CeedCheck(num_tabs >= 0, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Number of view tabs must be non-negative");
1908   basis->num_tabs = num_tabs;
1909   return CEED_ERROR_SUCCESS;
1910 }
1911 
1912 /**
1913   @brief Get the number of tabs to indent for @ref CeedBasisView() output
1914 
1915   @param[in]  basis    `CeedBasis` to get the number of view tabs
1916   @param[out] num_tabs Number of view tabs
1917 
1918   @return Error code: 0 - success, otherwise - failure
1919 
1920   @ref User
1921 **/
1922 int CeedBasisGetNumViewTabs(CeedBasis basis, CeedInt *num_tabs) {
1923   *num_tabs = basis->num_tabs;
1924   return CEED_ERROR_SUCCESS;
1925 }
1926 
1927 /**
1928   @brief View a `CeedBasis`
1929 
1930   @param[in] basis  `CeedBasis` to view
1931   @param[in] stream Stream to view to, e.g., `stdout`
1932 
1933   @return An error code: 0 - success, otherwise - failure
1934 
1935   @ref User
1936 **/
1937 int CeedBasisView(CeedBasis basis, FILE *stream) {
1938   bool             is_tensor_basis;
1939   char            *tabs = NULL;
1940   CeedElemTopology topo;
1941   CeedFESpace      fe_space;
1942 
1943   // Basis data
1944   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
1945   CeedCall(CeedBasisGetTopology(basis, &topo));
1946   CeedCall(CeedBasisGetFESpace(basis, &fe_space));
1947 
1948   {
1949     CeedInt num_tabs = 0;
1950 
1951     CeedCall(CeedBasisGetNumViewTabs(basis, &num_tabs));
1952     CeedCall(CeedCalloc(CEED_TAB_WIDTH * num_tabs + 1, &tabs));
1953     for (CeedInt i = 0; i < CEED_TAB_WIDTH * num_tabs; i++) tabs[i] = ' ';
1954   }
1955 
1956   // Print FE space and element topology of the basis
1957   fprintf(stream, "%sCeedBasis in a %s on a %s element\n", tabs, CeedFESpaces[fe_space], CeedElemTopologies[topo]);
1958   if (is_tensor_basis) {
1959     fprintf(stream, "%s  P: %" CeedInt_FMT "\n%s  Q: %" CeedInt_FMT "\n", tabs, basis->P_1d, tabs, basis->Q_1d);
1960   } else {
1961     fprintf(stream, "%s  P: %" CeedInt_FMT "\n%s  Q: %" CeedInt_FMT "\n", tabs, basis->P, tabs, basis->Q);
1962   }
1963   fprintf(stream, "%s  dimension: %" CeedInt_FMT "\n%s  field components: %" CeedInt_FMT "\n", tabs, basis->dim, tabs, basis->num_comp);
1964   // Print quadrature data, interpolation/gradient/divergence/curl of the basis
1965   if (is_tensor_basis) {  // tensor basis
1966     CeedInt           P_1d, Q_1d;
1967     const CeedScalar *q_ref_1d, *q_weight_1d, *interp_1d, *grad_1d;
1968 
1969     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
1970     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
1971     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
1972     CeedCall(CeedBasisGetQWeights(basis, &q_weight_1d));
1973     CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
1974     CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
1975 
1976     CeedCall(CeedScalarView("qref1d", "\t% 12.8f", 1, Q_1d, q_ref_1d, tabs, stream));
1977     CeedCall(CeedScalarView("qweight1d", "\t% 12.8f", 1, Q_1d, q_weight_1d, tabs, stream));
1978     CeedCall(CeedScalarView("interp1d", "\t% 12.8f", Q_1d, P_1d, interp_1d, tabs, stream));
1979     CeedCall(CeedScalarView("grad1d", "\t% 12.8f", Q_1d, P_1d, grad_1d, tabs, stream));
1980   } else {  // non-tensor basis
1981     CeedInt           P, Q, dim, q_comp;
1982     const CeedScalar *q_ref, *q_weight, *interp, *grad, *div, *curl;
1983 
1984     CeedCall(CeedBasisGetNumNodes(basis, &P));
1985     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &Q));
1986     CeedCall(CeedBasisGetDimension(basis, &dim));
1987     CeedCall(CeedBasisGetQRef(basis, &q_ref));
1988     CeedCall(CeedBasisGetQWeights(basis, &q_weight));
1989     CeedCall(CeedBasisGetInterp(basis, &interp));
1990     CeedCall(CeedBasisGetGrad(basis, &grad));
1991     CeedCall(CeedBasisGetDiv(basis, &div));
1992     CeedCall(CeedBasisGetCurl(basis, &curl));
1993 
1994     CeedCall(CeedScalarView("qref", "\t% 12.8f", 1, Q * dim, q_ref, tabs, stream));
1995     CeedCall(CeedScalarView("qweight", "\t% 12.8f", 1, Q, q_weight, tabs, stream));
1996     CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_INTERP, &q_comp));
1997     CeedCall(CeedScalarView("interp", "\t% 12.8f", q_comp * Q, P, interp, tabs, stream));
1998     if (grad) {
1999       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_GRAD, &q_comp));
2000       CeedCall(CeedScalarView("grad", "\t% 12.8f", q_comp * Q, P, grad, tabs, stream));
2001     }
2002     if (div) {
2003       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_DIV, &q_comp));
2004       CeedCall(CeedScalarView("div", "\t% 12.8f", q_comp * Q, P, div, tabs, stream));
2005     }
2006     if (curl) {
2007       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_CURL, &q_comp));
2008       CeedCall(CeedScalarView("curl", "\t% 12.8f", q_comp * Q, P, curl, tabs, stream));
2009     }
2010   }
2011   CeedCall(CeedFree(&tabs));
2012   return CEED_ERROR_SUCCESS;
2013 }
2014 
2015 /**
2016   @brief Apply basis evaluation from nodes to quadrature points or vice versa
2017 
2018   @param[in]  basis     `CeedBasis` to evaluate
2019   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
2020                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
2021   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
2022                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
2023   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
2024                           @ref CEED_EVAL_INTERP to use interpolated values,
2025                           @ref CEED_EVAL_GRAD to use gradients,
2026                           @ref CEED_EVAL_DIV to use divergence,
2027                           @ref CEED_EVAL_CURL to use curl,
2028                           @ref CEED_EVAL_WEIGHT to use quadrature weights
2029   @param[in]  u         Input `CeedVector`
2030   @param[out] v         Output `CeedVector`
2031 
2032   @return An error code: 0 - success, otherwise - failure
2033 
2034   @ref User
2035 **/
2036 int CeedBasisApply(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
2037   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
2038   CeedCheck(basis->Apply, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not support CeedBasisApply");
2039   CeedCall(basis->Apply(basis, num_elem, t_mode, eval_mode, u, v));
2040   return CEED_ERROR_SUCCESS;
2041 }
2042 
2043 /**
2044   @brief Apply basis evaluation from quadrature points to nodes and sum into target vector
2045 
2046   @param[in]  basis     `CeedBasis` to evaluate
2047   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
2048                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
2049   @param[in]  t_mode    @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes;
2050                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAdd()`
2051   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
2052                           @ref CEED_EVAL_INTERP to use interpolated values,
2053                           @ref CEED_EVAL_GRAD to use gradients,
2054                           @ref CEED_EVAL_DIV to use divergence,
2055                           @ref CEED_EVAL_CURL to use curl,
2056                           @ref CEED_EVAL_WEIGHT to use quadrature weights
2057   @param[in]  u         Input `CeedVector`
2058   @param[out] v         Output `CeedVector` to sum into
2059 
2060   @return An error code: 0 - success, otherwise - failure
2061 
2062   @ref User
2063 **/
2064 int CeedBasisApplyAdd(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
2065   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAdd only supports CEED_TRANSPOSE");
2066   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
2067   CeedCheck(basis->ApplyAdd, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not implement CeedBasisApplyAdd");
2068   CeedCall(basis->ApplyAdd(basis, num_elem, t_mode, eval_mode, u, v));
2069   return CEED_ERROR_SUCCESS;
2070 }
2071 
2072 /**
2073   @brief Apply basis evaluation from nodes to arbitrary points
2074 
2075   @param[in]  basis      `CeedBasis` to evaluate
2076   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
2077                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
2078   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
2079   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
2080                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
2081   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
2082                            @ref CEED_EVAL_GRAD to use gradients,
2083                            @ref CEED_EVAL_WEIGHT to use quadrature weights
2084   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
2085   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
2086   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
2087 
2088   @return An error code: 0 - success, otherwise - failure
2089 
2090   @ref User
2091 **/
2092 int CeedBasisApplyAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
2093                            CeedVector x_ref, CeedVector u, CeedVector v) {
2094   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
2095   if (basis->ApplyAtPoints) {
2096     CeedCall(basis->ApplyAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
2097   } else {
2098     CeedCall(CeedBasisApplyAtPoints_Core(basis, false, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
2099   }
2100   return CEED_ERROR_SUCCESS;
2101 }
2102 
2103 /**
2104   @brief Apply basis evaluation from nodes to arbitrary points and sum into target vector
2105 
2106   @param[in]  basis      `CeedBasis` to evaluate
2107   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
2108                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
2109   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
2110   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
2111                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAddAtPoints()`
2112   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
2113                            @ref CEED_EVAL_GRAD to use gradients,
2114                            @ref CEED_EVAL_WEIGHT to use quadrature weights
2115   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
2116   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
2117   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
2118 
2119   @return An error code: 0 - success, otherwise - failure
2120 
2121   @ref User
2122 **/
2123 int CeedBasisApplyAddAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
2124                               CeedVector x_ref, CeedVector u, CeedVector v) {
2125   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAddAtPoints only supports CEED_TRANSPOSE");
2126   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
2127   if (basis->ApplyAddAtPoints) {
2128     CeedCall(basis->ApplyAddAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
2129   } else {
2130     CeedCall(CeedBasisApplyAtPoints_Core(basis, true, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
2131   }
2132   return CEED_ERROR_SUCCESS;
2133 }
2134 
2135 /**
2136   @brief Get the `Ceed` associated with a `CeedBasis`
2137 
2138   @param[in]  basis `CeedBasis`
2139   @param[out] ceed  Variable to store `Ceed`
2140 
2141   @return An error code: 0 - success, otherwise - failure
2142 
2143   @ref Advanced
2144 **/
2145 int CeedBasisGetCeed(CeedBasis basis, Ceed *ceed) {
2146   *ceed = NULL;
2147   CeedCall(CeedReferenceCopy(CeedBasisReturnCeed(basis), ceed));
2148   return CEED_ERROR_SUCCESS;
2149 }
2150 
2151 /**
2152   @brief Return the `Ceed` associated with a `CeedBasis`
2153 
2154   @param[in]  basis `CeedBasis`
2155 
2156   @return `Ceed` associated with the `basis`
2157 
2158   @ref Advanced
2159 **/
2160 Ceed CeedBasisReturnCeed(CeedBasis basis) { return basis->ceed; }
2161 
2162 /**
2163   @brief Get dimension for given `CeedBasis`
2164 
2165   @param[in]  basis `CeedBasis`
2166   @param[out] dim   Variable to store dimension of basis
2167 
2168   @return An error code: 0 - success, otherwise - failure
2169 
2170   @ref Advanced
2171 **/
2172 int CeedBasisGetDimension(CeedBasis basis, CeedInt *dim) {
2173   *dim = basis->dim;
2174   return CEED_ERROR_SUCCESS;
2175 }
2176 
2177 /**
2178   @brief Get topology for given `CeedBasis`
2179 
2180   @param[in]  basis `CeedBasis`
2181   @param[out] topo  Variable to store topology of basis
2182 
2183   @return An error code: 0 - success, otherwise - failure
2184 
2185   @ref Advanced
2186 **/
2187 int CeedBasisGetTopology(CeedBasis basis, CeedElemTopology *topo) {
2188   *topo = basis->topo;
2189   return CEED_ERROR_SUCCESS;
2190 }
2191 
2192 /**
2193   @brief Get number of components for given `CeedBasis`
2194 
2195   @param[in]  basis    `CeedBasis`
2196   @param[out] num_comp Variable to store number of components
2197 
2198   @return An error code: 0 - success, otherwise - failure
2199 
2200   @ref Advanced
2201 **/
2202 int CeedBasisGetNumComponents(CeedBasis basis, CeedInt *num_comp) {
2203   *num_comp = basis->num_comp;
2204   return CEED_ERROR_SUCCESS;
2205 }
2206 
2207 /**
2208   @brief Get total number of nodes (in `dim` dimensions) of a `CeedBasis`
2209 
2210   @param[in]  basis `CeedBasis`
2211   @param[out] P     Variable to store number of nodes
2212 
2213   @return An error code: 0 - success, otherwise - failure
2214 
2215   @ref Utility
2216 **/
2217 int CeedBasisGetNumNodes(CeedBasis basis, CeedInt *P) {
2218   *P = basis->P;
2219   return CEED_ERROR_SUCCESS;
2220 }
2221 
2222 /**
2223   @brief Get total number of nodes (in 1 dimension) of a `CeedBasis`
2224 
2225   @param[in]  basis `CeedBasis`
2226   @param[out] P_1d  Variable to store number of nodes
2227 
2228   @return An error code: 0 - success, otherwise - failure
2229 
2230   @ref Advanced
2231 **/
2232 int CeedBasisGetNumNodes1D(CeedBasis basis, CeedInt *P_1d) {
2233   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply P_1d for non-tensor CeedBasis");
2234   *P_1d = basis->P_1d;
2235   return CEED_ERROR_SUCCESS;
2236 }
2237 
2238 /**
2239   @brief Get total number of quadrature points (in `dim` dimensions) of a `CeedBasis`
2240 
2241   @param[in]  basis `CeedBasis`
2242   @param[out] Q     Variable to store number of quadrature points
2243 
2244   @return An error code: 0 - success, otherwise - failure
2245 
2246   @ref Utility
2247 **/
2248 int CeedBasisGetNumQuadraturePoints(CeedBasis basis, CeedInt *Q) {
2249   *Q = basis->Q;
2250   return CEED_ERROR_SUCCESS;
2251 }
2252 
2253 /**
2254   @brief Get total number of quadrature points (in 1 dimension) of a `CeedBasis`
2255 
2256   @param[in]  basis `CeedBasis`
2257   @param[out] Q_1d  Variable to store number of quadrature points
2258 
2259   @return An error code: 0 - success, otherwise - failure
2260 
2261   @ref Advanced
2262 **/
2263 int CeedBasisGetNumQuadraturePoints1D(CeedBasis basis, CeedInt *Q_1d) {
2264   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply Q_1d for non-tensor CeedBasis");
2265   *Q_1d = basis->Q_1d;
2266   return CEED_ERROR_SUCCESS;
2267 }
2268 
2269 /**
2270   @brief Get reference coordinates of quadrature points (in `dim` dimensions) of a `CeedBasis`
2271 
2272   @param[in]  basis `CeedBasis`
2273   @param[out] q_ref Variable to store reference coordinates of quadrature points
2274 
2275   @return An error code: 0 - success, otherwise - failure
2276 
2277   @ref Advanced
2278 **/
2279 int CeedBasisGetQRef(CeedBasis basis, const CeedScalar **q_ref) {
2280   *q_ref = basis->q_ref_1d;
2281   return CEED_ERROR_SUCCESS;
2282 }
2283 
2284 /**
2285   @brief Get quadrature weights of quadrature points (in `dim` dimensions) of a `CeedBasis`
2286 
2287   @param[in]  basis    `CeedBasis`
2288   @param[out] q_weight Variable to store quadrature weights
2289 
2290   @return An error code: 0 - success, otherwise - failure
2291 
2292   @ref Advanced
2293 **/
2294 int CeedBasisGetQWeights(CeedBasis basis, const CeedScalar **q_weight) {
2295   *q_weight = basis->q_weight_1d;
2296   return CEED_ERROR_SUCCESS;
2297 }
2298 
2299 /**
2300   @brief Get interpolation matrix of a `CeedBasis`
2301 
2302   @param[in]  basis  `CeedBasis`
2303   @param[out] interp Variable to store interpolation matrix
2304 
2305   @return An error code: 0 - success, otherwise - failure
2306 
2307   @ref Advanced
2308 **/
2309 int CeedBasisGetInterp(CeedBasis basis, const CeedScalar **interp) {
2310   if (!basis->interp && basis->is_tensor_basis) {
2311     // Allocate
2312     CeedCall(CeedMalloc(basis->Q * basis->P, &basis->interp));
2313 
2314     // Initialize
2315     for (CeedInt i = 0; i < basis->Q * basis->P; i++) basis->interp[i] = 1.0;
2316 
2317     // Calculate
2318     for (CeedInt d = 0; d < basis->dim; d++) {
2319       for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2320         for (CeedInt node = 0; node < basis->P; node++) {
2321           CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2322           CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2323 
2324           basis->interp[qpt * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2325         }
2326       }
2327     }
2328   }
2329   *interp = basis->interp;
2330   return CEED_ERROR_SUCCESS;
2331 }
2332 
2333 /**
2334   @brief Get 1D interpolation matrix of a tensor product `CeedBasis`
2335 
2336   @param[in]  basis     `CeedBasis`
2337   @param[out] interp_1d Variable to store interpolation matrix
2338 
2339   @return An error code: 0 - success, otherwise - failure
2340 
2341   @ref Backend
2342 **/
2343 int CeedBasisGetInterp1D(CeedBasis basis, const CeedScalar **interp_1d) {
2344   bool is_tensor_basis;
2345 
2346   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2347   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2348   *interp_1d = basis->interp_1d;
2349   return CEED_ERROR_SUCCESS;
2350 }
2351 
2352 /**
2353   @brief Get gradient matrix of a `CeedBasis`
2354 
2355   @param[in]  basis `CeedBasis`
2356   @param[out] grad  Variable to store gradient matrix
2357 
2358   @return An error code: 0 - success, otherwise - failure
2359 
2360   @ref Advanced
2361 **/
2362 int CeedBasisGetGrad(CeedBasis basis, const CeedScalar **grad) {
2363   if (!basis->grad && basis->is_tensor_basis) {
2364     // Allocate
2365     CeedCall(CeedMalloc(basis->dim * basis->Q * basis->P, &basis->grad));
2366 
2367     // Initialize
2368     for (CeedInt i = 0; i < basis->dim * basis->Q * basis->P; i++) basis->grad[i] = 1.0;
2369 
2370     // Calculate
2371     for (CeedInt d = 0; d < basis->dim; d++) {
2372       for (CeedInt i = 0; i < basis->dim; i++) {
2373         for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2374           for (CeedInt node = 0; node < basis->P; node++) {
2375             CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2376             CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2377 
2378             if (i == d) basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->grad_1d[q * basis->P_1d + p];
2379             else basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2380           }
2381         }
2382       }
2383     }
2384   }
2385   *grad = basis->grad;
2386   return CEED_ERROR_SUCCESS;
2387 }
2388 
2389 /**
2390   @brief Get 1D gradient matrix of a tensor product `CeedBasis`
2391 
2392   @param[in]  basis   `CeedBasis`
2393   @param[out] grad_1d Variable to store gradient matrix
2394 
2395   @return An error code: 0 - success, otherwise - failure
2396 
2397   @ref Advanced
2398 **/
2399 int CeedBasisGetGrad1D(CeedBasis basis, const CeedScalar **grad_1d) {
2400   bool is_tensor_basis;
2401 
2402   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2403   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2404   *grad_1d = basis->grad_1d;
2405   return CEED_ERROR_SUCCESS;
2406 }
2407 
2408 /**
2409   @brief Get divergence matrix of a `CeedBasis`
2410 
2411   @param[in]  basis `CeedBasis`
2412   @param[out] div   Variable to store divergence matrix
2413 
2414   @return An error code: 0 - success, otherwise - failure
2415 
2416   @ref Advanced
2417 **/
2418 int CeedBasisGetDiv(CeedBasis basis, const CeedScalar **div) {
2419   *div = basis->div;
2420   return CEED_ERROR_SUCCESS;
2421 }
2422 
2423 /**
2424   @brief Get curl matrix of a `CeedBasis`
2425 
2426   @param[in]  basis `CeedBasis`
2427   @param[out] curl  Variable to store curl matrix
2428 
2429   @return An error code: 0 - success, otherwise - failure
2430 
2431   @ref Advanced
2432 **/
2433 int CeedBasisGetCurl(CeedBasis basis, const CeedScalar **curl) {
2434   *curl = basis->curl;
2435   return CEED_ERROR_SUCCESS;
2436 }
2437 
2438 /**
2439   @brief Destroy a @ref  CeedBasis
2440 
2441   @param[in,out] basis `CeedBasis` to destroy
2442 
2443   @return An error code: 0 - success, otherwise - failure
2444 
2445   @ref User
2446 **/
2447 int CeedBasisDestroy(CeedBasis *basis) {
2448   if (!*basis || *basis == CEED_BASIS_NONE || --(*basis)->ref_count > 0) {
2449     *basis = NULL;
2450     return CEED_ERROR_SUCCESS;
2451   }
2452   if ((*basis)->Destroy) CeedCall((*basis)->Destroy(*basis));
2453   CeedCall(CeedTensorContractDestroy(&(*basis)->contract));
2454   CeedCall(CeedFree(&(*basis)->q_ref_1d));
2455   CeedCall(CeedFree(&(*basis)->q_weight_1d));
2456   CeedCall(CeedFree(&(*basis)->interp));
2457   CeedCall(CeedFree(&(*basis)->interp_1d));
2458   CeedCall(CeedFree(&(*basis)->grad));
2459   CeedCall(CeedFree(&(*basis)->grad_1d));
2460   CeedCall(CeedFree(&(*basis)->div));
2461   CeedCall(CeedFree(&(*basis)->curl));
2462   CeedCall(CeedVectorDestroy(&(*basis)->vec_chebyshev));
2463   CeedCall(CeedBasisDestroy(&(*basis)->basis_chebyshev));
2464   CeedCall(CeedDestroy(&(*basis)->ceed));
2465   CeedCall(CeedFree(basis));
2466   return CEED_ERROR_SUCCESS;
2467 }
2468 
2469 /**
2470   @brief Construct a Gauss-Legendre quadrature
2471 
2472   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-1` exactly)
2473   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2474   @param[out] q_weight_1d Array of length `Q` to hold the weights
2475 
2476   @return An error code: 0 - success, otherwise - failure
2477 
2478   @ref Utility
2479 **/
2480 int CeedGaussQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2481   CeedScalar P0, P1, P2, dP2, xi, wi, PI = 4.0 * atan(1.0);
2482 
2483   // Build q_ref_1d, q_weight_1d
2484   for (CeedInt i = 0; i <= Q / 2; i++) {
2485     // Guess
2486     xi = cos(PI * (CeedScalar)(2 * i + 1) / ((CeedScalar)(2 * Q)));
2487     // Pn(xi)
2488     P0 = 1.0;
2489     P1 = xi;
2490     P2 = 0.0;
2491     for (CeedInt j = 2; j <= Q; j++) {
2492       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2493       P0 = P1;
2494       P1 = P2;
2495     }
2496     // First Newton Step
2497     dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2498     xi  = xi - P2 / dP2;
2499     // Newton to convergence
2500     for (CeedInt k = 0; k < 100 && fabs(P2) > 10 * CEED_EPSILON; k++) {
2501       P0 = 1.0;
2502       P1 = xi;
2503       for (CeedInt j = 2; j <= Q; j++) {
2504         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2505         P0 = P1;
2506         P1 = P2;
2507       }
2508       dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2509       xi  = xi - P2 / dP2;
2510     }
2511     // Save xi, wi
2512     wi                     = 2.0 / ((1.0 - xi * xi) * dP2 * dP2);
2513     q_weight_1d[i]         = wi;
2514     q_weight_1d[Q - 1 - i] = wi;
2515     q_ref_1d[i]            = -xi;
2516     q_ref_1d[Q - 1 - i]    = xi;
2517   }
2518   return CEED_ERROR_SUCCESS;
2519 }
2520 
2521 /**
2522   @brief Construct a Gauss-Legendre-Lobatto quadrature
2523 
2524   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-3` exactly)
2525   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2526   @param[out] q_weight_1d Array of length `Q` to hold the weights
2527 
2528   @return An error code: 0 - success, otherwise - failure
2529 
2530   @ref Utility
2531 **/
2532 int CeedLobattoQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2533   CeedScalar P0, P1, P2, dP2, d2P2, xi, wi, PI = 4.0 * atan(1.0);
2534 
2535   // Build q_ref_1d, q_weight_1d
2536   // Set endpoints
2537   CeedCheck(Q > 1, NULL, CEED_ERROR_DIMENSION, "Cannot create Lobatto quadrature with Q=%" CeedInt_FMT " < 2 points", Q);
2538   wi = 2.0 / ((CeedScalar)(Q * (Q - 1)));
2539   if (q_weight_1d) {
2540     q_weight_1d[0]     = wi;
2541     q_weight_1d[Q - 1] = wi;
2542   }
2543   q_ref_1d[0]     = -1.0;
2544   q_ref_1d[Q - 1] = 1.0;
2545   // Interior
2546   for (CeedInt i = 1; i <= (Q - 1) / 2; i++) {
2547     // Guess
2548     xi = cos(PI * (CeedScalar)(i) / (CeedScalar)(Q - 1));
2549     // Pn(xi)
2550     P0 = 1.0;
2551     P1 = xi;
2552     P2 = 0.0;
2553     for (CeedInt j = 2; j < Q; j++) {
2554       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2555       P0 = P1;
2556       P1 = P2;
2557     }
2558     // First Newton step
2559     dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2560     d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2561     xi   = xi - dP2 / d2P2;
2562     // Newton to convergence
2563     for (CeedInt k = 0; k < 100 && fabs(dP2) > 10 * CEED_EPSILON; k++) {
2564       P0 = 1.0;
2565       P1 = xi;
2566       for (CeedInt j = 2; j < Q; j++) {
2567         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2568         P0 = P1;
2569         P1 = P2;
2570       }
2571       dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2572       d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2573       xi   = xi - dP2 / d2P2;
2574     }
2575     // Save xi, wi
2576     wi = 2.0 / (((CeedScalar)(Q * (Q - 1))) * P2 * P2);
2577     if (q_weight_1d) {
2578       q_weight_1d[i]         = wi;
2579       q_weight_1d[Q - 1 - i] = wi;
2580     }
2581     q_ref_1d[i]         = -xi;
2582     q_ref_1d[Q - 1 - i] = xi;
2583   }
2584   return CEED_ERROR_SUCCESS;
2585 }
2586 
2587 /// @}
2588