xref: /libCEED/interface/ceed-basis.c (revision 3e961e14fcf6ad615ceece5f8606a32a7b6c0794)
1 // Copyright (c) 2017-2024, 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] stream Stream to view to, e.g., `stdout`
157 
158   @return An error code: 0 - success, otherwise - failure
159 
160   @ref Developer
161 **/
162 static int CeedScalarView(const char *name, const char *fp_fmt, CeedInt m, CeedInt n, const CeedScalar *a, FILE *stream) {
163   if (m > 1) {
164     fprintf(stream, "  %s:\n", name);
165   } else {
166     char padded_name[12];
167 
168     snprintf(padded_name, 11, "%s:", name);
169     fprintf(stream, "  %-10s", padded_name);
170   }
171   for (CeedInt i = 0; i < m; i++) {
172     if (m > 1) fprintf(stream, "    [%" CeedInt_FMT "]", i);
173     for (CeedInt j = 0; j < n; j++) fprintf(stream, fp_fmt, fabs(a[i * n + j]) > 1E-14 ? a[i * n + j] : 0);
174     fputs("\n", stream);
175   }
176   return CEED_ERROR_SUCCESS;
177 }
178 
179 /**
180   @brief Create the interpolation and gradient matrices for projection from the nodes of `basis_from` to the nodes of `basis_to`.
181 
182   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
183   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.
184 
185   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
186 
187   @param[in]  basis_from     `CeedBasis` to project from
188   @param[in]  basis_to       `CeedBasis` to project to
189   @param[out] interp_project Address of the variable where the newly created interpolation matrix will be stored
190   @param[out] grad_project   Address of the variable where the newly created gradient matrix will be stored
191 
192   @return An error code: 0 - success, otherwise - failure
193 
194   @ref Developer
195 **/
196 static int CeedBasisCreateProjectionMatrices(CeedBasis basis_from, CeedBasis basis_to, CeedScalar **interp_project, CeedScalar **grad_project) {
197   Ceed    ceed;
198   bool    are_both_tensor;
199   CeedInt Q, Q_to, Q_from, P_to, P_from;
200 
201   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
202 
203   // Check for compatible quadrature spaces
204   CeedCall(CeedBasisGetNumQuadraturePoints(basis_to, &Q_to));
205   CeedCall(CeedBasisGetNumQuadraturePoints(basis_from, &Q_from));
206   CeedCheck(Q_to == Q_from, ceed, CEED_ERROR_DIMENSION,
207             "Bases must have compatible quadrature spaces."
208             " 'basis_from' has %" CeedInt_FMT " points and 'basis_to' has %" CeedInt_FMT,
209             Q_from, Q_to);
210   Q = Q_to;
211 
212   // Check for matching tensor or non-tensor
213   {
214     bool is_tensor_to, is_tensor_from;
215 
216     CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
217     CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
218     are_both_tensor = is_tensor_to && is_tensor_from;
219   }
220   if (are_both_tensor) {
221     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_to));
222     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_from));
223     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis_from, &Q));
224   } else {
225     CeedCall(CeedBasisGetNumNodes(basis_to, &P_to));
226     CeedCall(CeedBasisGetNumNodes(basis_from, &P_from));
227   }
228 
229   // Check for matching FE space
230   CeedFESpace fe_space_to, fe_space_from;
231 
232   CeedCall(CeedBasisGetFESpace(basis_to, &fe_space_to));
233   CeedCall(CeedBasisGetFESpace(basis_from, &fe_space_from));
234   CeedCheck(fe_space_to == fe_space_from, ceed, CEED_ERROR_MINOR,
235             "Bases must both be the same FE space type."
236             " 'basis_from' is a %s and 'basis_to' is a %s",
237             CeedFESpaces[fe_space_from], CeedFESpaces[fe_space_to]);
238 
239   // Get source matrices
240   CeedInt           dim, q_comp = 1;
241   CeedScalar       *interp_to_inv, *interp_from;
242   const CeedScalar *interp_to_source = NULL, *interp_from_source = NULL, *grad_from_source = NULL;
243 
244   CeedCall(CeedBasisGetDimension(basis_from, &dim));
245   if (are_both_tensor) {
246     CeedCall(CeedBasisGetInterp1D(basis_to, &interp_to_source));
247     CeedCall(CeedBasisGetInterp1D(basis_from, &interp_from_source));
248   } else {
249     CeedCall(CeedBasisGetNumQuadratureComponents(basis_from, CEED_EVAL_INTERP, &q_comp));
250     CeedCall(CeedBasisGetInterp(basis_to, &interp_to_source));
251     CeedCall(CeedBasisGetInterp(basis_from, &interp_from_source));
252   }
253   CeedCall(CeedMalloc(Q * P_from * q_comp, &interp_from));
254   CeedCall(CeedCalloc(P_to * P_from, interp_project));
255 
256   // `grad_project = interp_to^+ * grad_from` is computed for the H^1 space case so the
257   // projection basis will have a gradient operation (allocated even if not H^1 for the
258   // basis construction later on)
259   if (fe_space_to == CEED_FE_SPACE_H1) {
260     if (are_both_tensor) {
261       CeedCall(CeedBasisGetGrad1D(basis_from, &grad_from_source));
262     } else {
263       CeedCall(CeedBasisGetGrad(basis_from, &grad_from_source));
264     }
265   }
266   CeedCall(CeedCalloc(P_to * P_from * (are_both_tensor ? 1 : dim), grad_project));
267 
268   // Compute interp_to^+, pseudoinverse of interp_to
269   CeedCall(CeedCalloc(Q * q_comp * P_to, &interp_to_inv));
270   CeedCall(CeedMatrixPseudoinverse(ceed, interp_to_source, Q * q_comp, P_to, interp_to_inv));
271   // Build matrices
272   CeedInt     num_matrices = 1 + (fe_space_to == CEED_FE_SPACE_H1) * (are_both_tensor ? 1 : dim);
273   CeedScalar *input_from[num_matrices], *output_project[num_matrices];
274 
275   input_from[0]     = (CeedScalar *)interp_from_source;
276   output_project[0] = *interp_project;
277   for (CeedInt m = 1; m < num_matrices; m++) {
278     input_from[m]     = (CeedScalar *)&grad_from_source[(m - 1) * Q * P_from];
279     output_project[m] = &((*grad_project)[(m - 1) * P_to * P_from]);
280   }
281   for (CeedInt m = 0; m < num_matrices; m++) {
282     // output_project = interp_to^+ * interp_from
283     memcpy(interp_from, input_from[m], Q * P_from * q_comp * sizeof(input_from[m][0]));
284     CeedCall(CeedMatrixMatrixMultiply(ceed, interp_to_inv, input_from[m], output_project[m], P_to, P_from, Q * q_comp));
285     // Round zero to machine precision
286     for (CeedInt i = 0; i < P_to * P_from; i++) {
287       if (fabs(output_project[m][i]) < 10 * CEED_EPSILON) output_project[m][i] = 0.0;
288     }
289   }
290 
291   // Cleanup
292   CeedCall(CeedFree(&interp_to_inv));
293   CeedCall(CeedFree(&interp_from));
294   return CEED_ERROR_SUCCESS;
295 }
296 
297 /**
298   @brief Check input vector dimensions for CeedBasisApply[Add]AtPoints
299 
300   @param[in]  basis      `CeedBasis` to evaluate
301   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
302                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
303   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
304   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
305                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
306   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
307                            @ref CEED_EVAL_GRAD to use gradients,
308                            @ref CEED_EVAL_WEIGHT to use quadrature weights
309   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
310   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
311   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
312 
313   @return An error code: 0 - success, otherwise - failure
314 
315   @ref Developer
316 **/
317 static int CeedBasisApplyAtPointsCheckDims(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode,
318                                            CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u, CeedVector v) {
319   CeedInt  dim, num_comp, num_q_comp, num_nodes, P_1d = 1, Q_1d = 1, total_num_points = 0;
320   CeedSize x_length = 0, u_length = 0, v_length;
321   Ceed     ceed;
322 
323   CeedCall(CeedBasisGetCeed(basis, &ceed));
324   CeedCall(CeedBasisGetDimension(basis, &dim));
325   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
326   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
327   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
328   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &num_q_comp));
329   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
330   CeedCall(CeedVectorGetLength(v, &v_length));
331   if (x_ref != CEED_VECTOR_NONE) CeedCall(CeedVectorGetLength(x_ref, &x_length));
332   if (u != CEED_VECTOR_NONE) CeedCall(CeedVectorGetLength(u, &u_length));
333 
334   // Check compatibility of topological and geometrical dimensions
335   CeedCheck((t_mode == CEED_TRANSPOSE && v_length % num_nodes == 0) || (t_mode == CEED_NOTRANSPOSE && u_length % num_nodes == 0) ||
336                 (eval_mode == CEED_EVAL_WEIGHT),
337             ceed, CEED_ERROR_DIMENSION, "Length of input/output vectors incompatible with basis dimensions and number of points");
338 
339   // Check compatibility coordinates vector
340   for (CeedInt i = 0; i < num_elem; i++) total_num_points += num_points[i];
341   CeedCheck((x_length >= total_num_points * dim) || (eval_mode == CEED_EVAL_WEIGHT), ceed, CEED_ERROR_DIMENSION,
342             "Length of reference coordinate vector incompatible with basis dimension and number of points."
343             " Found reference coordinate vector of length %" CeedSize_FMT ", not of length %" CeedSize_FMT ".",
344             x_length, total_num_points * dim);
345 
346   // Check CEED_EVAL_WEIGHT only on CEED_NOTRANSPOSE
347   CeedCheck(eval_mode != CEED_EVAL_WEIGHT || t_mode == CEED_NOTRANSPOSE, ceed, CEED_ERROR_UNSUPPORTED,
348             "CEED_EVAL_WEIGHT only supported with CEED_NOTRANSPOSE");
349 
350   // Check vector lengths to prevent out of bounds issues
351   bool has_good_dims = true;
352   switch (eval_mode) {
353     case CEED_EVAL_INTERP:
354       has_good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= total_num_points * num_q_comp || v_length >= num_elem * num_nodes * num_comp)) ||
355                        (t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points * num_q_comp || u_length >= num_elem * num_nodes * num_comp)));
356       break;
357     case CEED_EVAL_GRAD:
358       has_good_dims =
359           ((t_mode == CEED_TRANSPOSE && (u_length >= total_num_points * num_q_comp * dim || v_length >= num_elem * num_nodes * num_comp)) ||
360            (t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points * num_q_comp * dim || u_length >= num_elem * num_nodes * num_comp)));
361       break;
362     case CEED_EVAL_WEIGHT:
363       has_good_dims = t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points);
364       break;
365       // LCOV_EXCL_START
366     case CEED_EVAL_NONE:
367     case CEED_EVAL_DIV:
368     case CEED_EVAL_CURL:
369       return CeedError(ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points not supported for %s", CeedEvalModes[eval_mode]);
370       // LCOV_EXCL_STOP
371   }
372   CeedCheck(has_good_dims, ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
373   return CEED_ERROR_SUCCESS;
374 }
375 
376 /**
377   @brief Default implimentation to apply basis evaluation from nodes to arbitrary points
378 
379   @param[in]  basis      `CeedBasis` to evaluate
380   @param[in]  apply_add  Sum result into target vector or overwrite
381   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
382                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
383   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
384   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
385                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
386   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
387                            @ref CEED_EVAL_GRAD to use gradients,
388                            @ref CEED_EVAL_WEIGHT to use quadrature weights
389   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
390   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
391   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
392 
393   @return An error code: 0 - success, otherwise - failure
394 
395   @ref Developer
396 **/
397 static int CeedBasisApplyAtPoints_Core(CeedBasis basis, bool apply_add, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode,
398                                        CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u, CeedVector v) {
399   CeedInt dim, num_comp, P_1d = 1, Q_1d = 1, total_num_points = num_points[0];
400   Ceed    ceed;
401 
402   CeedCall(CeedBasisGetCeed(basis, &ceed));
403   CeedCall(CeedBasisGetDimension(basis, &dim));
404   // Inserting check because clang-tidy doesn't understand this cannot occur
405   CeedCheck(dim > 0, ceed, CEED_ERROR_UNSUPPORTED, "Malformed CeedBasis, dim > 0 is required");
406   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
407   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
408   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
409 
410   // Default implementation
411   {
412     bool is_tensor_basis;
413 
414     CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
415     CeedCheck(is_tensor_basis, ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points only supported for tensor product bases");
416   }
417   CeedCheck(num_elem == 1, ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary  points only supported for a single element at a time");
418   if (eval_mode == CEED_EVAL_WEIGHT) {
419     CeedCall(CeedVectorSetValue(v, 1.0));
420     return CEED_ERROR_SUCCESS;
421   }
422   if (!basis->basis_chebyshev) {
423     // Build basis mapping from nodes to Chebyshev coefficients
424     CeedScalar       *chebyshev_interp_1d, *chebyshev_grad_1d, *chebyshev_q_weight_1d;
425     const CeedScalar *q_ref_1d;
426 
427     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_interp_1d));
428     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_grad_1d));
429     CeedCall(CeedCalloc(Q_1d, &chebyshev_q_weight_1d));
430     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
431     CeedCall(CeedBasisGetChebyshevInterp1D(basis, chebyshev_interp_1d));
432 
433     CeedCall(CeedVectorCreate(ceed, num_comp * CeedIntPow(Q_1d, dim), &basis->vec_chebyshev));
434     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d, Q_1d, chebyshev_interp_1d, chebyshev_grad_1d, q_ref_1d, chebyshev_q_weight_1d,
435                                      &basis->basis_chebyshev));
436 
437     // Cleanup
438     CeedCall(CeedFree(&chebyshev_interp_1d));
439     CeedCall(CeedFree(&chebyshev_grad_1d));
440     CeedCall(CeedFree(&chebyshev_q_weight_1d));
441   }
442 
443   // Create TensorContract object if needed, such as a basis from the GPU backends
444   if (!basis->contract) {
445     Ceed      ceed_ref;
446     CeedBasis basis_ref = NULL;
447 
448     CeedCall(CeedInit("/cpu/self", &ceed_ref));
449     // Only need matching tensor contraction dimensions, any type of basis will work
450     CeedCall(CeedBasisCreateTensorH1Lagrange(ceed_ref, dim, num_comp, P_1d, Q_1d, CEED_GAUSS, &basis_ref));
451     // Note - clang-tidy doesn't know basis_ref->contract must be valid here
452     CeedCheck(basis_ref && basis_ref->contract, ceed, CEED_ERROR_UNSUPPORTED, "Reference CPU ceed failed to create a tensor contraction object");
453     CeedCall(CeedTensorContractReferenceCopy(basis_ref->contract, &basis->contract));
454     CeedCall(CeedBasisDestroy(&basis_ref));
455     CeedCall(CeedDestroy(&ceed_ref));
456   }
457 
458   // Basis evaluation
459   switch (t_mode) {
460     case CEED_NOTRANSPOSE: {
461       // Nodes to arbitrary points
462       CeedScalar       *v_array;
463       const CeedScalar *chebyshev_coeffs, *x_array_read;
464 
465       // -- Interpolate to Chebyshev coefficients
466       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_NOTRANSPOSE, CEED_EVAL_INTERP, u, basis->vec_chebyshev));
467 
468       // -- Evaluate Chebyshev polynomials at arbitrary points
469       CeedCall(CeedVectorGetArrayRead(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
470       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
471       CeedCall(CeedVectorGetArrayWrite(v, CEED_MEM_HOST, &v_array));
472       switch (eval_mode) {
473         case CEED_EVAL_INTERP: {
474           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
475 
476           // ---- Values at point
477           for (CeedInt p = 0; p < total_num_points; p++) {
478             CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
479 
480             for (CeedInt d = 0; d < dim; d++) {
481               // ------ Tensor contract with current Chebyshev polynomial values
482               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
483               CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
484                                                d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
485               pre /= Q_1d;
486               post *= 1;
487             }
488             for (CeedInt c = 0; c < num_comp; c++) v_array[c * total_num_points + p] = tmp[dim % 2][c];
489           }
490           break;
491         }
492         case CEED_EVAL_GRAD: {
493           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
494 
495           // ---- Values at point
496           for (CeedInt p = 0; p < total_num_points; p++) {
497             // Dim**2 contractions, apply grad when pass == dim
498             for (CeedInt pass = 0; pass < dim; pass++) {
499               CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
500 
501               for (CeedInt d = 0; d < dim; d++) {
502                 // ------ Tensor contract with current Chebyshev polynomial values
503                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
504                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
505                 CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
506                                                  d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
507                 pre /= Q_1d;
508                 post *= 1;
509               }
510               for (CeedInt c = 0; c < num_comp; c++) v_array[(pass * num_comp + c) * total_num_points + p] = tmp[dim % 2][c];
511             }
512           }
513           break;
514         }
515         default:
516           // Nothing to do, excluded above
517           break;
518       }
519       CeedCall(CeedVectorRestoreArrayRead(basis->vec_chebyshev, &chebyshev_coeffs));
520       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
521       CeedCall(CeedVectorRestoreArray(v, &v_array));
522       break;
523     }
524     case CEED_TRANSPOSE: {
525       // Note: No switch on e_mode here because only CEED_EVAL_INTERP is supported at this time
526       // Arbitrary points to nodes
527       CeedScalar       *chebyshev_coeffs;
528       const CeedScalar *u_array, *x_array_read;
529 
530       // -- Transpose of evaluation of Chebyshev polynomials at arbitrary points
531       CeedCall(CeedVectorGetArrayWrite(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
532       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
533       CeedCall(CeedVectorGetArrayRead(u, CEED_MEM_HOST, &u_array));
534 
535       switch (eval_mode) {
536         case CEED_EVAL_INTERP: {
537           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
538 
539           // ---- Values at point
540           for (CeedInt p = 0; p < total_num_points; p++) {
541             CeedInt pre = num_comp * 1, post = 1;
542 
543             for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[c * total_num_points + p];
544             for (CeedInt d = 0; d < dim; d++) {
545               // ------ Tensor contract with current Chebyshev polynomial values
546               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
547               CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode, p > 0 && d == (dim - 1), tmp[d % 2],
548                                                d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
549               pre /= 1;
550               post *= Q_1d;
551             }
552           }
553           break;
554         }
555         case CEED_EVAL_GRAD: {
556           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
557 
558           // ---- Values at point
559           for (CeedInt p = 0; p < total_num_points; p++) {
560             // Dim**2 contractions, apply grad when pass == dim
561             for (CeedInt pass = 0; pass < dim; pass++) {
562               CeedInt pre = num_comp * 1, post = 1;
563 
564               for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[(pass * num_comp + c) * total_num_points + p];
565               for (CeedInt d = 0; d < dim; d++) {
566                 // ------ Tensor contract with current Chebyshev polynomial values
567                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
568                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
569                 CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode,
570                                                  (p > 0 || (p == 0 && pass > 0)) && d == (dim - 1), tmp[d % 2],
571                                                  d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
572                 pre /= 1;
573                 post *= Q_1d;
574               }
575             }
576           }
577           break;
578         }
579         default:
580           // Nothing to do, excluded above
581           break;
582       }
583       CeedCall(CeedVectorRestoreArray(basis->vec_chebyshev, &chebyshev_coeffs));
584       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
585       CeedCall(CeedVectorRestoreArrayRead(u, &u_array));
586 
587       // -- Interpolate transpose from Chebyshev coefficients
588       if (apply_add) CeedCall(CeedBasisApplyAdd(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
589       else CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
590       break;
591     }
592   }
593   return CEED_ERROR_SUCCESS;
594 }
595 
596 /// @}
597 
598 /// ----------------------------------------------------------------------------
599 /// Ceed Backend API
600 /// ----------------------------------------------------------------------------
601 /// @addtogroup CeedBasisBackend
602 /// @{
603 
604 /**
605   @brief Return collocated gradient matrix
606 
607   @param[in]  basis         `CeedBasis`
608   @param[out] collo_grad_1d Row-major (`Q_1d * Q_1d`) matrix expressing derivatives of basis functions at quadrature points
609 
610   @return An error code: 0 - success, otherwise - failure
611 
612   @ref Backend
613 **/
614 int CeedBasisGetCollocatedGrad(CeedBasis basis, CeedScalar *collo_grad_1d) {
615   Ceed              ceed;
616   CeedInt           P_1d, Q_1d;
617   CeedScalar       *interp_1d_pinv;
618   const CeedScalar *grad_1d, *interp_1d;
619 
620   // Note: This function is for backend use, so all errors are terminal and we do not need to clean up memory on failure.
621   CeedCall(CeedBasisGetCeed(basis, &ceed));
622   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
623   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
624 
625   // Compute interp_1d^+, pseudoinverse of interp_1d
626   CeedCall(CeedCalloc(P_1d * Q_1d, &interp_1d_pinv));
627   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
628   CeedCall(CeedMatrixPseudoinverse(ceed, interp_1d, Q_1d, P_1d, interp_1d_pinv));
629   CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
630   CeedCall(CeedMatrixMatrixMultiply(ceed, grad_1d, (const CeedScalar *)interp_1d_pinv, collo_grad_1d, Q_1d, Q_1d, P_1d));
631 
632   CeedCall(CeedFree(&interp_1d_pinv));
633   return CEED_ERROR_SUCCESS;
634 }
635 
636 /**
637   @brief Return 1D interpolation matrix to Chebyshev polynomial coefficients on quadrature space
638 
639   @param[in]  basis               `CeedBasis`
640   @param[out] chebyshev_interp_1d Row-major (`P_1d * Q_1d`) matrix interpolating from basis nodes to Chebyshev polynomial coefficients
641 
642   @return An error code: 0 - success, otherwise - failure
643 
644   @ref Backend
645 **/
646 int CeedBasisGetChebyshevInterp1D(CeedBasis basis, CeedScalar *chebyshev_interp_1d) {
647   CeedInt           P_1d, Q_1d;
648   CeedScalar       *C, *chebyshev_coeffs_1d_inv;
649   const CeedScalar *interp_1d, *q_ref_1d;
650   Ceed              ceed;
651 
652   CeedCall(CeedBasisGetCeed(basis, &ceed));
653   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
654   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
655 
656   // Build coefficient matrix
657   // -- Note: Clang-tidy needs this check
658   CeedCheck((P_1d > 0) && (Q_1d > 0), ceed, CEED_ERROR_INCOMPATIBLE, "CeedBasis dimensions are malformed");
659   CeedCall(CeedCalloc(Q_1d * Q_1d, &C));
660   CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
661   for (CeedInt i = 0; i < Q_1d; i++) CeedCall(CeedChebyshevPolynomialsAtPoint(q_ref_1d[i], Q_1d, &C[i * Q_1d]));
662 
663   // Compute C^+, pseudoinverse of coefficient matrix
664   CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_coeffs_1d_inv));
665   CeedCall(CeedMatrixPseudoinverse(ceed, C, Q_1d, Q_1d, chebyshev_coeffs_1d_inv));
666 
667   // Build mapping from nodes to Chebyshev coefficients
668   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
669   CeedCall(CeedMatrixMatrixMultiply(ceed, chebyshev_coeffs_1d_inv, interp_1d, chebyshev_interp_1d, Q_1d, P_1d, Q_1d));
670 
671   // Cleanup
672   CeedCall(CeedFree(&C));
673   CeedCall(CeedFree(&chebyshev_coeffs_1d_inv));
674   return CEED_ERROR_SUCCESS;
675 }
676 
677 /**
678   @brief Get tensor status for given `CeedBasis`
679 
680   @param[in]  basis     `CeedBasis`
681   @param[out] is_tensor Variable to store tensor status
682 
683   @return An error code: 0 - success, otherwise - failure
684 
685   @ref Backend
686 **/
687 int CeedBasisIsTensor(CeedBasis basis, bool *is_tensor) {
688   *is_tensor = basis->is_tensor_basis;
689   return CEED_ERROR_SUCCESS;
690 }
691 
692 /**
693   @brief Get backend data of a `CeedBasis`
694 
695   @param[in]  basis `CeedBasis`
696   @param[out] data  Variable to store data
697 
698   @return An error code: 0 - success, otherwise - failure
699 
700   @ref Backend
701 **/
702 int CeedBasisGetData(CeedBasis basis, void *data) {
703   *(void **)data = basis->data;
704   return CEED_ERROR_SUCCESS;
705 }
706 
707 /**
708   @brief Set backend data of a `CeedBasis`
709 
710   @param[in,out] basis  `CeedBasis`
711   @param[in]     data   Data to set
712 
713   @return An error code: 0 - success, otherwise - failure
714 
715   @ref Backend
716 **/
717 int CeedBasisSetData(CeedBasis basis, void *data) {
718   basis->data = data;
719   return CEED_ERROR_SUCCESS;
720 }
721 
722 /**
723   @brief Increment the reference counter for a `CeedBasis`
724 
725   @param[in,out] basis `CeedBasis` to increment the reference counter
726 
727   @return An error code: 0 - success, otherwise - failure
728 
729   @ref Backend
730 **/
731 int CeedBasisReference(CeedBasis basis) {
732   basis->ref_count++;
733   return CEED_ERROR_SUCCESS;
734 }
735 
736 /**
737   @brief Get number of Q-vector components for given `CeedBasis`
738 
739   @param[in]  basis     `CeedBasis`
740   @param[in]  eval_mode @ref CEED_EVAL_INTERP to use interpolated values,
741                           @ref CEED_EVAL_GRAD to use gradients,
742                           @ref CEED_EVAL_DIV to use divergence,
743                           @ref CEED_EVAL_CURL to use curl
744   @param[out] q_comp    Variable to store number of Q-vector components of basis
745 
746   @return An error code: 0 - success, otherwise - failure
747 
748   @ref Backend
749 **/
750 int CeedBasisGetNumQuadratureComponents(CeedBasis basis, CeedEvalMode eval_mode, CeedInt *q_comp) {
751   CeedInt dim;
752 
753   CeedCall(CeedBasisGetDimension(basis, &dim));
754   switch (eval_mode) {
755     case CEED_EVAL_INTERP: {
756       CeedFESpace fe_space;
757 
758       CeedCall(CeedBasisGetFESpace(basis, &fe_space));
759       *q_comp = (fe_space == CEED_FE_SPACE_H1) ? 1 : dim;
760     } break;
761     case CEED_EVAL_GRAD:
762       *q_comp = dim;
763       break;
764     case CEED_EVAL_DIV:
765       *q_comp = 1;
766       break;
767     case CEED_EVAL_CURL:
768       *q_comp = (dim < 3) ? 1 : dim;
769       break;
770     case CEED_EVAL_NONE:
771     case CEED_EVAL_WEIGHT:
772       *q_comp = 1;
773       break;
774   }
775   return CEED_ERROR_SUCCESS;
776 }
777 
778 /**
779   @brief Estimate number of FLOPs required to apply `CeedBasis` in `t_mode` and `eval_mode`
780 
781   @param[in]  basis     `CeedBasis` to estimate FLOPs for
782   @param[in]  t_mode    Apply basis or transpose
783   @param[in]  eval_mode @ref CeedEvalMode
784   @param[out] flops     Address of variable to hold FLOPs estimate
785 
786   @ref Backend
787 **/
788 int CeedBasisGetFlopsEstimate(CeedBasis basis, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedSize *flops) {
789   bool is_tensor;
790 
791   CeedCall(CeedBasisIsTensor(basis, &is_tensor));
792   if (is_tensor) {
793     CeedInt dim, num_comp, P_1d, Q_1d;
794 
795     CeedCall(CeedBasisGetDimension(basis, &dim));
796     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
797     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
798     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
799     if (t_mode == CEED_TRANSPOSE) {
800       P_1d = Q_1d;
801       Q_1d = P_1d;
802     }
803     CeedInt tensor_flops = 0, pre = num_comp * CeedIntPow(P_1d, dim - 1), post = 1;
804     for (CeedInt d = 0; d < dim; d++) {
805       tensor_flops += 2 * pre * P_1d * post * Q_1d;
806       pre /= P_1d;
807       post *= Q_1d;
808     }
809     switch (eval_mode) {
810       case CEED_EVAL_NONE:
811         *flops = 0;
812         break;
813       case CEED_EVAL_INTERP:
814         *flops = tensor_flops;
815         break;
816       case CEED_EVAL_GRAD:
817         *flops = tensor_flops * 2;
818         break;
819       case CEED_EVAL_DIV:
820       case CEED_EVAL_CURL: {
821         // LCOV_EXCL_START
822         return CeedError(CeedBasisReturnCeed(basis), CEED_ERROR_INCOMPATIBLE, "Tensor basis evaluation for %s not supported",
823                          CeedEvalModes[eval_mode]);
824         break;
825         // LCOV_EXCL_STOP
826       }
827       case CEED_EVAL_WEIGHT:
828         *flops = dim * CeedIntPow(Q_1d, dim);
829         break;
830     }
831   } else {
832     CeedInt dim, num_comp, q_comp, num_nodes, num_qpts;
833 
834     CeedCall(CeedBasisGetDimension(basis, &dim));
835     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
836     CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
837     CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
838     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
839     switch (eval_mode) {
840       case CEED_EVAL_NONE:
841         *flops = 0;
842         break;
843       case CEED_EVAL_INTERP:
844       case CEED_EVAL_GRAD:
845       case CEED_EVAL_DIV:
846       case CEED_EVAL_CURL:
847         *flops = num_nodes * num_qpts * num_comp * q_comp;
848         break;
849       case CEED_EVAL_WEIGHT:
850         *flops = 0;
851         break;
852     }
853   }
854   return CEED_ERROR_SUCCESS;
855 }
856 
857 /**
858   @brief Get `CeedFESpace` for a `CeedBasis`
859 
860   @param[in]  basis    `CeedBasis`
861   @param[out] fe_space Variable to store `CeedFESpace`
862 
863   @return An error code: 0 - success, otherwise - failure
864 
865   @ref Backend
866 **/
867 int CeedBasisGetFESpace(CeedBasis basis, CeedFESpace *fe_space) {
868   *fe_space = basis->fe_space;
869   return CEED_ERROR_SUCCESS;
870 }
871 
872 /**
873   @brief Get dimension for given `CeedElemTopology`
874 
875   @param[in]  topo `CeedElemTopology`
876   @param[out] dim  Variable to store dimension of topology
877 
878   @return An error code: 0 - success, otherwise - failure
879 
880   @ref Backend
881 **/
882 int CeedBasisGetTopologyDimension(CeedElemTopology topo, CeedInt *dim) {
883   *dim = (CeedInt)topo >> 16;
884   return CEED_ERROR_SUCCESS;
885 }
886 
887 /**
888   @brief Get `CeedTensorContract` of a `CeedBasis`
889 
890   @param[in]  basis     `CeedBasis`
891   @param[out] contract  Variable to store `CeedTensorContract`
892 
893   @return An error code: 0 - success, otherwise - failure
894 
895   @ref Backend
896 **/
897 int CeedBasisGetTensorContract(CeedBasis basis, CeedTensorContract *contract) {
898   *contract = basis->contract;
899   return CEED_ERROR_SUCCESS;
900 }
901 
902 /**
903   @brief Set `CeedTensorContract` of a `CeedBasis`
904 
905   @param[in,out] basis    `CeedBasis`
906   @param[in]     contract `CeedTensorContract` to set
907 
908   @return An error code: 0 - success, otherwise - failure
909 
910   @ref Backend
911 **/
912 int CeedBasisSetTensorContract(CeedBasis basis, CeedTensorContract contract) {
913   basis->contract = contract;
914   CeedCall(CeedTensorContractReference(contract));
915   return CEED_ERROR_SUCCESS;
916 }
917 
918 /**
919   @brief Return a reference implementation of matrix multiplication \f$C = A B\f$.
920 
921   Note: This is a reference implementation for CPU `CeedScalar` pointers that is not intended for high performance.
922 
923   @param[in]  ceed  `Ceed` context for error handling
924   @param[in]  mat_A Row-major matrix `A`
925   @param[in]  mat_B Row-major matrix `B`
926   @param[out] mat_C Row-major output matrix `C`
927   @param[in]  m     Number of rows of `C`
928   @param[in]  n     Number of columns of `C`
929   @param[in]  kk    Number of columns of `A`/rows of `B`
930 
931   @return An error code: 0 - success, otherwise - failure
932 
933   @ref Utility
934 **/
935 int CeedMatrixMatrixMultiply(Ceed ceed, const CeedScalar *mat_A, const CeedScalar *mat_B, CeedScalar *mat_C, CeedInt m, CeedInt n, CeedInt kk) {
936   for (CeedInt i = 0; i < m; i++) {
937     for (CeedInt j = 0; j < n; j++) {
938       CeedScalar sum = 0;
939 
940       for (CeedInt k = 0; k < kk; k++) sum += mat_A[k + i * kk] * mat_B[j + k * n];
941       mat_C[j + i * n] = sum;
942     }
943   }
944   return CEED_ERROR_SUCCESS;
945 }
946 
947 /**
948   @brief Return QR Factorization of a matrix
949 
950   @param[in]     ceed `Ceed` context for error handling
951   @param[in,out] mat  Row-major matrix to be factorized in place
952   @param[in,out] tau  Vector of length `m` of scaling factors
953   @param[in]     m    Number of rows
954   @param[in]     n    Number of columns
955 
956   @return An error code: 0 - success, otherwise - failure
957 
958   @ref Utility
959 **/
960 int CeedQRFactorization(Ceed ceed, CeedScalar *mat, CeedScalar *tau, CeedInt m, CeedInt n) {
961   CeedScalar v[m];
962 
963   // Check matrix shape
964   CeedCheck(n <= m, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute QR factorization with n > m");
965 
966   for (CeedInt i = 0; i < n; i++) {
967     CeedScalar sigma = 0.0;
968 
969     if (i >= m - 1) {  // last row of matrix, no reflection needed
970       tau[i] = 0.;
971       break;
972     }
973     // Calculate Householder vector, magnitude
974     v[i] = mat[i + n * i];
975     for (CeedInt j = i + 1; j < m; j++) {
976       v[j] = mat[i + n * j];
977       sigma += v[j] * v[j];
978     }
979     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:m]
980     const CeedScalar R_ii = -copysign(norm, v[i]);
981 
982     v[i] -= R_ii;
983     // norm of v[i:m] after modification above and scaling below
984     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
985     //   tau = 2 / (norm*norm)
986     tau[i] = 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
987     for (CeedInt j = i + 1; j < m; j++) v[j] /= v[i];
988 
989     // Apply Householder reflector to lower right panel
990     CeedHouseholderReflect(&mat[i * n + i + 1], &v[i], tau[i], m - i, n - i - 1, n, 1);
991     // Save v
992     mat[i + n * i] = R_ii;
993     for (CeedInt j = i + 1; j < m; j++) mat[i + n * j] = v[j];
994   }
995   return CEED_ERROR_SUCCESS;
996 }
997 
998 /**
999   @brief Apply Householder Q matrix
1000 
1001   Compute `mat_A = mat_Q mat_A`, where `mat_Q` is \f$m \times m\f$ and `mat_A` is \f$m \times n\f$.
1002 
1003   @param[in,out] mat_A  Matrix to apply Householder Q to, in place
1004   @param[in]     mat_Q  Householder Q matrix
1005   @param[in]     tau    Householder scaling factors
1006   @param[in]     t_mode Transpose mode for application
1007   @param[in]     m      Number of rows in `A`
1008   @param[in]     n      Number of columns in `A`
1009   @param[in]     k      Number of elementary reflectors in Q, `k < m`
1010   @param[in]     row    Row stride in `A`
1011   @param[in]     col    Col stride in `A`
1012 
1013   @return An error code: 0 - success, otherwise - failure
1014 
1015   @ref Utility
1016 **/
1017 int CeedHouseholderApplyQ(CeedScalar *mat_A, const CeedScalar *mat_Q, const CeedScalar *tau, CeedTransposeMode t_mode, CeedInt m, CeedInt n,
1018                           CeedInt k, CeedInt row, CeedInt col) {
1019   CeedScalar *v;
1020 
1021   CeedCall(CeedMalloc(m, &v));
1022   for (CeedInt ii = 0; ii < k; ii++) {
1023     CeedInt i = t_mode == CEED_TRANSPOSE ? ii : k - 1 - ii;
1024     for (CeedInt j = i + 1; j < m; j++) v[j] = mat_Q[j * k + i];
1025     // Apply Householder reflector (I - tau v v^T) collo_grad_1d^T
1026     CeedCall(CeedHouseholderReflect(&mat_A[i * row], &v[i], tau[i], m - i, n, row, col));
1027   }
1028   CeedCall(CeedFree(&v));
1029   return CEED_ERROR_SUCCESS;
1030 }
1031 
1032 /**
1033   @brief Return pseudoinverse of a matrix
1034 
1035   @param[in]     ceed      Ceed context for error handling
1036   @param[in]     mat       Row-major matrix to compute pseudoinverse of
1037   @param[in]     m         Number of rows
1038   @param[in]     n         Number of columns
1039   @param[out]    mat_pinv  Row-major pseudoinverse matrix
1040 
1041   @return An error code: 0 - success, otherwise - failure
1042 
1043   @ref Utility
1044 **/
1045 int CeedMatrixPseudoinverse(Ceed ceed, const CeedScalar *mat, CeedInt m, CeedInt n, CeedScalar *mat_pinv) {
1046   CeedScalar *tau, *I, *mat_copy;
1047 
1048   CeedCall(CeedCalloc(m, &tau));
1049   CeedCall(CeedCalloc(m * m, &I));
1050   CeedCall(CeedCalloc(m * n, &mat_copy));
1051   memcpy(mat_copy, mat, m * n * sizeof mat[0]);
1052 
1053   // QR Factorization, mat = Q R
1054   CeedCall(CeedQRFactorization(ceed, mat_copy, tau, m, n));
1055 
1056   // -- Apply Q^T, I = Q^T * I
1057   for (CeedInt i = 0; i < m; i++) I[i * m + i] = 1.0;
1058   CeedCall(CeedHouseholderApplyQ(I, mat_copy, tau, CEED_TRANSPOSE, m, m, n, m, 1));
1059   // -- Apply R_inv, mat_pinv = R_inv * Q^T
1060   for (CeedInt j = 0; j < m; j++) {  // Column j
1061     mat_pinv[j + m * (n - 1)] = I[j + m * (n - 1)] / mat_copy[n * n - 1];
1062     for (CeedInt i = n - 2; i >= 0; i--) {  // Row i
1063       mat_pinv[j + m * i] = I[j + m * i];
1064       for (CeedInt k = i + 1; k < n; k++) mat_pinv[j + m * i] -= mat_copy[k + n * i] * mat_pinv[j + m * k];
1065       mat_pinv[j + m * i] /= mat_copy[i + n * i];
1066     }
1067   }
1068 
1069   // Cleanup
1070   CeedCall(CeedFree(&I));
1071   CeedCall(CeedFree(&tau));
1072   CeedCall(CeedFree(&mat_copy));
1073   return CEED_ERROR_SUCCESS;
1074 }
1075 
1076 /**
1077   @brief Return symmetric Schur decomposition of the symmetric matrix mat via symmetric QR factorization
1078 
1079   @param[in]     ceed   `Ceed` context for error handling
1080   @param[in,out] mat    Row-major matrix to be factorized in place
1081   @param[out]    lambda Vector of length n of eigenvalues
1082   @param[in]     n      Number of rows/columns
1083 
1084   @return An error code: 0 - success, otherwise - failure
1085 
1086   @ref Utility
1087 **/
1088 CeedPragmaOptimizeOff
1089 int CeedSymmetricSchurDecomposition(Ceed ceed, CeedScalar *mat, CeedScalar *lambda, CeedInt n) {
1090   // Check bounds for clang-tidy
1091   CeedCheck(n > 1, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute symmetric Schur decomposition of scalars");
1092 
1093   CeedScalar v[n - 1], tau[n - 1], mat_T[n * n];
1094 
1095   // Copy mat to mat_T and set mat to I
1096   memcpy(mat_T, mat, n * n * sizeof(mat[0]));
1097   for (CeedInt i = 0; i < n; i++) {
1098     for (CeedInt j = 0; j < n; j++) mat[j + n * i] = (i == j) ? 1 : 0;
1099   }
1100 
1101   // Reduce to tridiagonal
1102   for (CeedInt i = 0; i < n - 1; i++) {
1103     // Calculate Householder vector, magnitude
1104     CeedScalar sigma = 0.0;
1105 
1106     v[i] = mat_T[i + n * (i + 1)];
1107     for (CeedInt j = i + 1; j < n - 1; j++) {
1108       v[j] = mat_T[i + n * (j + 1)];
1109       sigma += v[j] * v[j];
1110     }
1111     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:n-1]
1112     const CeedScalar R_ii = -copysign(norm, v[i]);
1113 
1114     v[i] -= R_ii;
1115     // norm of v[i:m] after modification above and scaling below
1116     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
1117     //   tau = 2 / (norm*norm)
1118     tau[i] = i == n - 2 ? 2 : 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
1119     for (CeedInt j = i + 1; j < n - 1; j++) v[j] /= v[i];
1120 
1121     // Update sub and super diagonal
1122     for (CeedInt j = i + 2; j < n; j++) {
1123       mat_T[i + n * j] = 0;
1124       mat_T[j + n * i] = 0;
1125     }
1126     // Apply symmetric Householder reflector to lower right panel
1127     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1128     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), 1, n);
1129 
1130     // Save v
1131     mat_T[i + n * (i + 1)] = R_ii;
1132     mat_T[(i + 1) + n * i] = R_ii;
1133     for (CeedInt j = i + 1; j < n - 1; j++) {
1134       mat_T[i + n * (j + 1)] = v[j];
1135     }
1136   }
1137   // Backwards accumulation of Q
1138   for (CeedInt i = n - 2; i >= 0; i--) {
1139     if (tau[i] > 0.0) {
1140       v[i] = 1;
1141       for (CeedInt j = i + 1; j < n - 1; j++) {
1142         v[j]                   = mat_T[i + n * (j + 1)];
1143         mat_T[i + n * (j + 1)] = 0;
1144       }
1145       CeedHouseholderReflect(&mat[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1146     }
1147   }
1148 
1149   // Reduce sub and super diagonal
1150   CeedInt    p = 0, q = 0, itr = 0, max_itr = n * n * n * n;
1151   CeedScalar tol = CEED_EPSILON;
1152 
1153   while (itr < max_itr) {
1154     // Update p, q, size of reduced portions of diagonal
1155     p = 0;
1156     q = 0;
1157     for (CeedInt i = n - 2; i >= 0; i--) {
1158       if (fabs(mat_T[i + n * (i + 1)]) < tol) q += 1;
1159       else break;
1160     }
1161     for (CeedInt i = 0; i < n - q - 1; i++) {
1162       if (fabs(mat_T[i + n * (i + 1)]) < tol) p += 1;
1163       else break;
1164     }
1165     if (q == n - 1) break;  // Finished reducing
1166 
1167     // Reduce tridiagonal portion
1168     CeedScalar t_nn = mat_T[(n - 1 - q) + n * (n - 1 - q)], t_nnm1 = mat_T[(n - 2 - q) + n * (n - 1 - q)];
1169     CeedScalar d  = (mat_T[(n - 2 - q) + n * (n - 2 - q)] - t_nn) / 2;
1170     CeedScalar mu = t_nn - t_nnm1 * t_nnm1 / (d + copysign(sqrt(d * d + t_nnm1 * t_nnm1), d));
1171     CeedScalar x  = mat_T[p + n * p] - mu;
1172     CeedScalar z  = mat_T[p + n * (p + 1)];
1173 
1174     for (CeedInt k = p; k < n - q - 1; k++) {
1175       // Compute Givens rotation
1176       CeedScalar c = 1, s = 0;
1177 
1178       if (fabs(z) > tol) {
1179         if (fabs(z) > fabs(x)) {
1180           const CeedScalar tau = -x / z;
1181 
1182           s = 1 / sqrt(1 + tau * tau);
1183           c = s * tau;
1184         } else {
1185           const CeedScalar tau = -z / x;
1186 
1187           c = 1 / sqrt(1 + tau * tau);
1188           s = c * tau;
1189         }
1190       }
1191 
1192       // Apply Givens rotation to T
1193       CeedGivensRotation(mat_T, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1194       CeedGivensRotation(mat_T, c, s, CEED_TRANSPOSE, k, k + 1, n, n);
1195 
1196       // Apply Givens rotation to Q
1197       CeedGivensRotation(mat, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1198 
1199       // Update x, z
1200       if (k < n - q - 2) {
1201         x = mat_T[k + n * (k + 1)];
1202         z = mat_T[k + n * (k + 2)];
1203       }
1204     }
1205     itr++;
1206   }
1207 
1208   // Save eigenvalues
1209   for (CeedInt i = 0; i < n; i++) lambda[i] = mat_T[i + n * i];
1210 
1211   // Check convergence
1212   CeedCheck(itr < max_itr || q > n, ceed, CEED_ERROR_MINOR, "Symmetric QR failed to converge");
1213   return CEED_ERROR_SUCCESS;
1214 }
1215 CeedPragmaOptimizeOn
1216 
1217 /**
1218   @brief Return Simultaneous Diagonalization of two matrices.
1219 
1220   This solves the generalized eigenvalue problem `A x = lambda B x`, where `A` and `B` are symmetric and `B` is positive definite.
1221   We generate the matrix `X` and vector `Lambda` such that `X^T A X = Lambda` and `X^T B X = I`.
1222   This is equivalent to the LAPACK routine 'sygv' with `TYPE = 1`.
1223 
1224   @param[in]  ceed   `Ceed` context for error handling
1225   @param[in]  mat_A  Row-major matrix to be factorized with eigenvalues
1226   @param[in]  mat_B  Row-major matrix to be factorized to identity
1227   @param[out] mat_X  Row-major orthogonal matrix
1228   @param[out] lambda Vector of length `n` of generalized eigenvalues
1229   @param[in]  n      Number of rows/columns
1230 
1231   @return An error code: 0 - success, otherwise - failure
1232 
1233   @ref Utility
1234 **/
1235 CeedPragmaOptimizeOff
1236 int CeedSimultaneousDiagonalization(Ceed ceed, CeedScalar *mat_A, CeedScalar *mat_B, CeedScalar *mat_X, CeedScalar *lambda, CeedInt n) {
1237   CeedScalar *mat_C, *mat_G, *vec_D;
1238 
1239   CeedCall(CeedCalloc(n * n, &mat_C));
1240   CeedCall(CeedCalloc(n * n, &mat_G));
1241   CeedCall(CeedCalloc(n, &vec_D));
1242 
1243   // Compute B = G D G^T
1244   memcpy(mat_G, mat_B, n * n * sizeof(mat_B[0]));
1245   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_G, vec_D, n));
1246 
1247   // Sort eigenvalues
1248   for (CeedInt i = n - 1; i >= 0; i--) {
1249     for (CeedInt j = 0; j < i; j++) {
1250       if (fabs(vec_D[j]) > fabs(vec_D[j + 1])) {
1251         CeedScalarSwap(vec_D[j], vec_D[j + 1]);
1252         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_G[k * n + j], mat_G[k * n + j + 1]);
1253       }
1254     }
1255   }
1256 
1257   // Compute C = (G D^1/2)^-1 A (G D^1/2)^-T
1258   //           = D^-1/2 G^T A G D^-1/2
1259   // -- D = D^-1/2
1260   for (CeedInt i = 0; i < n; i++) vec_D[i] = 1. / sqrt(vec_D[i]);
1261   // -- G = G D^-1/2
1262   // -- C = D^-1/2 G^T
1263   for (CeedInt i = 0; i < n; i++) {
1264     for (CeedInt j = 0; j < n; j++) {
1265       mat_G[i * n + j] *= vec_D[j];
1266       mat_C[j * n + i] = mat_G[i * n + j];
1267     }
1268   }
1269   // -- X = (D^-1/2 G^T) A
1270   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_C, (const CeedScalar *)mat_A, mat_X, n, n, n));
1271   // -- C = (D^-1/2 G^T A) (G D^-1/2)
1272   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_X, (const CeedScalar *)mat_G, mat_C, n, n, n));
1273 
1274   // Compute Q^T C Q = lambda
1275   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_C, lambda, n));
1276 
1277   // Sort eigenvalues
1278   for (CeedInt i = n - 1; i >= 0; i--) {
1279     for (CeedInt j = 0; j < i; j++) {
1280       if (fabs(lambda[j]) > fabs(lambda[j + 1])) {
1281         CeedScalarSwap(lambda[j], lambda[j + 1]);
1282         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_C[k * n + j], mat_C[k * n + j + 1]);
1283       }
1284     }
1285   }
1286 
1287   // Set X = (G D^1/2)^-T Q
1288   //       = G D^-1/2 Q
1289   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_G, (const CeedScalar *)mat_C, mat_X, n, n, n));
1290 
1291   // Cleanup
1292   CeedCall(CeedFree(&mat_C));
1293   CeedCall(CeedFree(&mat_G));
1294   CeedCall(CeedFree(&vec_D));
1295   return CEED_ERROR_SUCCESS;
1296 }
1297 CeedPragmaOptimizeOn
1298 
1299 /// @}
1300 
1301 /// ----------------------------------------------------------------------------
1302 /// CeedBasis Public API
1303 /// ----------------------------------------------------------------------------
1304 /// @addtogroup CeedBasisUser
1305 /// @{
1306 
1307 /**
1308   @brief Create a tensor-product basis for \f$H^1\f$ discretizations
1309 
1310   @param[in]  ceed        `Ceed` object used to create the `CeedBasis`
1311   @param[in]  dim         Topological dimension
1312   @param[in]  num_comp    Number of field components (1 for scalar fields)
1313   @param[in]  P_1d        Number of nodes in one dimension
1314   @param[in]  Q_1d        Number of quadrature points in one dimension
1315   @param[in]  interp_1d   Row-major (`Q_1d * P_1d`) matrix expressing the values of nodal basis functions at quadrature points
1316   @param[in]  grad_1d     Row-major (`Q_1d * P_1d`) matrix expressing derivatives of nodal basis functions at quadrature points
1317   @param[in]  q_ref_1d    Array of length `Q_1d` holding the locations of quadrature points on the 1D reference element `[-1, 1]`
1318   @param[in]  q_weight_1d Array of length `Q_1d` holding the quadrature weights on the reference element
1319   @param[out] basis       Address of the variable where the newly created `CeedBasis` will be stored
1320 
1321   @return An error code: 0 - success, otherwise - failure
1322 
1323   @ref User
1324 **/
1325 int CeedBasisCreateTensorH1(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P_1d, CeedInt Q_1d, const CeedScalar *interp_1d,
1326                             const CeedScalar *grad_1d, const CeedScalar *q_ref_1d, const CeedScalar *q_weight_1d, CeedBasis *basis) {
1327   if (!ceed->BasisCreateTensorH1) {
1328     Ceed delegate;
1329 
1330     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1331     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateTensorH1");
1332     CeedCall(CeedBasisCreateTensorH1(delegate, dim, num_comp, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1333     return CEED_ERROR_SUCCESS;
1334   }
1335 
1336   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1337   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1338   CeedCheck(P_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1339   CeedCheck(Q_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1340 
1341   CeedElemTopology topo = dim == 1 ? CEED_TOPOLOGY_LINE : dim == 2 ? CEED_TOPOLOGY_QUAD : CEED_TOPOLOGY_HEX;
1342 
1343   CeedCall(CeedCalloc(1, basis));
1344   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1345   (*basis)->ref_count       = 1;
1346   (*basis)->is_tensor_basis = true;
1347   (*basis)->dim             = dim;
1348   (*basis)->topo            = topo;
1349   (*basis)->num_comp        = num_comp;
1350   (*basis)->P_1d            = P_1d;
1351   (*basis)->Q_1d            = Q_1d;
1352   (*basis)->P               = CeedIntPow(P_1d, dim);
1353   (*basis)->Q               = CeedIntPow(Q_1d, dim);
1354   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1355   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_ref_1d));
1356   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_weight_1d));
1357   if (q_ref_1d) memcpy((*basis)->q_ref_1d, q_ref_1d, Q_1d * sizeof(q_ref_1d[0]));
1358   if (q_weight_1d) memcpy((*basis)->q_weight_1d, q_weight_1d, Q_1d * sizeof(q_weight_1d[0]));
1359   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->interp_1d));
1360   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->grad_1d));
1361   if (interp_1d) memcpy((*basis)->interp_1d, interp_1d, Q_1d * P_1d * sizeof(interp_1d[0]));
1362   if (grad_1d) memcpy((*basis)->grad_1d, grad_1d, Q_1d * P_1d * sizeof(grad_1d[0]));
1363   CeedCall(ceed->BasisCreateTensorH1(dim, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, *basis));
1364   return CEED_ERROR_SUCCESS;
1365 }
1366 
1367 /**
1368   @brief Create a tensor-product \f$H^1\f$ Lagrange basis
1369 
1370   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1371   @param[in]  dim       Topological dimension of element
1372   @param[in]  num_comp  Number of field components (1 for scalar fields)
1373   @param[in]  P         Number of Gauss-Lobatto nodes in one dimension.
1374                           The polynomial degree of the resulting `Q_k` element is `k = P - 1`.
1375   @param[in]  Q         Number of quadrature points in one dimension.
1376   @param[in]  quad_mode Distribution of the `Q` quadrature points (affects order of accuracy for the quadrature)
1377   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1378 
1379   @return An error code: 0 - success, otherwise - failure
1380 
1381   @ref User
1382 **/
1383 int CeedBasisCreateTensorH1Lagrange(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P, CeedInt Q, CeedQuadMode quad_mode, CeedBasis *basis) {
1384   // Allocate
1385   int        ierr = CEED_ERROR_SUCCESS;
1386   CeedScalar c1, c2, c3, c4, dx, *nodes, *interp_1d, *grad_1d, *q_ref_1d, *q_weight_1d;
1387 
1388   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1389   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1390   CeedCheck(P > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1391   CeedCheck(Q > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1392 
1393   // Get Nodes and Weights
1394   CeedCall(CeedCalloc(P * Q, &interp_1d));
1395   CeedCall(CeedCalloc(P * Q, &grad_1d));
1396   CeedCall(CeedCalloc(P, &nodes));
1397   CeedCall(CeedCalloc(Q, &q_ref_1d));
1398   CeedCall(CeedCalloc(Q, &q_weight_1d));
1399   if (CeedLobattoQuadrature(P, nodes, NULL) != CEED_ERROR_SUCCESS) goto cleanup;
1400   switch (quad_mode) {
1401     case CEED_GAUSS:
1402       ierr = CeedGaussQuadrature(Q, q_ref_1d, q_weight_1d);
1403       break;
1404     case CEED_GAUSS_LOBATTO:
1405       ierr = CeedLobattoQuadrature(Q, q_ref_1d, q_weight_1d);
1406       break;
1407   }
1408   if (ierr != CEED_ERROR_SUCCESS) goto cleanup;
1409 
1410   // Build B, D matrix
1411   // Fornberg, 1998
1412   for (CeedInt i = 0; i < Q; i++) {
1413     c1                   = 1.0;
1414     c3                   = nodes[0] - q_ref_1d[i];
1415     interp_1d[i * P + 0] = 1.0;
1416     for (CeedInt j = 1; j < P; j++) {
1417       c2 = 1.0;
1418       c4 = c3;
1419       c3 = nodes[j] - q_ref_1d[i];
1420       for (CeedInt k = 0; k < j; k++) {
1421         dx = nodes[j] - nodes[k];
1422         c2 *= dx;
1423         if (k == j - 1) {
1424           grad_1d[i * P + j]   = c1 * (interp_1d[i * P + k] - c4 * grad_1d[i * P + k]) / c2;
1425           interp_1d[i * P + j] = -c1 * c4 * interp_1d[i * P + k] / c2;
1426         }
1427         grad_1d[i * P + k]   = (c3 * grad_1d[i * P + k] - interp_1d[i * P + k]) / dx;
1428         interp_1d[i * P + k] = c3 * interp_1d[i * P + k] / dx;
1429       }
1430       c1 = c2;
1431     }
1432   }
1433   // Pass to CeedBasisCreateTensorH1
1434   CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P, Q, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1435 cleanup:
1436   CeedCall(CeedFree(&interp_1d));
1437   CeedCall(CeedFree(&grad_1d));
1438   CeedCall(CeedFree(&nodes));
1439   CeedCall(CeedFree(&q_ref_1d));
1440   CeedCall(CeedFree(&q_weight_1d));
1441   return CEED_ERROR_SUCCESS;
1442 }
1443 
1444 /**
1445   @brief Create a non tensor-product basis for \f$H^1\f$ discretizations
1446 
1447   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1448   @param[in]  topo      Topology of element, e.g. hypercube, simplex, etc
1449   @param[in]  num_comp  Number of field components (1 for scalar fields)
1450   @param[in]  num_nodes Total number of nodes
1451   @param[in]  num_qpts  Total number of quadrature points
1452   @param[in]  interp    Row-major (`num_qpts * num_nodes`) matrix expressing the values of nodal basis functions at quadrature points
1453   @param[in]  grad      Row-major (`dim * num_qpts * num_nodes`) matrix expressing derivatives of nodal basis functions at quadrature points
1454   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1455   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1456   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1457 
1458   @return An error code: 0 - success, otherwise - failure
1459 
1460   @ref User
1461 **/
1462 int CeedBasisCreateH1(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1463                       const CeedScalar *grad, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1464   CeedInt P = num_nodes, Q = num_qpts, dim = 0;
1465 
1466   if (!ceed->BasisCreateH1) {
1467     Ceed delegate;
1468 
1469     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1470     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateH1");
1471     CeedCall(CeedBasisCreateH1(delegate, topo, num_comp, num_nodes, num_qpts, interp, grad, q_ref, q_weight, basis));
1472     return CEED_ERROR_SUCCESS;
1473   }
1474 
1475   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1476   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1477   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1478 
1479   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1480 
1481   CeedCall(CeedCalloc(1, basis));
1482   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1483   (*basis)->ref_count       = 1;
1484   (*basis)->is_tensor_basis = false;
1485   (*basis)->dim             = dim;
1486   (*basis)->topo            = topo;
1487   (*basis)->num_comp        = num_comp;
1488   (*basis)->P               = P;
1489   (*basis)->Q               = Q;
1490   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1491   CeedCall(CeedCalloc(Q * dim, &(*basis)->q_ref_1d));
1492   CeedCall(CeedCalloc(Q, &(*basis)->q_weight_1d));
1493   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1494   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1495   CeedCall(CeedCalloc(Q * P, &(*basis)->interp));
1496   CeedCall(CeedCalloc(dim * Q * P, &(*basis)->grad));
1497   if (interp) memcpy((*basis)->interp, interp, Q * P * sizeof(interp[0]));
1498   if (grad) memcpy((*basis)->grad, grad, dim * Q * P * sizeof(grad[0]));
1499   CeedCall(ceed->BasisCreateH1(topo, dim, P, Q, interp, grad, q_ref, q_weight, *basis));
1500   return CEED_ERROR_SUCCESS;
1501 }
1502 
1503 /**
1504   @brief Create a non tensor-product basis for \f$H(\mathrm{div})\f$ discretizations
1505 
1506   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1507   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1508   @param[in]  num_comp  Number of components (usually 1 for vectors in H(div) bases)
1509   @param[in]  num_nodes Total number of nodes (DoFs per element)
1510   @param[in]  num_qpts  Total number of quadrature points
1511   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1512   @param[in]  div       Row-major (`num_qpts * num_nodes`) matrix expressing divergence of basis functions at quadrature points
1513   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1514   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1515   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1516 
1517   @return An error code: 0 - success, otherwise - failure
1518 
1519   @ref User
1520 **/
1521 int CeedBasisCreateHdiv(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1522                         const CeedScalar *div, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1523   CeedInt Q = num_qpts, P = num_nodes, dim = 0;
1524 
1525   if (!ceed->BasisCreateHdiv) {
1526     Ceed delegate;
1527 
1528     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1529     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHdiv");
1530     CeedCall(CeedBasisCreateHdiv(delegate, topo, num_comp, num_nodes, num_qpts, interp, div, q_ref, q_weight, basis));
1531     return CEED_ERROR_SUCCESS;
1532   }
1533 
1534   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1535   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1536   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1537 
1538   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1539 
1540   CeedCall(CeedCalloc(1, basis));
1541   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1542   (*basis)->ref_count       = 1;
1543   (*basis)->is_tensor_basis = false;
1544   (*basis)->dim             = dim;
1545   (*basis)->topo            = topo;
1546   (*basis)->num_comp        = num_comp;
1547   (*basis)->P               = P;
1548   (*basis)->Q               = Q;
1549   (*basis)->fe_space        = CEED_FE_SPACE_HDIV;
1550   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1551   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1552   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1553   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1554   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1555   CeedCall(CeedMalloc(Q * P, &(*basis)->div));
1556   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1557   if (div) memcpy((*basis)->div, div, Q * P * sizeof(div[0]));
1558   CeedCall(ceed->BasisCreateHdiv(topo, dim, P, Q, interp, div, q_ref, q_weight, *basis));
1559   return CEED_ERROR_SUCCESS;
1560 }
1561 
1562 /**
1563   @brief Create a non tensor-product basis for \f$H(\mathrm{curl})\f$ discretizations
1564 
1565   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1566   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1567   @param[in]  num_comp  Number of components (usually 1 for vectors in \f$H(\mathrm{curl})\f$ bases)
1568   @param[in]  num_nodes Total number of nodes (DoFs per element)
1569   @param[in]  num_qpts  Total number of quadrature points
1570   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1571   @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
1572   @param[in]  q_ref     Array of length `num_qpts * dim` holding the locations of quadrature points on the reference element
1573   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1574   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1575 
1576   @return An error code: 0 - success, otherwise - failure
1577 
1578   @ref User
1579 **/
1580 int CeedBasisCreateHcurl(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1581                          const CeedScalar *curl, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1582   CeedInt Q = num_qpts, P = num_nodes, dim = 0, curl_comp = 0;
1583 
1584   if (!ceed->BasisCreateHcurl) {
1585     Ceed delegate;
1586 
1587     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1588     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHcurl");
1589     CeedCall(CeedBasisCreateHcurl(delegate, topo, num_comp, num_nodes, num_qpts, interp, curl, q_ref, q_weight, basis));
1590     return CEED_ERROR_SUCCESS;
1591   }
1592 
1593   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1594   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1595   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1596 
1597   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1598   curl_comp = (dim < 3) ? 1 : dim;
1599 
1600   CeedCall(CeedCalloc(1, basis));
1601   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1602   (*basis)->ref_count       = 1;
1603   (*basis)->is_tensor_basis = false;
1604   (*basis)->dim             = dim;
1605   (*basis)->topo            = topo;
1606   (*basis)->num_comp        = num_comp;
1607   (*basis)->P               = P;
1608   (*basis)->Q               = Q;
1609   (*basis)->fe_space        = CEED_FE_SPACE_HCURL;
1610   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1611   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1612   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1613   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1614   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1615   CeedCall(CeedMalloc(curl_comp * Q * P, &(*basis)->curl));
1616   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1617   if (curl) memcpy((*basis)->curl, curl, curl_comp * Q * P * sizeof(curl[0]));
1618   CeedCall(ceed->BasisCreateHcurl(topo, dim, P, Q, interp, curl, q_ref, q_weight, *basis));
1619   return CEED_ERROR_SUCCESS;
1620 }
1621 
1622 /**
1623   @brief Create a `CeedBasis` for projection from the nodes of `basis_from` to the nodes of `basis_to`.
1624 
1625   Only @ref CEED_EVAL_INTERP will be valid for the new basis, `basis_project`.
1626   For \f$H^1\f$ spaces, @ref CEED_EVAL_GRAD will also be valid.
1627   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
1628   The gradient (for the \f$H^1\f$ case) is given by `grad_project = interp_to^+ * grad_from`.
1629 
1630   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
1631 
1632   Note: `basis_project` will have the same number of components as `basis_from`, regardless of the number of components that `basis_to` has.
1633         If `basis_from` has 3 components and `basis_to` has 5 components, then `basis_project` will have 3 components.
1634 
1635   Note: If either `basis_from` or `basis_to` are non-tensor, then `basis_project` will also be non-tensor
1636 
1637   @param[in]  basis_from    `CeedBasis` to prolong from
1638   @param[in]  basis_to      `CeedBasis` to prolong to
1639   @param[out] basis_project 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 CeedBasisCreateProjection(CeedBasis basis_from, CeedBasis basis_to, CeedBasis *basis_project) {
1646   Ceed        ceed;
1647   bool        create_tensor;
1648   CeedInt     dim, num_comp;
1649   CeedScalar *interp_project, *grad_project;
1650 
1651   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
1652 
1653   // Create projection matrix
1654   CeedCall(CeedBasisCreateProjectionMatrices(basis_from, basis_to, &interp_project, &grad_project));
1655 
1656   // Build basis
1657   {
1658     bool is_tensor_to, is_tensor_from;
1659 
1660     CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
1661     CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
1662     create_tensor = is_tensor_from && is_tensor_to;
1663   }
1664   CeedCall(CeedBasisGetDimension(basis_to, &dim));
1665   CeedCall(CeedBasisGetNumComponents(basis_from, &num_comp));
1666   if (create_tensor) {
1667     CeedInt P_1d_to, P_1d_from;
1668 
1669     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_1d_from));
1670     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_1d_to));
1671     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d_from, P_1d_to, interp_project, grad_project, NULL, NULL, basis_project));
1672   } else {
1673     // Even if basis_to and basis_from are not H1, the resulting basis is H1 for interpolation to work
1674     CeedInt          num_nodes_to, num_nodes_from;
1675     CeedElemTopology topo;
1676 
1677     CeedCall(CeedBasisGetTopology(basis_from, &topo));
1678     CeedCall(CeedBasisGetNumNodes(basis_from, &num_nodes_from));
1679     CeedCall(CeedBasisGetNumNodes(basis_to, &num_nodes_to));
1680     CeedCall(CeedBasisCreateH1(ceed, topo, num_comp, num_nodes_from, num_nodes_to, interp_project, grad_project, NULL, NULL, basis_project));
1681   }
1682 
1683   // Cleanup
1684   CeedCall(CeedFree(&interp_project));
1685   CeedCall(CeedFree(&grad_project));
1686   return CEED_ERROR_SUCCESS;
1687 }
1688 
1689 /**
1690   @brief Copy the pointer to a `CeedBasis`.
1691 
1692   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`.
1693         This `CeedBasis` will be destroyed if `*basis_copy` is the only reference to this `CeedBasis`.
1694 
1695   @param[in]     basis      `CeedBasis` to copy reference to
1696   @param[in,out] basis_copy Variable to store copied reference
1697 
1698   @return An error code: 0 - success, otherwise - failure
1699 
1700   @ref User
1701 **/
1702 int CeedBasisReferenceCopy(CeedBasis basis, CeedBasis *basis_copy) {
1703   if (basis != CEED_BASIS_NONE) CeedCall(CeedBasisReference(basis));
1704   CeedCall(CeedBasisDestroy(basis_copy));
1705   *basis_copy = basis;
1706   return CEED_ERROR_SUCCESS;
1707 }
1708 
1709 /**
1710   @brief View a `CeedBasis`
1711 
1712   @param[in] basis  `CeedBasis` to view
1713   @param[in] stream Stream to view to, e.g., `stdout`
1714 
1715   @return An error code: 0 - success, otherwise - failure
1716 
1717   @ref User
1718 **/
1719 int CeedBasisView(CeedBasis basis, FILE *stream) {
1720   bool             is_tensor_basis;
1721   CeedElemTopology topo;
1722   CeedFESpace      fe_space;
1723 
1724   // Basis data
1725   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
1726   CeedCall(CeedBasisGetTopology(basis, &topo));
1727   CeedCall(CeedBasisGetFESpace(basis, &fe_space));
1728 
1729   // Print FE space and element topology of the basis
1730   fprintf(stream, "CeedBasis in a %s on a %s element\n", CeedFESpaces[fe_space], CeedElemTopologies[topo]);
1731   if (is_tensor_basis) {
1732     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P_1d, basis->Q_1d);
1733   } else {
1734     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P, basis->Q);
1735   }
1736   fprintf(stream, "  dimension: %" CeedInt_FMT "\n  field components: %" CeedInt_FMT "\n", basis->dim, basis->num_comp);
1737   // Print quadrature data, interpolation/gradient/divergence/curl of the basis
1738   if (is_tensor_basis) {  // tensor basis
1739     CeedInt           P_1d, Q_1d;
1740     const CeedScalar *q_ref_1d, *q_weight_1d, *interp_1d, *grad_1d;
1741 
1742     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
1743     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
1744     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
1745     CeedCall(CeedBasisGetQWeights(basis, &q_weight_1d));
1746     CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
1747     CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
1748 
1749     CeedCall(CeedScalarView("qref1d", "\t% 12.8f", 1, Q_1d, q_ref_1d, stream));
1750     CeedCall(CeedScalarView("qweight1d", "\t% 12.8f", 1, Q_1d, q_weight_1d, stream));
1751     CeedCall(CeedScalarView("interp1d", "\t% 12.8f", Q_1d, P_1d, interp_1d, stream));
1752     CeedCall(CeedScalarView("grad1d", "\t% 12.8f", Q_1d, P_1d, grad_1d, stream));
1753   } else {  // non-tensor basis
1754     CeedInt           P, Q, dim, q_comp;
1755     const CeedScalar *q_ref, *q_weight, *interp, *grad, *div, *curl;
1756 
1757     CeedCall(CeedBasisGetNumNodes(basis, &P));
1758     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &Q));
1759     CeedCall(CeedBasisGetDimension(basis, &dim));
1760     CeedCall(CeedBasisGetQRef(basis, &q_ref));
1761     CeedCall(CeedBasisGetQWeights(basis, &q_weight));
1762     CeedCall(CeedBasisGetInterp(basis, &interp));
1763     CeedCall(CeedBasisGetGrad(basis, &grad));
1764     CeedCall(CeedBasisGetDiv(basis, &div));
1765     CeedCall(CeedBasisGetCurl(basis, &curl));
1766 
1767     CeedCall(CeedScalarView("qref", "\t% 12.8f", 1, Q * dim, q_ref, stream));
1768     CeedCall(CeedScalarView("qweight", "\t% 12.8f", 1, Q, q_weight, stream));
1769     CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_INTERP, &q_comp));
1770     CeedCall(CeedScalarView("interp", "\t% 12.8f", q_comp * Q, P, interp, stream));
1771     if (grad) {
1772       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_GRAD, &q_comp));
1773       CeedCall(CeedScalarView("grad", "\t% 12.8f", q_comp * Q, P, grad, stream));
1774     }
1775     if (div) {
1776       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_DIV, &q_comp));
1777       CeedCall(CeedScalarView("div", "\t% 12.8f", q_comp * Q, P, div, stream));
1778     }
1779     if (curl) {
1780       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_CURL, &q_comp));
1781       CeedCall(CeedScalarView("curl", "\t% 12.8f", q_comp * Q, P, curl, stream));
1782     }
1783   }
1784   return CEED_ERROR_SUCCESS;
1785 }
1786 
1787 /**
1788   @brief Check input vector dimensions for CeedBasisApply[Add]
1789 
1790   @param[in]  basis     `CeedBasis` to evaluate
1791   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1792                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1793   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1794                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1795   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1796                           @ref CEED_EVAL_INTERP to use interpolated values,
1797                           @ref CEED_EVAL_GRAD to use gradients,
1798                           @ref CEED_EVAL_DIV to use divergence,
1799                           @ref CEED_EVAL_CURL to use curl,
1800                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1801   @param[in]  u         Input `CeedVector`
1802   @param[out] v         Output `CeedVector`
1803 
1804   @return An error code: 0 - success, otherwise - failure
1805 
1806   @ref Developer
1807 **/
1808 static int CeedBasisApplyCheckDims(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1809   CeedInt  dim, num_comp, q_comp, num_nodes, num_qpts;
1810   CeedSize u_length = 0, v_length;
1811   Ceed     ceed;
1812 
1813   CeedCall(CeedBasisGetCeed(basis, &ceed));
1814   CeedCall(CeedBasisGetDimension(basis, &dim));
1815   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1816   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
1817   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1818   CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
1819   CeedCall(CeedVectorGetLength(v, &v_length));
1820   if (u) CeedCall(CeedVectorGetLength(u, &u_length));
1821 
1822   // Check compatibility of topological and geometrical dimensions
1823   CeedCheck((t_mode == CEED_TRANSPOSE && v_length % num_nodes == 0 && u_length % num_qpts == 0) ||
1824                 (t_mode == CEED_NOTRANSPOSE && u_length % num_nodes == 0 && v_length % num_qpts == 0),
1825             ceed, CEED_ERROR_DIMENSION, "Length of input/output vectors incompatible with basis dimensions");
1826 
1827   // Check vector lengths to prevent out of bounds issues
1828   bool has_good_dims = true;
1829   switch (eval_mode) {
1830     case CEED_EVAL_NONE:
1831     case CEED_EVAL_INTERP:
1832     case CEED_EVAL_GRAD:
1833     case CEED_EVAL_DIV:
1834     case CEED_EVAL_CURL:
1835       has_good_dims =
1836           ((t_mode == CEED_TRANSPOSE && u_length >= num_elem * num_comp * num_qpts * q_comp && v_length >= num_elem * num_comp * num_nodes) ||
1837            (t_mode == CEED_NOTRANSPOSE && v_length >= num_elem * num_qpts * num_comp * q_comp && u_length >= num_elem * num_comp * num_nodes));
1838       break;
1839     case CEED_EVAL_WEIGHT:
1840       has_good_dims = v_length >= num_elem * num_qpts;
1841       break;
1842   }
1843   CeedCheck(has_good_dims, ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
1844   return CEED_ERROR_SUCCESS;
1845 }
1846 
1847 /**
1848   @brief Apply basis evaluation from nodes to quadrature points or vice versa
1849 
1850   @param[in]  basis     `CeedBasis` to evaluate
1851   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1852                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1853   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1854                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1855   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1856                           @ref CEED_EVAL_INTERP to use interpolated values,
1857                           @ref CEED_EVAL_GRAD to use gradients,
1858                           @ref CEED_EVAL_DIV to use divergence,
1859                           @ref CEED_EVAL_CURL to use curl,
1860                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1861   @param[in]  u         Input `CeedVector`
1862   @param[out] v         Output `CeedVector`
1863 
1864   @return An error code: 0 - success, otherwise - failure
1865 
1866   @ref User
1867 **/
1868 int CeedBasisApply(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1869   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
1870   CeedCheck(basis->Apply, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not support CeedBasisApply");
1871   CeedCall(basis->Apply(basis, num_elem, t_mode, eval_mode, u, v));
1872   return CEED_ERROR_SUCCESS;
1873 }
1874 
1875 /**
1876   @brief Apply basis evaluation from quadrature points to nodes and sum into target vector
1877 
1878   @param[in]  basis     `CeedBasis` to evaluate
1879   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1880                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1881   @param[in]  t_mode    @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes;
1882                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAdd()`
1883   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1884                           @ref CEED_EVAL_INTERP to use interpolated values,
1885                           @ref CEED_EVAL_GRAD to use gradients,
1886                           @ref CEED_EVAL_DIV to use divergence,
1887                           @ref CEED_EVAL_CURL to use curl,
1888                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1889   @param[in]  u         Input `CeedVector`
1890   @param[out] v         Output `CeedVector` to sum into
1891 
1892   @return An error code: 0 - success, otherwise - failure
1893 
1894   @ref User
1895 **/
1896 int CeedBasisApplyAdd(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1897   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAdd only supports CEED_TRANSPOSE");
1898   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
1899   CeedCheck(basis->ApplyAdd, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not implement CeedBasisApplyAdd");
1900   CeedCall(basis->ApplyAdd(basis, num_elem, t_mode, eval_mode, u, v));
1901   return CEED_ERROR_SUCCESS;
1902 }
1903 
1904 /**
1905   @brief Apply basis evaluation from nodes to arbitrary points
1906 
1907   @param[in]  basis      `CeedBasis` to evaluate
1908   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
1909                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1910   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
1911   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1912                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
1913   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
1914                            @ref CEED_EVAL_GRAD to use gradients,
1915                            @ref CEED_EVAL_WEIGHT to use quadrature weights
1916   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
1917   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
1918   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
1919 
1920   @return An error code: 0 - success, otherwise - failure
1921 
1922   @ref User
1923 **/
1924 int CeedBasisApplyAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
1925                            CeedVector x_ref, CeedVector u, CeedVector v) {
1926   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1927   if (basis->ApplyAtPoints) {
1928     CeedCall(basis->ApplyAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1929   } else {
1930     CeedCall(CeedBasisApplyAtPoints_Core(basis, false, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1931   }
1932   return CEED_ERROR_SUCCESS;
1933 }
1934 
1935 /**
1936   @brief Apply basis evaluation from nodes to arbitrary points and sum into target vector
1937 
1938   @param[in]  basis      `CeedBasis` to evaluate
1939   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
1940                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1941   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
1942   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1943                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAddAtPoints()`
1944   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
1945                            @ref CEED_EVAL_GRAD to use gradients,
1946                            @ref CEED_EVAL_WEIGHT to use quadrature weights
1947   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
1948   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
1949   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
1950 
1951   @return An error code: 0 - success, otherwise - failure
1952 
1953   @ref User
1954 **/
1955 int CeedBasisApplyAddAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
1956                               CeedVector x_ref, CeedVector u, CeedVector v) {
1957   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAddAtPoints only supports CEED_TRANSPOSE");
1958   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1959   if (basis->ApplyAddAtPoints) {
1960     CeedCall(basis->ApplyAddAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1961   } else {
1962     CeedCall(CeedBasisApplyAtPoints_Core(basis, true, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1963   }
1964   return CEED_ERROR_SUCCESS;
1965 }
1966 
1967 /**
1968   @brief Get the `Ceed` associated with a `CeedBasis`
1969 
1970   @param[in]  basis `CeedBasis`
1971   @param[out] ceed  Variable to store `Ceed`
1972 
1973   @return An error code: 0 - success, otherwise - failure
1974 
1975   @ref Advanced
1976 **/
1977 int CeedBasisGetCeed(CeedBasis basis, Ceed *ceed) {
1978   *ceed = CeedBasisReturnCeed(basis);
1979   return CEED_ERROR_SUCCESS;
1980 }
1981 
1982 /**
1983   @brief Return the `Ceed` associated with a `CeedBasis`
1984 
1985   @param[in]  basis `CeedBasis`
1986 
1987   @return `Ceed` associated with the `basis`
1988 
1989   @ref Advanced
1990 **/
1991 Ceed CeedBasisReturnCeed(CeedBasis basis) { return basis->ceed; }
1992 
1993 /**
1994   @brief Get dimension for given `CeedBasis`
1995 
1996   @param[in]  basis `CeedBasis`
1997   @param[out] dim   Variable to store dimension of basis
1998 
1999   @return An error code: 0 - success, otherwise - failure
2000 
2001   @ref Advanced
2002 **/
2003 int CeedBasisGetDimension(CeedBasis basis, CeedInt *dim) {
2004   *dim = basis->dim;
2005   return CEED_ERROR_SUCCESS;
2006 }
2007 
2008 /**
2009   @brief Get topology for given `CeedBasis`
2010 
2011   @param[in]  basis `CeedBasis`
2012   @param[out] topo  Variable to store topology of basis
2013 
2014   @return An error code: 0 - success, otherwise - failure
2015 
2016   @ref Advanced
2017 **/
2018 int CeedBasisGetTopology(CeedBasis basis, CeedElemTopology *topo) {
2019   *topo = basis->topo;
2020   return CEED_ERROR_SUCCESS;
2021 }
2022 
2023 /**
2024   @brief Get number of components for given `CeedBasis`
2025 
2026   @param[in]  basis    `CeedBasis`
2027   @param[out] num_comp Variable to store number of components
2028 
2029   @return An error code: 0 - success, otherwise - failure
2030 
2031   @ref Advanced
2032 **/
2033 int CeedBasisGetNumComponents(CeedBasis basis, CeedInt *num_comp) {
2034   *num_comp = basis->num_comp;
2035   return CEED_ERROR_SUCCESS;
2036 }
2037 
2038 /**
2039   @brief Get total number of nodes (in `dim` dimensions) of a `CeedBasis`
2040 
2041   @param[in]  basis `CeedBasis`
2042   @param[out] P     Variable to store number of nodes
2043 
2044   @return An error code: 0 - success, otherwise - failure
2045 
2046   @ref Utility
2047 **/
2048 int CeedBasisGetNumNodes(CeedBasis basis, CeedInt *P) {
2049   *P = basis->P;
2050   return CEED_ERROR_SUCCESS;
2051 }
2052 
2053 /**
2054   @brief Get total number of nodes (in 1 dimension) of a `CeedBasis`
2055 
2056   @param[in]  basis `CeedBasis`
2057   @param[out] P_1d  Variable to store number of nodes
2058 
2059   @return An error code: 0 - success, otherwise - failure
2060 
2061   @ref Advanced
2062 **/
2063 int CeedBasisGetNumNodes1D(CeedBasis basis, CeedInt *P_1d) {
2064   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply P_1d for non-tensor CeedBasis");
2065   *P_1d = basis->P_1d;
2066   return CEED_ERROR_SUCCESS;
2067 }
2068 
2069 /**
2070   @brief Get total number of quadrature points (in `dim` dimensions) of a `CeedBasis`
2071 
2072   @param[in]  basis `CeedBasis`
2073   @param[out] Q     Variable to store number of quadrature points
2074 
2075   @return An error code: 0 - success, otherwise - failure
2076 
2077   @ref Utility
2078 **/
2079 int CeedBasisGetNumQuadraturePoints(CeedBasis basis, CeedInt *Q) {
2080   *Q = basis->Q;
2081   return CEED_ERROR_SUCCESS;
2082 }
2083 
2084 /**
2085   @brief Get total number of quadrature points (in 1 dimension) of a `CeedBasis`
2086 
2087   @param[in]  basis `CeedBasis`
2088   @param[out] Q_1d  Variable to store number of quadrature points
2089 
2090   @return An error code: 0 - success, otherwise - failure
2091 
2092   @ref Advanced
2093 **/
2094 int CeedBasisGetNumQuadraturePoints1D(CeedBasis basis, CeedInt *Q_1d) {
2095   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply Q_1d for non-tensor CeedBasis");
2096   *Q_1d = basis->Q_1d;
2097   return CEED_ERROR_SUCCESS;
2098 }
2099 
2100 /**
2101   @brief Get reference coordinates of quadrature points (in `dim` dimensions) of a `CeedBasis`
2102 
2103   @param[in]  basis `CeedBasis`
2104   @param[out] q_ref Variable to store reference coordinates of quadrature points
2105 
2106   @return An error code: 0 - success, otherwise - failure
2107 
2108   @ref Advanced
2109 **/
2110 int CeedBasisGetQRef(CeedBasis basis, const CeedScalar **q_ref) {
2111   *q_ref = basis->q_ref_1d;
2112   return CEED_ERROR_SUCCESS;
2113 }
2114 
2115 /**
2116   @brief Get quadrature weights of quadrature points (in `dim` dimensions) of a `CeedBasis`
2117 
2118   @param[in]  basis    `CeedBasis`
2119   @param[out] q_weight Variable to store quadrature weights
2120 
2121   @return An error code: 0 - success, otherwise - failure
2122 
2123   @ref Advanced
2124 **/
2125 int CeedBasisGetQWeights(CeedBasis basis, const CeedScalar **q_weight) {
2126   *q_weight = basis->q_weight_1d;
2127   return CEED_ERROR_SUCCESS;
2128 }
2129 
2130 /**
2131   @brief Get interpolation matrix of a `CeedBasis`
2132 
2133   @param[in]  basis  `CeedBasis`
2134   @param[out] interp Variable to store interpolation matrix
2135 
2136   @return An error code: 0 - success, otherwise - failure
2137 
2138   @ref Advanced
2139 **/
2140 int CeedBasisGetInterp(CeedBasis basis, const CeedScalar **interp) {
2141   if (!basis->interp && basis->is_tensor_basis) {
2142     // Allocate
2143     CeedCall(CeedMalloc(basis->Q * basis->P, &basis->interp));
2144 
2145     // Initialize
2146     for (CeedInt i = 0; i < basis->Q * basis->P; i++) basis->interp[i] = 1.0;
2147 
2148     // Calculate
2149     for (CeedInt d = 0; d < basis->dim; d++) {
2150       for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2151         for (CeedInt node = 0; node < basis->P; node++) {
2152           CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2153           CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2154 
2155           basis->interp[qpt * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2156         }
2157       }
2158     }
2159   }
2160   *interp = basis->interp;
2161   return CEED_ERROR_SUCCESS;
2162 }
2163 
2164 /**
2165   @brief Get 1D interpolation matrix of a tensor product `CeedBasis`
2166 
2167   @param[in]  basis     `CeedBasis`
2168   @param[out] interp_1d Variable to store interpolation matrix
2169 
2170   @return An error code: 0 - success, otherwise - failure
2171 
2172   @ref Backend
2173 **/
2174 int CeedBasisGetInterp1D(CeedBasis basis, const CeedScalar **interp_1d) {
2175   bool is_tensor_basis;
2176 
2177   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2178   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2179   *interp_1d = basis->interp_1d;
2180   return CEED_ERROR_SUCCESS;
2181 }
2182 
2183 /**
2184   @brief Get gradient matrix of a `CeedBasis`
2185 
2186   @param[in]  basis `CeedBasis`
2187   @param[out] grad  Variable to store gradient matrix
2188 
2189   @return An error code: 0 - success, otherwise - failure
2190 
2191   @ref Advanced
2192 **/
2193 int CeedBasisGetGrad(CeedBasis basis, const CeedScalar **grad) {
2194   if (!basis->grad && basis->is_tensor_basis) {
2195     // Allocate
2196     CeedCall(CeedMalloc(basis->dim * basis->Q * basis->P, &basis->grad));
2197 
2198     // Initialize
2199     for (CeedInt i = 0; i < basis->dim * basis->Q * basis->P; i++) basis->grad[i] = 1.0;
2200 
2201     // Calculate
2202     for (CeedInt d = 0; d < basis->dim; d++) {
2203       for (CeedInt i = 0; i < basis->dim; i++) {
2204         for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2205           for (CeedInt node = 0; node < basis->P; node++) {
2206             CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2207             CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2208 
2209             if (i == d) basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->grad_1d[q * basis->P_1d + p];
2210             else basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2211           }
2212         }
2213       }
2214     }
2215   }
2216   *grad = basis->grad;
2217   return CEED_ERROR_SUCCESS;
2218 }
2219 
2220 /**
2221   @brief Get 1D gradient matrix of a tensor product `CeedBasis`
2222 
2223   @param[in]  basis   `CeedBasis`
2224   @param[out] grad_1d Variable to store gradient matrix
2225 
2226   @return An error code: 0 - success, otherwise - failure
2227 
2228   @ref Advanced
2229 **/
2230 int CeedBasisGetGrad1D(CeedBasis basis, const CeedScalar **grad_1d) {
2231   bool is_tensor_basis;
2232 
2233   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2234   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2235   *grad_1d = basis->grad_1d;
2236   return CEED_ERROR_SUCCESS;
2237 }
2238 
2239 /**
2240   @brief Get divergence matrix of a `CeedBasis`
2241 
2242   @param[in]  basis `CeedBasis`
2243   @param[out] div   Variable to store divergence matrix
2244 
2245   @return An error code: 0 - success, otherwise - failure
2246 
2247   @ref Advanced
2248 **/
2249 int CeedBasisGetDiv(CeedBasis basis, const CeedScalar **div) {
2250   *div = basis->div;
2251   return CEED_ERROR_SUCCESS;
2252 }
2253 
2254 /**
2255   @brief Get curl matrix of a `CeedBasis`
2256 
2257   @param[in]  basis `CeedBasis`
2258   @param[out] curl  Variable to store curl matrix
2259 
2260   @return An error code: 0 - success, otherwise - failure
2261 
2262   @ref Advanced
2263 **/
2264 int CeedBasisGetCurl(CeedBasis basis, const CeedScalar **curl) {
2265   *curl = basis->curl;
2266   return CEED_ERROR_SUCCESS;
2267 }
2268 
2269 /**
2270   @brief Destroy a @ref  CeedBasis
2271 
2272   @param[in,out] basis `CeedBasis` to destroy
2273 
2274   @return An error code: 0 - success, otherwise - failure
2275 
2276   @ref User
2277 **/
2278 int CeedBasisDestroy(CeedBasis *basis) {
2279   if (!*basis || *basis == CEED_BASIS_NONE || --(*basis)->ref_count > 0) {
2280     *basis = NULL;
2281     return CEED_ERROR_SUCCESS;
2282   }
2283   if ((*basis)->Destroy) CeedCall((*basis)->Destroy(*basis));
2284   CeedCall(CeedTensorContractDestroy(&(*basis)->contract));
2285   CeedCall(CeedFree(&(*basis)->q_ref_1d));
2286   CeedCall(CeedFree(&(*basis)->q_weight_1d));
2287   CeedCall(CeedFree(&(*basis)->interp));
2288   CeedCall(CeedFree(&(*basis)->interp_1d));
2289   CeedCall(CeedFree(&(*basis)->grad));
2290   CeedCall(CeedFree(&(*basis)->grad_1d));
2291   CeedCall(CeedFree(&(*basis)->div));
2292   CeedCall(CeedFree(&(*basis)->curl));
2293   CeedCall(CeedVectorDestroy(&(*basis)->vec_chebyshev));
2294   CeedCall(CeedBasisDestroy(&(*basis)->basis_chebyshev));
2295   CeedCall(CeedDestroy(&(*basis)->ceed));
2296   CeedCall(CeedFree(basis));
2297   return CEED_ERROR_SUCCESS;
2298 }
2299 
2300 /**
2301   @brief Construct a Gauss-Legendre quadrature
2302 
2303   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-1` exactly)
2304   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2305   @param[out] q_weight_1d Array of length `Q` to hold the weights
2306 
2307   @return An error code: 0 - success, otherwise - failure
2308 
2309   @ref Utility
2310 **/
2311 int CeedGaussQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2312   CeedScalar P0, P1, P2, dP2, xi, wi, PI = 4.0 * atan(1.0);
2313 
2314   // Build q_ref_1d, q_weight_1d
2315   for (CeedInt i = 0; i <= Q / 2; i++) {
2316     // Guess
2317     xi = cos(PI * (CeedScalar)(2 * i + 1) / ((CeedScalar)(2 * Q)));
2318     // Pn(xi)
2319     P0 = 1.0;
2320     P1 = xi;
2321     P2 = 0.0;
2322     for (CeedInt j = 2; j <= Q; j++) {
2323       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2324       P0 = P1;
2325       P1 = P2;
2326     }
2327     // First Newton Step
2328     dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2329     xi  = xi - P2 / dP2;
2330     // Newton to convergence
2331     for (CeedInt k = 0; k < 100 && fabs(P2) > 10 * CEED_EPSILON; k++) {
2332       P0 = 1.0;
2333       P1 = xi;
2334       for (CeedInt j = 2; j <= Q; j++) {
2335         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2336         P0 = P1;
2337         P1 = P2;
2338       }
2339       dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2340       xi  = xi - P2 / dP2;
2341     }
2342     // Save xi, wi
2343     wi                     = 2.0 / ((1.0 - xi * xi) * dP2 * dP2);
2344     q_weight_1d[i]         = wi;
2345     q_weight_1d[Q - 1 - i] = wi;
2346     q_ref_1d[i]            = -xi;
2347     q_ref_1d[Q - 1 - i]    = xi;
2348   }
2349   return CEED_ERROR_SUCCESS;
2350 }
2351 
2352 /**
2353   @brief Construct a Gauss-Legendre-Lobatto quadrature
2354 
2355   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-3` exactly)
2356   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2357   @param[out] q_weight_1d Array of length `Q` to hold the weights
2358 
2359   @return An error code: 0 - success, otherwise - failure
2360 
2361   @ref Utility
2362 **/
2363 int CeedLobattoQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2364   CeedScalar P0, P1, P2, dP2, d2P2, xi, wi, PI = 4.0 * atan(1.0);
2365 
2366   // Build q_ref_1d, q_weight_1d
2367   // Set endpoints
2368   CeedCheck(Q > 1, NULL, CEED_ERROR_DIMENSION, "Cannot create Lobatto quadrature with Q=%" CeedInt_FMT " < 2 points", Q);
2369   wi = 2.0 / ((CeedScalar)(Q * (Q - 1)));
2370   if (q_weight_1d) {
2371     q_weight_1d[0]     = wi;
2372     q_weight_1d[Q - 1] = wi;
2373   }
2374   q_ref_1d[0]     = -1.0;
2375   q_ref_1d[Q - 1] = 1.0;
2376   // Interior
2377   for (CeedInt i = 1; i <= (Q - 1) / 2; i++) {
2378     // Guess
2379     xi = cos(PI * (CeedScalar)(i) / (CeedScalar)(Q - 1));
2380     // Pn(xi)
2381     P0 = 1.0;
2382     P1 = xi;
2383     P2 = 0.0;
2384     for (CeedInt j = 2; j < Q; j++) {
2385       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2386       P0 = P1;
2387       P1 = P2;
2388     }
2389     // First Newton step
2390     dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2391     d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2392     xi   = xi - dP2 / d2P2;
2393     // Newton to convergence
2394     for (CeedInt k = 0; k < 100 && fabs(dP2) > 10 * CEED_EPSILON; k++) {
2395       P0 = 1.0;
2396       P1 = xi;
2397       for (CeedInt j = 2; j < Q; j++) {
2398         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2399         P0 = P1;
2400         P1 = P2;
2401       }
2402       dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2403       d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2404       xi   = xi - dP2 / d2P2;
2405     }
2406     // Save xi, wi
2407     wi = 2.0 / (((CeedScalar)(Q * (Q - 1))) * P2 * P2);
2408     if (q_weight_1d) {
2409       q_weight_1d[i]         = wi;
2410       q_weight_1d[Q - 1 - i] = wi;
2411     }
2412     q_ref_1d[i]         = -xi;
2413     q_ref_1d[Q - 1 - i] = xi;
2414   }
2415   return CEED_ERROR_SUCCESS;
2416 }
2417 
2418 /// @}
2419