xref: /libCEED/interface/ceed-basis.c (revision 8bbba8cdca038b4242f0cbb369bb1e31b8a6e289)
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 coordinates vector
335   for (CeedInt i = 0; i < num_elem; i++) total_num_points += num_points[i];
336   CeedCheck((x_length >= total_num_points * dim) || (eval_mode == CEED_EVAL_WEIGHT), ceed, CEED_ERROR_DIMENSION,
337             "Length of reference coordinate vector incompatible with basis dimension and number of points."
338             " Found reference coordinate vector of length %" CeedSize_FMT ", not of length %" CeedSize_FMT ".",
339             x_length, total_num_points * dim);
340 
341   // Check CEED_EVAL_WEIGHT only on CEED_NOTRANSPOSE
342   CeedCheck(eval_mode != CEED_EVAL_WEIGHT || t_mode == CEED_NOTRANSPOSE, ceed, CEED_ERROR_UNSUPPORTED,
343             "CEED_EVAL_WEIGHT only supported with CEED_NOTRANSPOSE");
344 
345   // Check vector lengths to prevent out of bounds issues
346   bool has_good_dims = true;
347   switch (eval_mode) {
348     case CEED_EVAL_INTERP:
349       has_good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= total_num_points * num_q_comp || v_length >= num_elem * num_nodes * num_comp)) ||
350                        (t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points * num_q_comp || u_length >= num_elem * num_nodes * num_comp)));
351       break;
352     case CEED_EVAL_GRAD:
353       has_good_dims =
354           ((t_mode == CEED_TRANSPOSE && (u_length >= total_num_points * num_q_comp * dim || v_length >= num_elem * num_nodes * num_comp)) ||
355            (t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points * num_q_comp * dim || u_length >= num_elem * num_nodes * num_comp)));
356       break;
357     case CEED_EVAL_WEIGHT:
358       has_good_dims = t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points);
359       break;
360       // LCOV_EXCL_START
361     case CEED_EVAL_NONE:
362     case CEED_EVAL_DIV:
363     case CEED_EVAL_CURL:
364       return CeedError(ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points not supported for %s", CeedEvalModes[eval_mode]);
365       // LCOV_EXCL_STOP
366   }
367   CeedCheck(has_good_dims, ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
368   return CEED_ERROR_SUCCESS;
369 }
370 
371 /**
372   @brief Default implimentation to apply basis evaluation from nodes to arbitrary points
373 
374   @param[in]  basis      `CeedBasis` to evaluate
375   @param[in]  apply_add  Sum result into target vector or overwrite
376   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
377                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
378   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
379   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
380                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
381   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
382                            @ref CEED_EVAL_GRAD to use gradients,
383                            @ref CEED_EVAL_WEIGHT to use quadrature weights
384   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
385   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
386   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
387 
388   @return An error code: 0 - success, otherwise - failure
389 
390   @ref Developer
391 **/
392 static int CeedBasisApplyAtPoints_Core(CeedBasis basis, bool apply_add, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode,
393                                        CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u, CeedVector v) {
394   CeedInt dim, num_comp, P_1d = 1, Q_1d = 1, total_num_points = num_points[0];
395   Ceed    ceed;
396 
397   CeedCall(CeedBasisGetCeed(basis, &ceed));
398   CeedCall(CeedBasisGetDimension(basis, &dim));
399   // Inserting check because clang-tidy doesn't understand this cannot occur
400   CeedCheck(dim > 0, ceed, CEED_ERROR_UNSUPPORTED, "Malformed CeedBasis, dim > 0 is required");
401   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
402   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
403   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
404 
405   // Default implementation
406   {
407     bool is_tensor_basis;
408 
409     CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
410     CeedCheck(is_tensor_basis, ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points only supported for tensor product bases");
411   }
412   CeedCheck(num_elem == 1, ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary  points only supported for a single element at a time");
413   if (eval_mode == CEED_EVAL_WEIGHT) {
414     CeedCall(CeedVectorSetValue(v, 1.0));
415     return CEED_ERROR_SUCCESS;
416   }
417   if (!basis->basis_chebyshev) {
418     // Build basis mapping from nodes to Chebyshev coefficients
419     CeedScalar       *chebyshev_interp_1d, *chebyshev_grad_1d, *chebyshev_q_weight_1d;
420     const CeedScalar *q_ref_1d;
421 
422     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_interp_1d));
423     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_grad_1d));
424     CeedCall(CeedCalloc(Q_1d, &chebyshev_q_weight_1d));
425     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
426     CeedCall(CeedBasisGetChebyshevInterp1D(basis, chebyshev_interp_1d));
427 
428     CeedCall(CeedVectorCreate(ceed, num_comp * CeedIntPow(Q_1d, dim), &basis->vec_chebyshev));
429     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d, Q_1d, chebyshev_interp_1d, chebyshev_grad_1d, q_ref_1d, chebyshev_q_weight_1d,
430                                      &basis->basis_chebyshev));
431 
432     // Cleanup
433     CeedCall(CeedFree(&chebyshev_interp_1d));
434     CeedCall(CeedFree(&chebyshev_grad_1d));
435     CeedCall(CeedFree(&chebyshev_q_weight_1d));
436   }
437 
438   // Create TensorContract object if needed, such as a basis from the GPU backends
439   if (!basis->contract) {
440     Ceed      ceed_ref;
441     CeedBasis basis_ref = NULL;
442 
443     CeedCall(CeedInit("/cpu/self", &ceed_ref));
444     // Only need matching tensor contraction dimensions, any type of basis will work
445     CeedCall(CeedBasisCreateTensorH1Lagrange(ceed_ref, dim, num_comp, P_1d, Q_1d, CEED_GAUSS, &basis_ref));
446     // Note - clang-tidy doesn't know basis_ref->contract must be valid here
447     CeedCheck(basis_ref && basis_ref->contract, ceed, CEED_ERROR_UNSUPPORTED, "Reference CPU ceed failed to create a tensor contraction object");
448     CeedCall(CeedTensorContractReferenceCopy(basis_ref->contract, &basis->contract));
449     CeedCall(CeedBasisDestroy(&basis_ref));
450     CeedCall(CeedDestroy(&ceed_ref));
451   }
452 
453   // Basis evaluation
454   switch (t_mode) {
455     case CEED_NOTRANSPOSE: {
456       // Nodes to arbitrary points
457       CeedScalar       *v_array;
458       const CeedScalar *chebyshev_coeffs, *x_array_read;
459 
460       // -- Interpolate to Chebyshev coefficients
461       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_NOTRANSPOSE, CEED_EVAL_INTERP, u, basis->vec_chebyshev));
462 
463       // -- Evaluate Chebyshev polynomials at arbitrary points
464       CeedCall(CeedVectorGetArrayRead(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
465       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
466       CeedCall(CeedVectorGetArrayWrite(v, CEED_MEM_HOST, &v_array));
467       switch (eval_mode) {
468         case CEED_EVAL_INTERP: {
469           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
470 
471           // ---- Values at point
472           for (CeedInt p = 0; p < total_num_points; p++) {
473             CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
474 
475             for (CeedInt d = 0; d < dim; d++) {
476               // ------ Tensor contract with current Chebyshev polynomial values
477               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
478               CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
479                                                d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
480               pre /= Q_1d;
481               post *= 1;
482             }
483             for (CeedInt c = 0; c < num_comp; c++) v_array[c * total_num_points + p] = tmp[dim % 2][c];
484           }
485           break;
486         }
487         case CEED_EVAL_GRAD: {
488           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
489 
490           // ---- Values at point
491           for (CeedInt p = 0; p < total_num_points; p++) {
492             // Dim**2 contractions, apply grad when pass == dim
493             for (CeedInt pass = 0; pass < dim; pass++) {
494               CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
495 
496               for (CeedInt d = 0; d < dim; d++) {
497                 // ------ Tensor contract with current Chebyshev polynomial values
498                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
499                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
500                 CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
501                                                  d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
502                 pre /= Q_1d;
503                 post *= 1;
504               }
505               for (CeedInt c = 0; c < num_comp; c++) v_array[(pass * num_comp + c) * total_num_points + p] = tmp[dim % 2][c];
506             }
507           }
508           break;
509         }
510         default:
511           // Nothing to do, excluded above
512           break;
513       }
514       CeedCall(CeedVectorRestoreArrayRead(basis->vec_chebyshev, &chebyshev_coeffs));
515       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
516       CeedCall(CeedVectorRestoreArray(v, &v_array));
517       break;
518     }
519     case CEED_TRANSPOSE: {
520       // Note: No switch on e_mode here because only CEED_EVAL_INTERP is supported at this time
521       // Arbitrary points to nodes
522       CeedScalar       *chebyshev_coeffs;
523       const CeedScalar *u_array, *x_array_read;
524 
525       // -- Transpose of evaluation of Chebyshev polynomials at arbitrary points
526       CeedCall(CeedVectorGetArrayWrite(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
527       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
528       CeedCall(CeedVectorGetArrayRead(u, CEED_MEM_HOST, &u_array));
529 
530       switch (eval_mode) {
531         case CEED_EVAL_INTERP: {
532           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
533 
534           // ---- Values at point
535           for (CeedInt p = 0; p < total_num_points; p++) {
536             CeedInt pre = num_comp * 1, post = 1;
537 
538             for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[c * total_num_points + p];
539             for (CeedInt d = 0; d < dim; d++) {
540               // ------ Tensor contract with current Chebyshev polynomial values
541               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
542               CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode, p > 0 && d == (dim - 1), tmp[d % 2],
543                                                d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
544               pre /= 1;
545               post *= Q_1d;
546             }
547           }
548           break;
549         }
550         case CEED_EVAL_GRAD: {
551           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
552 
553           // ---- Values at point
554           for (CeedInt p = 0; p < total_num_points; p++) {
555             // Dim**2 contractions, apply grad when pass == dim
556             for (CeedInt pass = 0; pass < dim; pass++) {
557               CeedInt pre = num_comp * 1, post = 1;
558 
559               for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[(pass * num_comp + c) * total_num_points + p];
560               for (CeedInt d = 0; d < dim; d++) {
561                 // ------ Tensor contract with current Chebyshev polynomial values
562                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
563                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
564                 CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode,
565                                                  (p > 0 || (p == 0 && pass > 0)) && d == (dim - 1), tmp[d % 2],
566                                                  d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
567                 pre /= 1;
568                 post *= Q_1d;
569               }
570             }
571           }
572           break;
573         }
574         default:
575           // Nothing to do, excluded above
576           break;
577       }
578       CeedCall(CeedVectorRestoreArray(basis->vec_chebyshev, &chebyshev_coeffs));
579       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
580       CeedCall(CeedVectorRestoreArrayRead(u, &u_array));
581 
582       // -- Interpolate transpose from Chebyshev coefficients
583       if (apply_add) CeedCall(CeedBasisApplyAdd(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
584       else CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
585       break;
586     }
587   }
588   return CEED_ERROR_SUCCESS;
589 }
590 
591 /// @}
592 
593 /// ----------------------------------------------------------------------------
594 /// Ceed Backend API
595 /// ----------------------------------------------------------------------------
596 /// @addtogroup CeedBasisBackend
597 /// @{
598 
599 /**
600   @brief Return collocated gradient matrix
601 
602   @param[in]  basis         `CeedBasis`
603   @param[out] collo_grad_1d Row-major (`Q_1d * Q_1d`) matrix expressing derivatives of basis functions at quadrature points
604 
605   @return An error code: 0 - success, otherwise - failure
606 
607   @ref Backend
608 **/
609 int CeedBasisGetCollocatedGrad(CeedBasis basis, CeedScalar *collo_grad_1d) {
610   Ceed              ceed;
611   CeedInt           P_1d, Q_1d;
612   CeedScalar       *interp_1d_pinv;
613   const CeedScalar *grad_1d, *interp_1d;
614 
615   // Note: This function is for backend use, so all errors are terminal and we do not need to clean up memory on failure.
616   CeedCall(CeedBasisGetCeed(basis, &ceed));
617   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
618   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
619 
620   // Compute interp_1d^+, pseudoinverse of interp_1d
621   CeedCall(CeedCalloc(P_1d * Q_1d, &interp_1d_pinv));
622   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
623   CeedCall(CeedMatrixPseudoinverse(ceed, interp_1d, Q_1d, P_1d, interp_1d_pinv));
624   CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
625   CeedCall(CeedMatrixMatrixMultiply(ceed, grad_1d, (const CeedScalar *)interp_1d_pinv, collo_grad_1d, Q_1d, Q_1d, P_1d));
626 
627   CeedCall(CeedFree(&interp_1d_pinv));
628   return CEED_ERROR_SUCCESS;
629 }
630 
631 /**
632   @brief Return 1D interpolation matrix to Chebyshev polynomial coefficients on quadrature space
633 
634   @param[in]  basis               `CeedBasis`
635   @param[out] chebyshev_interp_1d Row-major (`P_1d * Q_1d`) matrix interpolating from basis nodes to Chebyshev polynomial coefficients
636 
637   @return An error code: 0 - success, otherwise - failure
638 
639   @ref Backend
640 **/
641 int CeedBasisGetChebyshevInterp1D(CeedBasis basis, CeedScalar *chebyshev_interp_1d) {
642   CeedInt           P_1d, Q_1d;
643   CeedScalar       *C, *chebyshev_coeffs_1d_inv;
644   const CeedScalar *interp_1d, *q_ref_1d;
645   Ceed              ceed;
646 
647   CeedCall(CeedBasisGetCeed(basis, &ceed));
648   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
649   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
650 
651   // Build coefficient matrix
652   // -- Note: Clang-tidy needs this check
653   CeedCheck((P_1d > 0) && (Q_1d > 0), ceed, CEED_ERROR_INCOMPATIBLE, "CeedBasis dimensions are malformed");
654   CeedCall(CeedCalloc(Q_1d * Q_1d, &C));
655   CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
656   for (CeedInt i = 0; i < Q_1d; i++) CeedCall(CeedChebyshevPolynomialsAtPoint(q_ref_1d[i], Q_1d, &C[i * Q_1d]));
657 
658   // Compute C^+, pseudoinverse of coefficient matrix
659   CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_coeffs_1d_inv));
660   CeedCall(CeedMatrixPseudoinverse(ceed, C, Q_1d, Q_1d, chebyshev_coeffs_1d_inv));
661 
662   // Build mapping from nodes to Chebyshev coefficients
663   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
664   CeedCall(CeedMatrixMatrixMultiply(ceed, chebyshev_coeffs_1d_inv, interp_1d, chebyshev_interp_1d, Q_1d, P_1d, Q_1d));
665 
666   // Cleanup
667   CeedCall(CeedFree(&C));
668   CeedCall(CeedFree(&chebyshev_coeffs_1d_inv));
669   return CEED_ERROR_SUCCESS;
670 }
671 
672 /**
673   @brief Get tensor status for given `CeedBasis`
674 
675   @param[in]  basis     `CeedBasis`
676   @param[out] is_tensor Variable to store tensor status
677 
678   @return An error code: 0 - success, otherwise - failure
679 
680   @ref Backend
681 **/
682 int CeedBasisIsTensor(CeedBasis basis, bool *is_tensor) {
683   *is_tensor = basis->is_tensor_basis;
684   return CEED_ERROR_SUCCESS;
685 }
686 
687 /**
688   @brief Get backend data of a `CeedBasis`
689 
690   @param[in]  basis `CeedBasis`
691   @param[out] data  Variable to store data
692 
693   @return An error code: 0 - success, otherwise - failure
694 
695   @ref Backend
696 **/
697 int CeedBasisGetData(CeedBasis basis, void *data) {
698   *(void **)data = basis->data;
699   return CEED_ERROR_SUCCESS;
700 }
701 
702 /**
703   @brief Set backend data of a `CeedBasis`
704 
705   @param[in,out] basis  `CeedBasis`
706   @param[in]     data   Data to set
707 
708   @return An error code: 0 - success, otherwise - failure
709 
710   @ref Backend
711 **/
712 int CeedBasisSetData(CeedBasis basis, void *data) {
713   basis->data = data;
714   return CEED_ERROR_SUCCESS;
715 }
716 
717 /**
718   @brief Increment the reference counter for a `CeedBasis`
719 
720   @param[in,out] basis `CeedBasis` to increment the reference counter
721 
722   @return An error code: 0 - success, otherwise - failure
723 
724   @ref Backend
725 **/
726 int CeedBasisReference(CeedBasis basis) {
727   basis->ref_count++;
728   return CEED_ERROR_SUCCESS;
729 }
730 
731 /**
732   @brief Get number of Q-vector components for given `CeedBasis`
733 
734   @param[in]  basis     `CeedBasis`
735   @param[in]  eval_mode @ref CEED_EVAL_INTERP to use interpolated values,
736                           @ref CEED_EVAL_GRAD to use gradients,
737                           @ref CEED_EVAL_DIV to use divergence,
738                           @ref CEED_EVAL_CURL to use curl
739   @param[out] q_comp    Variable to store number of Q-vector components of basis
740 
741   @return An error code: 0 - success, otherwise - failure
742 
743   @ref Backend
744 **/
745 int CeedBasisGetNumQuadratureComponents(CeedBasis basis, CeedEvalMode eval_mode, CeedInt *q_comp) {
746   CeedInt dim;
747 
748   CeedCall(CeedBasisGetDimension(basis, &dim));
749   switch (eval_mode) {
750     case CEED_EVAL_INTERP: {
751       CeedFESpace fe_space;
752 
753       CeedCall(CeedBasisGetFESpace(basis, &fe_space));
754       *q_comp = (fe_space == CEED_FE_SPACE_H1) ? 1 : dim;
755     } break;
756     case CEED_EVAL_GRAD:
757       *q_comp = dim;
758       break;
759     case CEED_EVAL_DIV:
760       *q_comp = 1;
761       break;
762     case CEED_EVAL_CURL:
763       *q_comp = (dim < 3) ? 1 : dim;
764       break;
765     case CEED_EVAL_NONE:
766     case CEED_EVAL_WEIGHT:
767       *q_comp = 1;
768       break;
769   }
770   return CEED_ERROR_SUCCESS;
771 }
772 
773 /**
774   @brief Estimate number of FLOPs required to apply `CeedBasis` in `t_mode` and `eval_mode`
775 
776   @param[in]  basis     `CeedBasis` to estimate FLOPs for
777   @param[in]  t_mode    Apply basis or transpose
778   @param[in]  eval_mode @ref CeedEvalMode
779   @param[out] flops     Address of variable to hold FLOPs estimate
780 
781   @ref Backend
782 **/
783 int CeedBasisGetFlopsEstimate(CeedBasis basis, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedSize *flops) {
784   bool is_tensor;
785 
786   CeedCall(CeedBasisIsTensor(basis, &is_tensor));
787   if (is_tensor) {
788     CeedInt dim, num_comp, P_1d, Q_1d;
789 
790     CeedCall(CeedBasisGetDimension(basis, &dim));
791     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
792     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
793     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
794     if (t_mode == CEED_TRANSPOSE) {
795       P_1d = Q_1d;
796       Q_1d = P_1d;
797     }
798     CeedInt tensor_flops = 0, pre = num_comp * CeedIntPow(P_1d, dim - 1), post = 1;
799     for (CeedInt d = 0; d < dim; d++) {
800       tensor_flops += 2 * pre * P_1d * post * Q_1d;
801       pre /= P_1d;
802       post *= Q_1d;
803     }
804     switch (eval_mode) {
805       case CEED_EVAL_NONE:
806         *flops = 0;
807         break;
808       case CEED_EVAL_INTERP:
809         *flops = tensor_flops;
810         break;
811       case CEED_EVAL_GRAD:
812         *flops = tensor_flops * 2;
813         break;
814       case CEED_EVAL_DIV:
815       case CEED_EVAL_CURL: {
816         // LCOV_EXCL_START
817         return CeedError(CeedBasisReturnCeed(basis), CEED_ERROR_INCOMPATIBLE, "Tensor basis evaluation for %s not supported",
818                          CeedEvalModes[eval_mode]);
819         break;
820         // LCOV_EXCL_STOP
821       }
822       case CEED_EVAL_WEIGHT:
823         *flops = dim * CeedIntPow(Q_1d, dim);
824         break;
825     }
826   } else {
827     CeedInt dim, num_comp, q_comp, num_nodes, num_qpts;
828 
829     CeedCall(CeedBasisGetDimension(basis, &dim));
830     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
831     CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
832     CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
833     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
834     switch (eval_mode) {
835       case CEED_EVAL_NONE:
836         *flops = 0;
837         break;
838       case CEED_EVAL_INTERP:
839       case CEED_EVAL_GRAD:
840       case CEED_EVAL_DIV:
841       case CEED_EVAL_CURL:
842         *flops = num_nodes * num_qpts * num_comp * q_comp;
843         break;
844       case CEED_EVAL_WEIGHT:
845         *flops = 0;
846         break;
847     }
848   }
849   return CEED_ERROR_SUCCESS;
850 }
851 
852 /**
853   @brief Get `CeedFESpace` for a `CeedBasis`
854 
855   @param[in]  basis    `CeedBasis`
856   @param[out] fe_space Variable to store `CeedFESpace`
857 
858   @return An error code: 0 - success, otherwise - failure
859 
860   @ref Backend
861 **/
862 int CeedBasisGetFESpace(CeedBasis basis, CeedFESpace *fe_space) {
863   *fe_space = basis->fe_space;
864   return CEED_ERROR_SUCCESS;
865 }
866 
867 /**
868   @brief Get dimension for given `CeedElemTopology`
869 
870   @param[in]  topo `CeedElemTopology`
871   @param[out] dim  Variable to store dimension of topology
872 
873   @return An error code: 0 - success, otherwise - failure
874 
875   @ref Backend
876 **/
877 int CeedBasisGetTopologyDimension(CeedElemTopology topo, CeedInt *dim) {
878   *dim = (CeedInt)topo >> 16;
879   return CEED_ERROR_SUCCESS;
880 }
881 
882 /**
883   @brief Get `CeedTensorContract` of a `CeedBasis`
884 
885   @param[in]  basis     `CeedBasis`
886   @param[out] contract  Variable to store `CeedTensorContract`
887 
888   @return An error code: 0 - success, otherwise - failure
889 
890   @ref Backend
891 **/
892 int CeedBasisGetTensorContract(CeedBasis basis, CeedTensorContract *contract) {
893   *contract = basis->contract;
894   return CEED_ERROR_SUCCESS;
895 }
896 
897 /**
898   @brief Set `CeedTensorContract` of a `CeedBasis`
899 
900   @param[in,out] basis    `CeedBasis`
901   @param[in]     contract `CeedTensorContract` to set
902 
903   @return An error code: 0 - success, otherwise - failure
904 
905   @ref Backend
906 **/
907 int CeedBasisSetTensorContract(CeedBasis basis, CeedTensorContract contract) {
908   basis->contract = contract;
909   CeedCall(CeedTensorContractReference(contract));
910   return CEED_ERROR_SUCCESS;
911 }
912 
913 /**
914   @brief Return a reference implementation of matrix multiplication \f$C = A B\f$.
915 
916   Note: This is a reference implementation for CPU `CeedScalar` pointers that is not intended for high performance.
917 
918   @param[in]  ceed  `Ceed` context for error handling
919   @param[in]  mat_A Row-major matrix `A`
920   @param[in]  mat_B Row-major matrix `B`
921   @param[out] mat_C Row-major output matrix `C`
922   @param[in]  m     Number of rows of `C`
923   @param[in]  n     Number of columns of `C`
924   @param[in]  kk    Number of columns of `A`/rows of `B`
925 
926   @return An error code: 0 - success, otherwise - failure
927 
928   @ref Utility
929 **/
930 int CeedMatrixMatrixMultiply(Ceed ceed, const CeedScalar *mat_A, const CeedScalar *mat_B, CeedScalar *mat_C, CeedInt m, CeedInt n, CeedInt kk) {
931   for (CeedInt i = 0; i < m; i++) {
932     for (CeedInt j = 0; j < n; j++) {
933       CeedScalar sum = 0;
934 
935       for (CeedInt k = 0; k < kk; k++) sum += mat_A[k + i * kk] * mat_B[j + k * n];
936       mat_C[j + i * n] = sum;
937     }
938   }
939   return CEED_ERROR_SUCCESS;
940 }
941 
942 /**
943   @brief Return QR Factorization of a matrix
944 
945   @param[in]     ceed `Ceed` context for error handling
946   @param[in,out] mat  Row-major matrix to be factorized in place
947   @param[in,out] tau  Vector of length `m` of scaling factors
948   @param[in]     m    Number of rows
949   @param[in]     n    Number of columns
950 
951   @return An error code: 0 - success, otherwise - failure
952 
953   @ref Utility
954 **/
955 int CeedQRFactorization(Ceed ceed, CeedScalar *mat, CeedScalar *tau, CeedInt m, CeedInt n) {
956   CeedScalar v[m];
957 
958   // Check matrix shape
959   CeedCheck(n <= m, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute QR factorization with n > m");
960 
961   for (CeedInt i = 0; i < n; i++) {
962     CeedScalar sigma = 0.0;
963 
964     if (i >= m - 1) {  // last row of matrix, no reflection needed
965       tau[i] = 0.;
966       break;
967     }
968     // Calculate Householder vector, magnitude
969     v[i] = mat[i + n * i];
970     for (CeedInt j = i + 1; j < m; j++) {
971       v[j] = mat[i + n * j];
972       sigma += v[j] * v[j];
973     }
974     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:m]
975     const CeedScalar R_ii = -copysign(norm, v[i]);
976 
977     v[i] -= R_ii;
978     // norm of v[i:m] after modification above and scaling below
979     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
980     //   tau = 2 / (norm*norm)
981     tau[i] = 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
982     for (CeedInt j = i + 1; j < m; j++) v[j] /= v[i];
983 
984     // Apply Householder reflector to lower right panel
985     CeedHouseholderReflect(&mat[i * n + i + 1], &v[i], tau[i], m - i, n - i - 1, n, 1);
986     // Save v
987     mat[i + n * i] = R_ii;
988     for (CeedInt j = i + 1; j < m; j++) mat[i + n * j] = v[j];
989   }
990   return CEED_ERROR_SUCCESS;
991 }
992 
993 /**
994   @brief Apply Householder Q matrix
995 
996   Compute `mat_A = mat_Q mat_A`, where `mat_Q` is \f$m \times m\f$ and `mat_A` is \f$m \times n\f$.
997 
998   @param[in,out] mat_A  Matrix to apply Householder Q to, in place
999   @param[in]     mat_Q  Householder Q matrix
1000   @param[in]     tau    Householder scaling factors
1001   @param[in]     t_mode Transpose mode for application
1002   @param[in]     m      Number of rows in `A`
1003   @param[in]     n      Number of columns in `A`
1004   @param[in]     k      Number of elementary reflectors in Q, `k < m`
1005   @param[in]     row    Row stride in `A`
1006   @param[in]     col    Col stride in `A`
1007 
1008   @return An error code: 0 - success, otherwise - failure
1009 
1010   @ref Utility
1011 **/
1012 int CeedHouseholderApplyQ(CeedScalar *mat_A, const CeedScalar *mat_Q, const CeedScalar *tau, CeedTransposeMode t_mode, CeedInt m, CeedInt n,
1013                           CeedInt k, CeedInt row, CeedInt col) {
1014   CeedScalar *v;
1015 
1016   CeedCall(CeedMalloc(m, &v));
1017   for (CeedInt ii = 0; ii < k; ii++) {
1018     CeedInt i = t_mode == CEED_TRANSPOSE ? ii : k - 1 - ii;
1019     for (CeedInt j = i + 1; j < m; j++) v[j] = mat_Q[j * k + i];
1020     // Apply Householder reflector (I - tau v v^T) collo_grad_1d^T
1021     CeedCall(CeedHouseholderReflect(&mat_A[i * row], &v[i], tau[i], m - i, n, row, col));
1022   }
1023   CeedCall(CeedFree(&v));
1024   return CEED_ERROR_SUCCESS;
1025 }
1026 
1027 /**
1028   @brief Return pseudoinverse of a matrix
1029 
1030   @param[in]     ceed      Ceed context for error handling
1031   @param[in]     mat       Row-major matrix to compute pseudoinverse of
1032   @param[in]     m         Number of rows
1033   @param[in]     n         Number of columns
1034   @param[out]    mat_pinv  Row-major pseudoinverse matrix
1035 
1036   @return An error code: 0 - success, otherwise - failure
1037 
1038   @ref Utility
1039 **/
1040 int CeedMatrixPseudoinverse(Ceed ceed, const CeedScalar *mat, CeedInt m, CeedInt n, CeedScalar *mat_pinv) {
1041   CeedScalar *tau, *I, *mat_copy;
1042 
1043   CeedCall(CeedCalloc(m, &tau));
1044   CeedCall(CeedCalloc(m * m, &I));
1045   CeedCall(CeedCalloc(m * n, &mat_copy));
1046   memcpy(mat_copy, mat, m * n * sizeof mat[0]);
1047 
1048   // QR Factorization, mat = Q R
1049   CeedCall(CeedQRFactorization(ceed, mat_copy, tau, m, n));
1050 
1051   // -- Apply Q^T, I = Q^T * I
1052   for (CeedInt i = 0; i < m; i++) I[i * m + i] = 1.0;
1053   CeedCall(CeedHouseholderApplyQ(I, mat_copy, tau, CEED_TRANSPOSE, m, m, n, m, 1));
1054   // -- Apply R_inv, mat_pinv = R_inv * Q^T
1055   for (CeedInt j = 0; j < m; j++) {  // Column j
1056     mat_pinv[j + m * (n - 1)] = I[j + m * (n - 1)] / mat_copy[n * n - 1];
1057     for (CeedInt i = n - 2; i >= 0; i--) {  // Row i
1058       mat_pinv[j + m * i] = I[j + m * i];
1059       for (CeedInt k = i + 1; k < n; k++) mat_pinv[j + m * i] -= mat_copy[k + n * i] * mat_pinv[j + m * k];
1060       mat_pinv[j + m * i] /= mat_copy[i + n * i];
1061     }
1062   }
1063 
1064   // Cleanup
1065   CeedCall(CeedFree(&I));
1066   CeedCall(CeedFree(&tau));
1067   CeedCall(CeedFree(&mat_copy));
1068   return CEED_ERROR_SUCCESS;
1069 }
1070 
1071 /**
1072   @brief Return symmetric Schur decomposition of the symmetric matrix mat via symmetric QR factorization
1073 
1074   @param[in]     ceed   `Ceed` context for error handling
1075   @param[in,out] mat    Row-major matrix to be factorized in place
1076   @param[out]    lambda Vector of length n of eigenvalues
1077   @param[in]     n      Number of rows/columns
1078 
1079   @return An error code: 0 - success, otherwise - failure
1080 
1081   @ref Utility
1082 **/
1083 CeedPragmaOptimizeOff
1084 int CeedSymmetricSchurDecomposition(Ceed ceed, CeedScalar *mat, CeedScalar *lambda, CeedInt n) {
1085   // Check bounds for clang-tidy
1086   CeedCheck(n > 1, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute symmetric Schur decomposition of scalars");
1087 
1088   CeedScalar v[n - 1], tau[n - 1], mat_T[n * n];
1089 
1090   // Copy mat to mat_T and set mat to I
1091   memcpy(mat_T, mat, n * n * sizeof(mat[0]));
1092   for (CeedInt i = 0; i < n; i++) {
1093     for (CeedInt j = 0; j < n; j++) mat[j + n * i] = (i == j) ? 1 : 0;
1094   }
1095 
1096   // Reduce to tridiagonal
1097   for (CeedInt i = 0; i < n - 1; i++) {
1098     // Calculate Householder vector, magnitude
1099     CeedScalar sigma = 0.0;
1100 
1101     v[i] = mat_T[i + n * (i + 1)];
1102     for (CeedInt j = i + 1; j < n - 1; j++) {
1103       v[j] = mat_T[i + n * (j + 1)];
1104       sigma += v[j] * v[j];
1105     }
1106     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:n-1]
1107     const CeedScalar R_ii = -copysign(norm, v[i]);
1108 
1109     v[i] -= R_ii;
1110     // norm of v[i:m] after modification above and scaling below
1111     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
1112     //   tau = 2 / (norm*norm)
1113     tau[i] = i == n - 2 ? 2 : 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
1114     for (CeedInt j = i + 1; j < n - 1; j++) v[j] /= v[i];
1115 
1116     // Update sub and super diagonal
1117     for (CeedInt j = i + 2; j < n; j++) {
1118       mat_T[i + n * j] = 0;
1119       mat_T[j + n * i] = 0;
1120     }
1121     // Apply symmetric Householder reflector to lower right panel
1122     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1123     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), 1, n);
1124 
1125     // Save v
1126     mat_T[i + n * (i + 1)] = R_ii;
1127     mat_T[(i + 1) + n * i] = R_ii;
1128     for (CeedInt j = i + 1; j < n - 1; j++) {
1129       mat_T[i + n * (j + 1)] = v[j];
1130     }
1131   }
1132   // Backwards accumulation of Q
1133   for (CeedInt i = n - 2; i >= 0; i--) {
1134     if (tau[i] > 0.0) {
1135       v[i] = 1;
1136       for (CeedInt j = i + 1; j < n - 1; j++) {
1137         v[j]                   = mat_T[i + n * (j + 1)];
1138         mat_T[i + n * (j + 1)] = 0;
1139       }
1140       CeedHouseholderReflect(&mat[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1141     }
1142   }
1143 
1144   // Reduce sub and super diagonal
1145   CeedInt    p = 0, q = 0, itr = 0, max_itr = n * n * n * n;
1146   CeedScalar tol = CEED_EPSILON;
1147 
1148   while (itr < max_itr) {
1149     // Update p, q, size of reduced portions of diagonal
1150     p = 0;
1151     q = 0;
1152     for (CeedInt i = n - 2; i >= 0; i--) {
1153       if (fabs(mat_T[i + n * (i + 1)]) < tol) q += 1;
1154       else break;
1155     }
1156     for (CeedInt i = 0; i < n - q - 1; i++) {
1157       if (fabs(mat_T[i + n * (i + 1)]) < tol) p += 1;
1158       else break;
1159     }
1160     if (q == n - 1) break;  // Finished reducing
1161 
1162     // Reduce tridiagonal portion
1163     CeedScalar t_nn = mat_T[(n - 1 - q) + n * (n - 1 - q)], t_nnm1 = mat_T[(n - 2 - q) + n * (n - 1 - q)];
1164     CeedScalar d  = (mat_T[(n - 2 - q) + n * (n - 2 - q)] - t_nn) / 2;
1165     CeedScalar mu = t_nn - t_nnm1 * t_nnm1 / (d + copysign(sqrt(d * d + t_nnm1 * t_nnm1), d));
1166     CeedScalar x  = mat_T[p + n * p] - mu;
1167     CeedScalar z  = mat_T[p + n * (p + 1)];
1168 
1169     for (CeedInt k = p; k < n - q - 1; k++) {
1170       // Compute Givens rotation
1171       CeedScalar c = 1, s = 0;
1172 
1173       if (fabs(z) > tol) {
1174         if (fabs(z) > fabs(x)) {
1175           const CeedScalar tau = -x / z;
1176 
1177           s = 1 / sqrt(1 + tau * tau);
1178           c = s * tau;
1179         } else {
1180           const CeedScalar tau = -z / x;
1181 
1182           c = 1 / sqrt(1 + tau * tau);
1183           s = c * tau;
1184         }
1185       }
1186 
1187       // Apply Givens rotation to T
1188       CeedGivensRotation(mat_T, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1189       CeedGivensRotation(mat_T, c, s, CEED_TRANSPOSE, k, k + 1, n, n);
1190 
1191       // Apply Givens rotation to Q
1192       CeedGivensRotation(mat, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1193 
1194       // Update x, z
1195       if (k < n - q - 2) {
1196         x = mat_T[k + n * (k + 1)];
1197         z = mat_T[k + n * (k + 2)];
1198       }
1199     }
1200     itr++;
1201   }
1202 
1203   // Save eigenvalues
1204   for (CeedInt i = 0; i < n; i++) lambda[i] = mat_T[i + n * i];
1205 
1206   // Check convergence
1207   CeedCheck(itr < max_itr || q > n, ceed, CEED_ERROR_MINOR, "Symmetric QR failed to converge");
1208   return CEED_ERROR_SUCCESS;
1209 }
1210 CeedPragmaOptimizeOn
1211 
1212 /**
1213   @brief Return Simultaneous Diagonalization of two matrices.
1214 
1215   This solves the generalized eigenvalue problem `A x = lambda B x`, where `A` and `B` are symmetric and `B` is positive definite.
1216   We generate the matrix `X` and vector `Lambda` such that `X^T A X = Lambda` and `X^T B X = I`.
1217   This is equivalent to the LAPACK routine 'sygv' with `TYPE = 1`.
1218 
1219   @param[in]  ceed   `Ceed` context for error handling
1220   @param[in]  mat_A  Row-major matrix to be factorized with eigenvalues
1221   @param[in]  mat_B  Row-major matrix to be factorized to identity
1222   @param[out] mat_X  Row-major orthogonal matrix
1223   @param[out] lambda Vector of length `n` of generalized eigenvalues
1224   @param[in]  n      Number of rows/columns
1225 
1226   @return An error code: 0 - success, otherwise - failure
1227 
1228   @ref Utility
1229 **/
1230 CeedPragmaOptimizeOff
1231 int CeedSimultaneousDiagonalization(Ceed ceed, CeedScalar *mat_A, CeedScalar *mat_B, CeedScalar *mat_X, CeedScalar *lambda, CeedInt n) {
1232   CeedScalar *mat_C, *mat_G, *vec_D;
1233 
1234   CeedCall(CeedCalloc(n * n, &mat_C));
1235   CeedCall(CeedCalloc(n * n, &mat_G));
1236   CeedCall(CeedCalloc(n, &vec_D));
1237 
1238   // Compute B = G D G^T
1239   memcpy(mat_G, mat_B, n * n * sizeof(mat_B[0]));
1240   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_G, vec_D, n));
1241 
1242   // Sort eigenvalues
1243   for (CeedInt i = n - 1; i >= 0; i--) {
1244     for (CeedInt j = 0; j < i; j++) {
1245       if (fabs(vec_D[j]) > fabs(vec_D[j + 1])) {
1246         CeedScalarSwap(vec_D[j], vec_D[j + 1]);
1247         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_G[k * n + j], mat_G[k * n + j + 1]);
1248       }
1249     }
1250   }
1251 
1252   // Compute C = (G D^1/2)^-1 A (G D^1/2)^-T
1253   //           = D^-1/2 G^T A G D^-1/2
1254   // -- D = D^-1/2
1255   for (CeedInt i = 0; i < n; i++) vec_D[i] = 1. / sqrt(vec_D[i]);
1256   // -- G = G D^-1/2
1257   // -- C = D^-1/2 G^T
1258   for (CeedInt i = 0; i < n; i++) {
1259     for (CeedInt j = 0; j < n; j++) {
1260       mat_G[i * n + j] *= vec_D[j];
1261       mat_C[j * n + i] = mat_G[i * n + j];
1262     }
1263   }
1264   // -- X = (D^-1/2 G^T) A
1265   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_C, (const CeedScalar *)mat_A, mat_X, n, n, n));
1266   // -- C = (D^-1/2 G^T A) (G D^-1/2)
1267   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_X, (const CeedScalar *)mat_G, mat_C, n, n, n));
1268 
1269   // Compute Q^T C Q = lambda
1270   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_C, lambda, n));
1271 
1272   // Sort eigenvalues
1273   for (CeedInt i = n - 1; i >= 0; i--) {
1274     for (CeedInt j = 0; j < i; j++) {
1275       if (fabs(lambda[j]) > fabs(lambda[j + 1])) {
1276         CeedScalarSwap(lambda[j], lambda[j + 1]);
1277         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_C[k * n + j], mat_C[k * n + j + 1]);
1278       }
1279     }
1280   }
1281 
1282   // Set X = (G D^1/2)^-T Q
1283   //       = G D^-1/2 Q
1284   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_G, (const CeedScalar *)mat_C, mat_X, n, n, n));
1285 
1286   // Cleanup
1287   CeedCall(CeedFree(&mat_C));
1288   CeedCall(CeedFree(&mat_G));
1289   CeedCall(CeedFree(&vec_D));
1290   return CEED_ERROR_SUCCESS;
1291 }
1292 CeedPragmaOptimizeOn
1293 
1294 /// @}
1295 
1296 /// ----------------------------------------------------------------------------
1297 /// CeedBasis Public API
1298 /// ----------------------------------------------------------------------------
1299 /// @addtogroup CeedBasisUser
1300 /// @{
1301 
1302 /**
1303   @brief Create a tensor-product basis for \f$H^1\f$ discretizations
1304 
1305   @param[in]  ceed        `Ceed` object used to create the `CeedBasis`
1306   @param[in]  dim         Topological dimension
1307   @param[in]  num_comp    Number of field components (1 for scalar fields)
1308   @param[in]  P_1d        Number of nodes in one dimension
1309   @param[in]  Q_1d        Number of quadrature points in one dimension
1310   @param[in]  interp_1d   Row-major (`Q_1d * P_1d`) matrix expressing the values of nodal basis functions at quadrature points
1311   @param[in]  grad_1d     Row-major (`Q_1d * P_1d`) matrix expressing derivatives of nodal basis functions at quadrature points
1312   @param[in]  q_ref_1d    Array of length `Q_1d` holding the locations of quadrature points on the 1D reference element `[-1, 1]`
1313   @param[in]  q_weight_1d Array of length `Q_1d` holding the quadrature weights on the reference element
1314   @param[out] basis       Address of the variable where the newly created `CeedBasis` will be stored
1315 
1316   @return An error code: 0 - success, otherwise - failure
1317 
1318   @ref User
1319 **/
1320 int CeedBasisCreateTensorH1(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P_1d, CeedInt Q_1d, const CeedScalar *interp_1d,
1321                             const CeedScalar *grad_1d, const CeedScalar *q_ref_1d, const CeedScalar *q_weight_1d, CeedBasis *basis) {
1322   if (!ceed->BasisCreateTensorH1) {
1323     Ceed delegate;
1324 
1325     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1326     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateTensorH1");
1327     CeedCall(CeedBasisCreateTensorH1(delegate, dim, num_comp, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1328     return CEED_ERROR_SUCCESS;
1329   }
1330 
1331   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1332   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1333   CeedCheck(P_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1334   CeedCheck(Q_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1335 
1336   CeedElemTopology topo = dim == 1 ? CEED_TOPOLOGY_LINE : dim == 2 ? CEED_TOPOLOGY_QUAD : CEED_TOPOLOGY_HEX;
1337 
1338   CeedCall(CeedCalloc(1, basis));
1339   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1340   (*basis)->ref_count       = 1;
1341   (*basis)->is_tensor_basis = true;
1342   (*basis)->dim             = dim;
1343   (*basis)->topo            = topo;
1344   (*basis)->num_comp        = num_comp;
1345   (*basis)->P_1d            = P_1d;
1346   (*basis)->Q_1d            = Q_1d;
1347   (*basis)->P               = CeedIntPow(P_1d, dim);
1348   (*basis)->Q               = CeedIntPow(Q_1d, dim);
1349   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1350   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_ref_1d));
1351   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_weight_1d));
1352   if (q_ref_1d) memcpy((*basis)->q_ref_1d, q_ref_1d, Q_1d * sizeof(q_ref_1d[0]));
1353   if (q_weight_1d) memcpy((*basis)->q_weight_1d, q_weight_1d, Q_1d * sizeof(q_weight_1d[0]));
1354   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->interp_1d));
1355   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->grad_1d));
1356   if (interp_1d) memcpy((*basis)->interp_1d, interp_1d, Q_1d * P_1d * sizeof(interp_1d[0]));
1357   if (grad_1d) memcpy((*basis)->grad_1d, grad_1d, Q_1d * P_1d * sizeof(grad_1d[0]));
1358   CeedCall(ceed->BasisCreateTensorH1(dim, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, *basis));
1359   return CEED_ERROR_SUCCESS;
1360 }
1361 
1362 /**
1363   @brief Create a tensor-product \f$H^1\f$ Lagrange basis
1364 
1365   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1366   @param[in]  dim       Topological dimension of element
1367   @param[in]  num_comp  Number of field components (1 for scalar fields)
1368   @param[in]  P         Number of Gauss-Lobatto nodes in one dimension.
1369                           The polynomial degree of the resulting `Q_k` element is `k = P - 1`.
1370   @param[in]  Q         Number of quadrature points in one dimension.
1371   @param[in]  quad_mode Distribution of the `Q` quadrature points (affects order of accuracy for the quadrature)
1372   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1373 
1374   @return An error code: 0 - success, otherwise - failure
1375 
1376   @ref User
1377 **/
1378 int CeedBasisCreateTensorH1Lagrange(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P, CeedInt Q, CeedQuadMode quad_mode, CeedBasis *basis) {
1379   // Allocate
1380   int        ierr = CEED_ERROR_SUCCESS;
1381   CeedScalar c1, c2, c3, c4, dx, *nodes, *interp_1d, *grad_1d, *q_ref_1d, *q_weight_1d;
1382 
1383   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1384   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1385   CeedCheck(P > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1386   CeedCheck(Q > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1387 
1388   // Get Nodes and Weights
1389   CeedCall(CeedCalloc(P * Q, &interp_1d));
1390   CeedCall(CeedCalloc(P * Q, &grad_1d));
1391   CeedCall(CeedCalloc(P, &nodes));
1392   CeedCall(CeedCalloc(Q, &q_ref_1d));
1393   CeedCall(CeedCalloc(Q, &q_weight_1d));
1394   if (CeedLobattoQuadrature(P, nodes, NULL) != CEED_ERROR_SUCCESS) goto cleanup;
1395   switch (quad_mode) {
1396     case CEED_GAUSS:
1397       ierr = CeedGaussQuadrature(Q, q_ref_1d, q_weight_1d);
1398       break;
1399     case CEED_GAUSS_LOBATTO:
1400       ierr = CeedLobattoQuadrature(Q, q_ref_1d, q_weight_1d);
1401       break;
1402   }
1403   if (ierr != CEED_ERROR_SUCCESS) goto cleanup;
1404 
1405   // Build B, D matrix
1406   // Fornberg, 1998
1407   for (CeedInt i = 0; i < Q; i++) {
1408     c1                   = 1.0;
1409     c3                   = nodes[0] - q_ref_1d[i];
1410     interp_1d[i * P + 0] = 1.0;
1411     for (CeedInt j = 1; j < P; j++) {
1412       c2 = 1.0;
1413       c4 = c3;
1414       c3 = nodes[j] - q_ref_1d[i];
1415       for (CeedInt k = 0; k < j; k++) {
1416         dx = nodes[j] - nodes[k];
1417         c2 *= dx;
1418         if (k == j - 1) {
1419           grad_1d[i * P + j]   = c1 * (interp_1d[i * P + k] - c4 * grad_1d[i * P + k]) / c2;
1420           interp_1d[i * P + j] = -c1 * c4 * interp_1d[i * P + k] / c2;
1421         }
1422         grad_1d[i * P + k]   = (c3 * grad_1d[i * P + k] - interp_1d[i * P + k]) / dx;
1423         interp_1d[i * P + k] = c3 * interp_1d[i * P + k] / dx;
1424       }
1425       c1 = c2;
1426     }
1427   }
1428   // Pass to CeedBasisCreateTensorH1
1429   CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P, Q, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1430 cleanup:
1431   CeedCall(CeedFree(&interp_1d));
1432   CeedCall(CeedFree(&grad_1d));
1433   CeedCall(CeedFree(&nodes));
1434   CeedCall(CeedFree(&q_ref_1d));
1435   CeedCall(CeedFree(&q_weight_1d));
1436   return CEED_ERROR_SUCCESS;
1437 }
1438 
1439 /**
1440   @brief Create a non tensor-product basis for \f$H^1\f$ discretizations
1441 
1442   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1443   @param[in]  topo      Topology of element, e.g. hypercube, simplex, etc
1444   @param[in]  num_comp  Number of field components (1 for scalar fields)
1445   @param[in]  num_nodes Total number of nodes
1446   @param[in]  num_qpts  Total number of quadrature points
1447   @param[in]  interp    Row-major (`num_qpts * num_nodes`) matrix expressing the values of nodal basis functions at quadrature points
1448   @param[in]  grad      Row-major (`dim * num_qpts * num_nodes`) matrix expressing derivatives of nodal basis functions at quadrature points
1449   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1450   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1451   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1452 
1453   @return An error code: 0 - success, otherwise - failure
1454 
1455   @ref User
1456 **/
1457 int CeedBasisCreateH1(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1458                       const CeedScalar *grad, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1459   CeedInt P = num_nodes, Q = num_qpts, dim = 0;
1460 
1461   if (!ceed->BasisCreateH1) {
1462     Ceed delegate;
1463 
1464     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1465     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateH1");
1466     CeedCall(CeedBasisCreateH1(delegate, topo, num_comp, num_nodes, num_qpts, interp, grad, q_ref, q_weight, basis));
1467     return CEED_ERROR_SUCCESS;
1468   }
1469 
1470   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1471   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1472   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1473 
1474   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1475 
1476   CeedCall(CeedCalloc(1, basis));
1477   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1478   (*basis)->ref_count       = 1;
1479   (*basis)->is_tensor_basis = false;
1480   (*basis)->dim             = dim;
1481   (*basis)->topo            = topo;
1482   (*basis)->num_comp        = num_comp;
1483   (*basis)->P               = P;
1484   (*basis)->Q               = Q;
1485   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1486   CeedCall(CeedCalloc(Q * dim, &(*basis)->q_ref_1d));
1487   CeedCall(CeedCalloc(Q, &(*basis)->q_weight_1d));
1488   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1489   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1490   CeedCall(CeedCalloc(Q * P, &(*basis)->interp));
1491   CeedCall(CeedCalloc(dim * Q * P, &(*basis)->grad));
1492   if (interp) memcpy((*basis)->interp, interp, Q * P * sizeof(interp[0]));
1493   if (grad) memcpy((*basis)->grad, grad, dim * Q * P * sizeof(grad[0]));
1494   CeedCall(ceed->BasisCreateH1(topo, dim, P, Q, interp, grad, q_ref, q_weight, *basis));
1495   return CEED_ERROR_SUCCESS;
1496 }
1497 
1498 /**
1499   @brief Create a non tensor-product basis for \f$H(\mathrm{div})\f$ discretizations
1500 
1501   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1502   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1503   @param[in]  num_comp  Number of components (usually 1 for vectors in H(div) bases)
1504   @param[in]  num_nodes Total number of nodes (DoFs per element)
1505   @param[in]  num_qpts  Total number of quadrature points
1506   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1507   @param[in]  div       Row-major (`num_qpts * num_nodes`) matrix expressing divergence of basis functions at quadrature points
1508   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1509   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1510   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1511 
1512   @return An error code: 0 - success, otherwise - failure
1513 
1514   @ref User
1515 **/
1516 int CeedBasisCreateHdiv(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1517                         const CeedScalar *div, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1518   CeedInt Q = num_qpts, P = num_nodes, dim = 0;
1519 
1520   if (!ceed->BasisCreateHdiv) {
1521     Ceed delegate;
1522 
1523     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1524     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHdiv");
1525     CeedCall(CeedBasisCreateHdiv(delegate, topo, num_comp, num_nodes, num_qpts, interp, div, q_ref, q_weight, basis));
1526     return CEED_ERROR_SUCCESS;
1527   }
1528 
1529   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1530   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1531   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1532 
1533   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1534 
1535   CeedCall(CeedCalloc(1, basis));
1536   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1537   (*basis)->ref_count       = 1;
1538   (*basis)->is_tensor_basis = false;
1539   (*basis)->dim             = dim;
1540   (*basis)->topo            = topo;
1541   (*basis)->num_comp        = num_comp;
1542   (*basis)->P               = P;
1543   (*basis)->Q               = Q;
1544   (*basis)->fe_space        = CEED_FE_SPACE_HDIV;
1545   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1546   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1547   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1548   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1549   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1550   CeedCall(CeedMalloc(Q * P, &(*basis)->div));
1551   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1552   if (div) memcpy((*basis)->div, div, Q * P * sizeof(div[0]));
1553   CeedCall(ceed->BasisCreateHdiv(topo, dim, P, Q, interp, div, q_ref, q_weight, *basis));
1554   return CEED_ERROR_SUCCESS;
1555 }
1556 
1557 /**
1558   @brief Create a non tensor-product basis for \f$H(\mathrm{curl})\f$ discretizations
1559 
1560   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1561   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1562   @param[in]  num_comp  Number of components (usually 1 for vectors in \f$H(\mathrm{curl})\f$ bases)
1563   @param[in]  num_nodes Total number of nodes (DoFs per element)
1564   @param[in]  num_qpts  Total number of quadrature points
1565   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1566   @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
1567   @param[in]  q_ref     Array of length `num_qpts * dim` holding the locations of quadrature points on the reference element
1568   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1569   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1570 
1571   @return An error code: 0 - success, otherwise - failure
1572 
1573   @ref User
1574 **/
1575 int CeedBasisCreateHcurl(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1576                          const CeedScalar *curl, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1577   CeedInt Q = num_qpts, P = num_nodes, dim = 0, curl_comp = 0;
1578 
1579   if (!ceed->BasisCreateHcurl) {
1580     Ceed delegate;
1581 
1582     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1583     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHcurl");
1584     CeedCall(CeedBasisCreateHcurl(delegate, topo, num_comp, num_nodes, num_qpts, interp, curl, q_ref, q_weight, basis));
1585     return CEED_ERROR_SUCCESS;
1586   }
1587 
1588   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1589   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1590   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1591 
1592   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1593   curl_comp = (dim < 3) ? 1 : dim;
1594 
1595   CeedCall(CeedCalloc(1, basis));
1596   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1597   (*basis)->ref_count       = 1;
1598   (*basis)->is_tensor_basis = false;
1599   (*basis)->dim             = dim;
1600   (*basis)->topo            = topo;
1601   (*basis)->num_comp        = num_comp;
1602   (*basis)->P               = P;
1603   (*basis)->Q               = Q;
1604   (*basis)->fe_space        = CEED_FE_SPACE_HCURL;
1605   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1606   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1607   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1608   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1609   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1610   CeedCall(CeedMalloc(curl_comp * Q * P, &(*basis)->curl));
1611   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1612   if (curl) memcpy((*basis)->curl, curl, curl_comp * Q * P * sizeof(curl[0]));
1613   CeedCall(ceed->BasisCreateHcurl(topo, dim, P, Q, interp, curl, q_ref, q_weight, *basis));
1614   return CEED_ERROR_SUCCESS;
1615 }
1616 
1617 /**
1618   @brief Create a `CeedBasis` for projection from the nodes of `basis_from` to the nodes of `basis_to`.
1619 
1620   Only @ref CEED_EVAL_INTERP will be valid for the new basis, `basis_project`.
1621   For \f$H^1\f$ spaces, @ref CEED_EVAL_GRAD will also be valid.
1622   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
1623   The gradient (for the \f$H^1\f$ case) is given by `grad_project = interp_to^+ * grad_from`.
1624 
1625   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
1626 
1627   Note: `basis_project` will have the same number of components as `basis_from`, regardless of the number of components that `basis_to` has.
1628         If `basis_from` has 3 components and `basis_to` has 5 components, then `basis_project` will have 3 components.
1629 
1630   Note: If either `basis_from` or `basis_to` are non-tensor, then `basis_project` will also be non-tensor
1631 
1632   @param[in]  basis_from    `CeedBasis` to prolong from
1633   @param[in]  basis_to      `CeedBasis` to prolong to
1634   @param[out] basis_project Address of the variable where the newly created `CeedBasis` will be stored
1635 
1636   @return An error code: 0 - success, otherwise - failure
1637 
1638   @ref User
1639 **/
1640 int CeedBasisCreateProjection(CeedBasis basis_from, CeedBasis basis_to, CeedBasis *basis_project) {
1641   Ceed        ceed;
1642   bool        create_tensor;
1643   CeedInt     dim, num_comp;
1644   CeedScalar *interp_project, *grad_project;
1645 
1646   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
1647 
1648   // Create projection matrix
1649   CeedCall(CeedBasisCreateProjectionMatrices(basis_from, basis_to, &interp_project, &grad_project));
1650 
1651   // Build basis
1652   {
1653     bool is_tensor_to, is_tensor_from;
1654 
1655     CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
1656     CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
1657     create_tensor = is_tensor_from && is_tensor_to;
1658   }
1659   CeedCall(CeedBasisGetDimension(basis_to, &dim));
1660   CeedCall(CeedBasisGetNumComponents(basis_from, &num_comp));
1661   if (create_tensor) {
1662     CeedInt P_1d_to, P_1d_from;
1663 
1664     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_1d_from));
1665     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_1d_to));
1666     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d_from, P_1d_to, interp_project, grad_project, NULL, NULL, basis_project));
1667   } else {
1668     // Even if basis_to and basis_from are not H1, the resulting basis is H1 for interpolation to work
1669     CeedInt          num_nodes_to, num_nodes_from;
1670     CeedElemTopology topo;
1671 
1672     CeedCall(CeedBasisGetTopology(basis_from, &topo));
1673     CeedCall(CeedBasisGetNumNodes(basis_from, &num_nodes_from));
1674     CeedCall(CeedBasisGetNumNodes(basis_to, &num_nodes_to));
1675     CeedCall(CeedBasisCreateH1(ceed, topo, num_comp, num_nodes_from, num_nodes_to, interp_project, grad_project, NULL, NULL, basis_project));
1676   }
1677 
1678   // Cleanup
1679   CeedCall(CeedFree(&interp_project));
1680   CeedCall(CeedFree(&grad_project));
1681   return CEED_ERROR_SUCCESS;
1682 }
1683 
1684 /**
1685   @brief Copy the pointer to a `CeedBasis`.
1686 
1687   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`.
1688         This `CeedBasis` will be destroyed if `*basis_copy` is the only reference to this `CeedBasis`.
1689 
1690   @param[in]     basis      `CeedBasis` to copy reference to
1691   @param[in,out] basis_copy Variable to store copied reference
1692 
1693   @return An error code: 0 - success, otherwise - failure
1694 
1695   @ref User
1696 **/
1697 int CeedBasisReferenceCopy(CeedBasis basis, CeedBasis *basis_copy) {
1698   if (basis != CEED_BASIS_NONE) CeedCall(CeedBasisReference(basis));
1699   CeedCall(CeedBasisDestroy(basis_copy));
1700   *basis_copy = basis;
1701   return CEED_ERROR_SUCCESS;
1702 }
1703 
1704 /**
1705   @brief View a `CeedBasis`
1706 
1707   @param[in] basis  `CeedBasis` to view
1708   @param[in] stream Stream to view to, e.g., `stdout`
1709 
1710   @return An error code: 0 - success, otherwise - failure
1711 
1712   @ref User
1713 **/
1714 int CeedBasisView(CeedBasis basis, FILE *stream) {
1715   bool             is_tensor_basis;
1716   CeedElemTopology topo;
1717   CeedFESpace      fe_space;
1718 
1719   // Basis data
1720   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
1721   CeedCall(CeedBasisGetTopology(basis, &topo));
1722   CeedCall(CeedBasisGetFESpace(basis, &fe_space));
1723 
1724   // Print FE space and element topology of the basis
1725   fprintf(stream, "CeedBasis in a %s on a %s element\n", CeedFESpaces[fe_space], CeedElemTopologies[topo]);
1726   if (is_tensor_basis) {
1727     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P_1d, basis->Q_1d);
1728   } else {
1729     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P, basis->Q);
1730   }
1731   fprintf(stream, "  dimension: %" CeedInt_FMT "\n  field components: %" CeedInt_FMT "\n", basis->dim, basis->num_comp);
1732   // Print quadrature data, interpolation/gradient/divergence/curl of the basis
1733   if (is_tensor_basis) {  // tensor basis
1734     CeedInt           P_1d, Q_1d;
1735     const CeedScalar *q_ref_1d, *q_weight_1d, *interp_1d, *grad_1d;
1736 
1737     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
1738     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
1739     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
1740     CeedCall(CeedBasisGetQWeights(basis, &q_weight_1d));
1741     CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
1742     CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
1743 
1744     CeedCall(CeedScalarView("qref1d", "\t% 12.8f", 1, Q_1d, q_ref_1d, stream));
1745     CeedCall(CeedScalarView("qweight1d", "\t% 12.8f", 1, Q_1d, q_weight_1d, stream));
1746     CeedCall(CeedScalarView("interp1d", "\t% 12.8f", Q_1d, P_1d, interp_1d, stream));
1747     CeedCall(CeedScalarView("grad1d", "\t% 12.8f", Q_1d, P_1d, grad_1d, stream));
1748   } else {  // non-tensor basis
1749     CeedInt           P, Q, dim, q_comp;
1750     const CeedScalar *q_ref, *q_weight, *interp, *grad, *div, *curl;
1751 
1752     CeedCall(CeedBasisGetNumNodes(basis, &P));
1753     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &Q));
1754     CeedCall(CeedBasisGetDimension(basis, &dim));
1755     CeedCall(CeedBasisGetQRef(basis, &q_ref));
1756     CeedCall(CeedBasisGetQWeights(basis, &q_weight));
1757     CeedCall(CeedBasisGetInterp(basis, &interp));
1758     CeedCall(CeedBasisGetGrad(basis, &grad));
1759     CeedCall(CeedBasisGetDiv(basis, &div));
1760     CeedCall(CeedBasisGetCurl(basis, &curl));
1761 
1762     CeedCall(CeedScalarView("qref", "\t% 12.8f", 1, Q * dim, q_ref, stream));
1763     CeedCall(CeedScalarView("qweight", "\t% 12.8f", 1, Q, q_weight, stream));
1764     CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_INTERP, &q_comp));
1765     CeedCall(CeedScalarView("interp", "\t% 12.8f", q_comp * Q, P, interp, stream));
1766     if (grad) {
1767       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_GRAD, &q_comp));
1768       CeedCall(CeedScalarView("grad", "\t% 12.8f", q_comp * Q, P, grad, stream));
1769     }
1770     if (div) {
1771       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_DIV, &q_comp));
1772       CeedCall(CeedScalarView("div", "\t% 12.8f", q_comp * Q, P, div, stream));
1773     }
1774     if (curl) {
1775       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_CURL, &q_comp));
1776       CeedCall(CeedScalarView("curl", "\t% 12.8f", q_comp * Q, P, curl, stream));
1777     }
1778   }
1779   return CEED_ERROR_SUCCESS;
1780 }
1781 
1782 /**
1783   @brief Check input vector dimensions for CeedBasisApply[Add]
1784 
1785   @param[in]  basis     `CeedBasis` to evaluate
1786   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1787                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1788   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1789                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1790   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1791                           @ref CEED_EVAL_INTERP to use interpolated values,
1792                           @ref CEED_EVAL_GRAD to use gradients,
1793                           @ref CEED_EVAL_DIV to use divergence,
1794                           @ref CEED_EVAL_CURL to use curl,
1795                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1796   @param[in]  u         Input `CeedVector`
1797   @param[out] v         Output `CeedVector`
1798 
1799   @return An error code: 0 - success, otherwise - failure
1800 
1801   @ref Developer
1802 **/
1803 static int CeedBasisApplyCheckDims(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1804   CeedInt  dim, num_comp, q_comp, num_nodes, num_qpts;
1805   CeedSize u_length = 0, v_length;
1806   Ceed     ceed;
1807 
1808   CeedCall(CeedBasisGetCeed(basis, &ceed));
1809   CeedCall(CeedBasisGetDimension(basis, &dim));
1810   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1811   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
1812   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1813   CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
1814   CeedCall(CeedVectorGetLength(v, &v_length));
1815   if (u) CeedCall(CeedVectorGetLength(u, &u_length));
1816 
1817   // Check vector lengths to prevent out of bounds issues
1818   bool has_good_dims = true;
1819   switch (eval_mode) {
1820     case CEED_EVAL_NONE:
1821     case CEED_EVAL_INTERP:
1822     case CEED_EVAL_GRAD:
1823     case CEED_EVAL_DIV:
1824     case CEED_EVAL_CURL:
1825       has_good_dims =
1826           ((t_mode == CEED_TRANSPOSE && u_length >= num_elem * num_comp * num_qpts * q_comp && v_length >= num_elem * num_comp * num_nodes) ||
1827            (t_mode == CEED_NOTRANSPOSE && v_length >= num_elem * num_qpts * num_comp * q_comp && u_length >= num_elem * num_comp * num_nodes));
1828       break;
1829     case CEED_EVAL_WEIGHT:
1830       has_good_dims = v_length >= num_elem * num_qpts;
1831       break;
1832   }
1833   CeedCheck(has_good_dims, ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
1834   return CEED_ERROR_SUCCESS;
1835 }
1836 
1837 /**
1838   @brief Apply basis evaluation from nodes to quadrature points or vice versa
1839 
1840   @param[in]  basis     `CeedBasis` to evaluate
1841   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1842                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1843   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1844                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1845   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1846                           @ref CEED_EVAL_INTERP to use interpolated values,
1847                           @ref CEED_EVAL_GRAD to use gradients,
1848                           @ref CEED_EVAL_DIV to use divergence,
1849                           @ref CEED_EVAL_CURL to use curl,
1850                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1851   @param[in]  u         Input `CeedVector`
1852   @param[out] v         Output `CeedVector`
1853 
1854   @return An error code: 0 - success, otherwise - failure
1855 
1856   @ref User
1857 **/
1858 int CeedBasisApply(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1859   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
1860   CeedCheck(basis->Apply, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not support CeedBasisApply");
1861   CeedCall(basis->Apply(basis, num_elem, t_mode, eval_mode, u, v));
1862   return CEED_ERROR_SUCCESS;
1863 }
1864 
1865 /**
1866   @brief Apply basis evaluation from quadrature points to nodes and sum into target vector
1867 
1868   @param[in]  basis     `CeedBasis` to evaluate
1869   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1870                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1871   @param[in]  t_mode    @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes;
1872                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAdd()`
1873   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1874                           @ref CEED_EVAL_INTERP to use interpolated values,
1875                           @ref CEED_EVAL_GRAD to use gradients,
1876                           @ref CEED_EVAL_DIV to use divergence,
1877                           @ref CEED_EVAL_CURL to use curl,
1878                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1879   @param[in]  u         Input `CeedVector`
1880   @param[out] v         Output `CeedVector` to sum into
1881 
1882   @return An error code: 0 - success, otherwise - failure
1883 
1884   @ref User
1885 **/
1886 int CeedBasisApplyAdd(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1887   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAdd only supports CEED_TRANSPOSE");
1888   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
1889   CeedCheck(basis->ApplyAdd, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not implement CeedBasisApplyAdd");
1890   CeedCall(basis->ApplyAdd(basis, num_elem, t_mode, eval_mode, u, v));
1891   return CEED_ERROR_SUCCESS;
1892 }
1893 
1894 /**
1895   @brief Apply basis evaluation from nodes to arbitrary points
1896 
1897   @param[in]  basis      `CeedBasis` to evaluate
1898   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
1899                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1900   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
1901   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1902                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
1903   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
1904                            @ref CEED_EVAL_GRAD to use gradients,
1905                            @ref CEED_EVAL_WEIGHT to use quadrature weights
1906   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
1907   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
1908   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
1909 
1910   @return An error code: 0 - success, otherwise - failure
1911 
1912   @ref User
1913 **/
1914 int CeedBasisApplyAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
1915                            CeedVector x_ref, CeedVector u, CeedVector v) {
1916   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1917   if (basis->ApplyAtPoints) {
1918     CeedCall(basis->ApplyAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1919   } else {
1920     CeedCall(CeedBasisApplyAtPoints_Core(basis, false, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1921   }
1922   return CEED_ERROR_SUCCESS;
1923 }
1924 
1925 /**
1926   @brief Apply basis evaluation from nodes to arbitrary points and sum into target vector
1927 
1928   @param[in]  basis      `CeedBasis` to evaluate
1929   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
1930                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1931   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
1932   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1933                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAddAtPoints()`
1934   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
1935                            @ref CEED_EVAL_GRAD to use gradients,
1936                            @ref CEED_EVAL_WEIGHT to use quadrature weights
1937   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
1938   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
1939   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
1940 
1941   @return An error code: 0 - success, otherwise - failure
1942 
1943   @ref User
1944 **/
1945 int CeedBasisApplyAddAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
1946                               CeedVector x_ref, CeedVector u, CeedVector v) {
1947   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAddAtPoints only supports CEED_TRANSPOSE");
1948   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1949   if (basis->ApplyAddAtPoints) {
1950     CeedCall(basis->ApplyAddAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1951   } else {
1952     CeedCall(CeedBasisApplyAtPoints_Core(basis, true, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1953   }
1954   return CEED_ERROR_SUCCESS;
1955 }
1956 
1957 /**
1958   @brief Get the `Ceed` associated with a `CeedBasis`
1959 
1960   @param[in]  basis `CeedBasis`
1961   @param[out] ceed  Variable to store `Ceed`
1962 
1963   @return An error code: 0 - success, otherwise - failure
1964 
1965   @ref Advanced
1966 **/
1967 int CeedBasisGetCeed(CeedBasis basis, Ceed *ceed) {
1968   *ceed = CeedBasisReturnCeed(basis);
1969   return CEED_ERROR_SUCCESS;
1970 }
1971 
1972 /**
1973   @brief Return the `Ceed` associated with a `CeedBasis`
1974 
1975   @param[in]  basis `CeedBasis`
1976 
1977   @return `Ceed` associated with the `basis`
1978 
1979   @ref Advanced
1980 **/
1981 Ceed CeedBasisReturnCeed(CeedBasis basis) { return basis->ceed; }
1982 
1983 /**
1984   @brief Get dimension for given `CeedBasis`
1985 
1986   @param[in]  basis `CeedBasis`
1987   @param[out] dim   Variable to store dimension of basis
1988 
1989   @return An error code: 0 - success, otherwise - failure
1990 
1991   @ref Advanced
1992 **/
1993 int CeedBasisGetDimension(CeedBasis basis, CeedInt *dim) {
1994   *dim = basis->dim;
1995   return CEED_ERROR_SUCCESS;
1996 }
1997 
1998 /**
1999   @brief Get topology for given `CeedBasis`
2000 
2001   @param[in]  basis `CeedBasis`
2002   @param[out] topo  Variable to store topology of basis
2003 
2004   @return An error code: 0 - success, otherwise - failure
2005 
2006   @ref Advanced
2007 **/
2008 int CeedBasisGetTopology(CeedBasis basis, CeedElemTopology *topo) {
2009   *topo = basis->topo;
2010   return CEED_ERROR_SUCCESS;
2011 }
2012 
2013 /**
2014   @brief Get number of components for given `CeedBasis`
2015 
2016   @param[in]  basis    `CeedBasis`
2017   @param[out] num_comp Variable to store number of components
2018 
2019   @return An error code: 0 - success, otherwise - failure
2020 
2021   @ref Advanced
2022 **/
2023 int CeedBasisGetNumComponents(CeedBasis basis, CeedInt *num_comp) {
2024   *num_comp = basis->num_comp;
2025   return CEED_ERROR_SUCCESS;
2026 }
2027 
2028 /**
2029   @brief Get total number of nodes (in `dim` dimensions) of a `CeedBasis`
2030 
2031   @param[in]  basis `CeedBasis`
2032   @param[out] P     Variable to store number of nodes
2033 
2034   @return An error code: 0 - success, otherwise - failure
2035 
2036   @ref Utility
2037 **/
2038 int CeedBasisGetNumNodes(CeedBasis basis, CeedInt *P) {
2039   *P = basis->P;
2040   return CEED_ERROR_SUCCESS;
2041 }
2042 
2043 /**
2044   @brief Get total number of nodes (in 1 dimension) of a `CeedBasis`
2045 
2046   @param[in]  basis `CeedBasis`
2047   @param[out] P_1d  Variable to store number of nodes
2048 
2049   @return An error code: 0 - success, otherwise - failure
2050 
2051   @ref Advanced
2052 **/
2053 int CeedBasisGetNumNodes1D(CeedBasis basis, CeedInt *P_1d) {
2054   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply P_1d for non-tensor CeedBasis");
2055   *P_1d = basis->P_1d;
2056   return CEED_ERROR_SUCCESS;
2057 }
2058 
2059 /**
2060   @brief Get total number of quadrature points (in `dim` dimensions) of a `CeedBasis`
2061 
2062   @param[in]  basis `CeedBasis`
2063   @param[out] Q     Variable to store number of quadrature points
2064 
2065   @return An error code: 0 - success, otherwise - failure
2066 
2067   @ref Utility
2068 **/
2069 int CeedBasisGetNumQuadraturePoints(CeedBasis basis, CeedInt *Q) {
2070   *Q = basis->Q;
2071   return CEED_ERROR_SUCCESS;
2072 }
2073 
2074 /**
2075   @brief Get total number of quadrature points (in 1 dimension) of a `CeedBasis`
2076 
2077   @param[in]  basis `CeedBasis`
2078   @param[out] Q_1d  Variable to store number of quadrature points
2079 
2080   @return An error code: 0 - success, otherwise - failure
2081 
2082   @ref Advanced
2083 **/
2084 int CeedBasisGetNumQuadraturePoints1D(CeedBasis basis, CeedInt *Q_1d) {
2085   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply Q_1d for non-tensor CeedBasis");
2086   *Q_1d = basis->Q_1d;
2087   return CEED_ERROR_SUCCESS;
2088 }
2089 
2090 /**
2091   @brief Get reference coordinates of quadrature points (in `dim` dimensions) of a `CeedBasis`
2092 
2093   @param[in]  basis `CeedBasis`
2094   @param[out] q_ref Variable to store reference coordinates of quadrature points
2095 
2096   @return An error code: 0 - success, otherwise - failure
2097 
2098   @ref Advanced
2099 **/
2100 int CeedBasisGetQRef(CeedBasis basis, const CeedScalar **q_ref) {
2101   *q_ref = basis->q_ref_1d;
2102   return CEED_ERROR_SUCCESS;
2103 }
2104 
2105 /**
2106   @brief Get quadrature weights of quadrature points (in `dim` dimensions) of a `CeedBasis`
2107 
2108   @param[in]  basis    `CeedBasis`
2109   @param[out] q_weight Variable to store quadrature weights
2110 
2111   @return An error code: 0 - success, otherwise - failure
2112 
2113   @ref Advanced
2114 **/
2115 int CeedBasisGetQWeights(CeedBasis basis, const CeedScalar **q_weight) {
2116   *q_weight = basis->q_weight_1d;
2117   return CEED_ERROR_SUCCESS;
2118 }
2119 
2120 /**
2121   @brief Get interpolation matrix of a `CeedBasis`
2122 
2123   @param[in]  basis  `CeedBasis`
2124   @param[out] interp Variable to store interpolation matrix
2125 
2126   @return An error code: 0 - success, otherwise - failure
2127 
2128   @ref Advanced
2129 **/
2130 int CeedBasisGetInterp(CeedBasis basis, const CeedScalar **interp) {
2131   if (!basis->interp && basis->is_tensor_basis) {
2132     // Allocate
2133     CeedCall(CeedMalloc(basis->Q * basis->P, &basis->interp));
2134 
2135     // Initialize
2136     for (CeedInt i = 0; i < basis->Q * basis->P; i++) basis->interp[i] = 1.0;
2137 
2138     // Calculate
2139     for (CeedInt d = 0; d < basis->dim; d++) {
2140       for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2141         for (CeedInt node = 0; node < basis->P; node++) {
2142           CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2143           CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2144 
2145           basis->interp[qpt * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2146         }
2147       }
2148     }
2149   }
2150   *interp = basis->interp;
2151   return CEED_ERROR_SUCCESS;
2152 }
2153 
2154 /**
2155   @brief Get 1D interpolation matrix of a tensor product `CeedBasis`
2156 
2157   @param[in]  basis     `CeedBasis`
2158   @param[out] interp_1d Variable to store interpolation matrix
2159 
2160   @return An error code: 0 - success, otherwise - failure
2161 
2162   @ref Backend
2163 **/
2164 int CeedBasisGetInterp1D(CeedBasis basis, const CeedScalar **interp_1d) {
2165   bool is_tensor_basis;
2166 
2167   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2168   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2169   *interp_1d = basis->interp_1d;
2170   return CEED_ERROR_SUCCESS;
2171 }
2172 
2173 /**
2174   @brief Get gradient matrix of a `CeedBasis`
2175 
2176   @param[in]  basis `CeedBasis`
2177   @param[out] grad  Variable to store gradient matrix
2178 
2179   @return An error code: 0 - success, otherwise - failure
2180 
2181   @ref Advanced
2182 **/
2183 int CeedBasisGetGrad(CeedBasis basis, const CeedScalar **grad) {
2184   if (!basis->grad && basis->is_tensor_basis) {
2185     // Allocate
2186     CeedCall(CeedMalloc(basis->dim * basis->Q * basis->P, &basis->grad));
2187 
2188     // Initialize
2189     for (CeedInt i = 0; i < basis->dim * basis->Q * basis->P; i++) basis->grad[i] = 1.0;
2190 
2191     // Calculate
2192     for (CeedInt d = 0; d < basis->dim; d++) {
2193       for (CeedInt i = 0; i < basis->dim; i++) {
2194         for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2195           for (CeedInt node = 0; node < basis->P; node++) {
2196             CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2197             CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2198 
2199             if (i == d) basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->grad_1d[q * basis->P_1d + p];
2200             else basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2201           }
2202         }
2203       }
2204     }
2205   }
2206   *grad = basis->grad;
2207   return CEED_ERROR_SUCCESS;
2208 }
2209 
2210 /**
2211   @brief Get 1D gradient matrix of a tensor product `CeedBasis`
2212 
2213   @param[in]  basis   `CeedBasis`
2214   @param[out] grad_1d Variable to store gradient matrix
2215 
2216   @return An error code: 0 - success, otherwise - failure
2217 
2218   @ref Advanced
2219 **/
2220 int CeedBasisGetGrad1D(CeedBasis basis, const CeedScalar **grad_1d) {
2221   bool is_tensor_basis;
2222 
2223   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2224   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2225   *grad_1d = basis->grad_1d;
2226   return CEED_ERROR_SUCCESS;
2227 }
2228 
2229 /**
2230   @brief Get divergence matrix of a `CeedBasis`
2231 
2232   @param[in]  basis `CeedBasis`
2233   @param[out] div   Variable to store divergence matrix
2234 
2235   @return An error code: 0 - success, otherwise - failure
2236 
2237   @ref Advanced
2238 **/
2239 int CeedBasisGetDiv(CeedBasis basis, const CeedScalar **div) {
2240   *div = basis->div;
2241   return CEED_ERROR_SUCCESS;
2242 }
2243 
2244 /**
2245   @brief Get curl matrix of a `CeedBasis`
2246 
2247   @param[in]  basis `CeedBasis`
2248   @param[out] curl  Variable to store curl matrix
2249 
2250   @return An error code: 0 - success, otherwise - failure
2251 
2252   @ref Advanced
2253 **/
2254 int CeedBasisGetCurl(CeedBasis basis, const CeedScalar **curl) {
2255   *curl = basis->curl;
2256   return CEED_ERROR_SUCCESS;
2257 }
2258 
2259 /**
2260   @brief Destroy a @ref  CeedBasis
2261 
2262   @param[in,out] basis `CeedBasis` to destroy
2263 
2264   @return An error code: 0 - success, otherwise - failure
2265 
2266   @ref User
2267 **/
2268 int CeedBasisDestroy(CeedBasis *basis) {
2269   if (!*basis || *basis == CEED_BASIS_NONE || --(*basis)->ref_count > 0) {
2270     *basis = NULL;
2271     return CEED_ERROR_SUCCESS;
2272   }
2273   if ((*basis)->Destroy) CeedCall((*basis)->Destroy(*basis));
2274   CeedCall(CeedTensorContractDestroy(&(*basis)->contract));
2275   CeedCall(CeedFree(&(*basis)->q_ref_1d));
2276   CeedCall(CeedFree(&(*basis)->q_weight_1d));
2277   CeedCall(CeedFree(&(*basis)->interp));
2278   CeedCall(CeedFree(&(*basis)->interp_1d));
2279   CeedCall(CeedFree(&(*basis)->grad));
2280   CeedCall(CeedFree(&(*basis)->grad_1d));
2281   CeedCall(CeedFree(&(*basis)->div));
2282   CeedCall(CeedFree(&(*basis)->curl));
2283   CeedCall(CeedVectorDestroy(&(*basis)->vec_chebyshev));
2284   CeedCall(CeedBasisDestroy(&(*basis)->basis_chebyshev));
2285   CeedCall(CeedDestroy(&(*basis)->ceed));
2286   CeedCall(CeedFree(basis));
2287   return CEED_ERROR_SUCCESS;
2288 }
2289 
2290 /**
2291   @brief Construct a Gauss-Legendre quadrature
2292 
2293   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-1` exactly)
2294   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2295   @param[out] q_weight_1d Array of length `Q` to hold the weights
2296 
2297   @return An error code: 0 - success, otherwise - failure
2298 
2299   @ref Utility
2300 **/
2301 int CeedGaussQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2302   CeedScalar P0, P1, P2, dP2, xi, wi, PI = 4.0 * atan(1.0);
2303 
2304   // Build q_ref_1d, q_weight_1d
2305   for (CeedInt i = 0; i <= Q / 2; i++) {
2306     // Guess
2307     xi = cos(PI * (CeedScalar)(2 * i + 1) / ((CeedScalar)(2 * Q)));
2308     // Pn(xi)
2309     P0 = 1.0;
2310     P1 = xi;
2311     P2 = 0.0;
2312     for (CeedInt j = 2; j <= Q; j++) {
2313       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2314       P0 = P1;
2315       P1 = P2;
2316     }
2317     // First Newton Step
2318     dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2319     xi  = xi - P2 / dP2;
2320     // Newton to convergence
2321     for (CeedInt k = 0; k < 100 && fabs(P2) > 10 * CEED_EPSILON; k++) {
2322       P0 = 1.0;
2323       P1 = xi;
2324       for (CeedInt j = 2; j <= Q; j++) {
2325         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2326         P0 = P1;
2327         P1 = P2;
2328       }
2329       dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2330       xi  = xi - P2 / dP2;
2331     }
2332     // Save xi, wi
2333     wi                     = 2.0 / ((1.0 - xi * xi) * dP2 * dP2);
2334     q_weight_1d[i]         = wi;
2335     q_weight_1d[Q - 1 - i] = wi;
2336     q_ref_1d[i]            = -xi;
2337     q_ref_1d[Q - 1 - i]    = xi;
2338   }
2339   return CEED_ERROR_SUCCESS;
2340 }
2341 
2342 /**
2343   @brief Construct a Gauss-Legendre-Lobatto quadrature
2344 
2345   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-3` exactly)
2346   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2347   @param[out] q_weight_1d Array of length `Q` to hold the weights
2348 
2349   @return An error code: 0 - success, otherwise - failure
2350 
2351   @ref Utility
2352 **/
2353 int CeedLobattoQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2354   CeedScalar P0, P1, P2, dP2, d2P2, xi, wi, PI = 4.0 * atan(1.0);
2355 
2356   // Build q_ref_1d, q_weight_1d
2357   // Set endpoints
2358   CeedCheck(Q > 1, NULL, CEED_ERROR_DIMENSION, "Cannot create Lobatto quadrature with Q=%" CeedInt_FMT " < 2 points", Q);
2359   wi = 2.0 / ((CeedScalar)(Q * (Q - 1)));
2360   if (q_weight_1d) {
2361     q_weight_1d[0]     = wi;
2362     q_weight_1d[Q - 1] = wi;
2363   }
2364   q_ref_1d[0]     = -1.0;
2365   q_ref_1d[Q - 1] = 1.0;
2366   // Interior
2367   for (CeedInt i = 1; i <= (Q - 1) / 2; i++) {
2368     // Guess
2369     xi = cos(PI * (CeedScalar)(i) / (CeedScalar)(Q - 1));
2370     // Pn(xi)
2371     P0 = 1.0;
2372     P1 = xi;
2373     P2 = 0.0;
2374     for (CeedInt j = 2; j < Q; j++) {
2375       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2376       P0 = P1;
2377       P1 = P2;
2378     }
2379     // First Newton step
2380     dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2381     d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2382     xi   = xi - dP2 / d2P2;
2383     // Newton to convergence
2384     for (CeedInt k = 0; k < 100 && fabs(dP2) > 10 * CEED_EPSILON; k++) {
2385       P0 = 1.0;
2386       P1 = xi;
2387       for (CeedInt j = 2; j < Q; j++) {
2388         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2389         P0 = P1;
2390         P1 = P2;
2391       }
2392       dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2393       d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2394       xi   = xi - dP2 / d2P2;
2395     }
2396     // Save xi, wi
2397     wi = 2.0 / (((CeedScalar)(Q * (Q - 1))) * P2 * P2);
2398     if (q_weight_1d) {
2399       q_weight_1d[i]         = wi;
2400       q_weight_1d[Q - 1 - i] = wi;
2401     }
2402     q_ref_1d[i]         = -xi;
2403     q_ref_1d[Q - 1 - i] = xi;
2404   }
2405   return CEED_ERROR_SUCCESS;
2406 }
2407 
2408 /// @}
2409