xref: /libCEED/interface/ceed-basis.c (revision 243afec996543dd9d0cad1d190b7ec15127a478e)
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 >= (CeedSize)total_num_points * (CeedSize)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, (CeedSize)total_num_points * (CeedSize)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 >= (CeedSize)total_num_points * (CeedSize)num_q_comp ||
350                                                      v_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)) ||
351                        (t_mode == CEED_NOTRANSPOSE && (v_length >= (CeedSize)total_num_points * (CeedSize)num_q_comp ||
352                                                        u_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)));
353       break;
354     case CEED_EVAL_GRAD:
355       has_good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= (CeedSize)total_num_points * (CeedSize)num_q_comp * (CeedSize)dim ||
356                                                      v_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)) ||
357                        (t_mode == CEED_NOTRANSPOSE && (v_length >= (CeedSize)total_num_points * (CeedSize)num_q_comp * (CeedSize)dim ||
358                                                        u_length >= (CeedSize)num_elem * (CeedSize)num_nodes * (CeedSize)num_comp)));
359       break;
360     case CEED_EVAL_WEIGHT:
361       has_good_dims = t_mode == CEED_NOTRANSPOSE && (v_length >= total_num_points);
362       break;
363       // LCOV_EXCL_START
364     case CEED_EVAL_NONE:
365     case CEED_EVAL_DIV:
366     case CEED_EVAL_CURL:
367       return CeedError(ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points not supported for %s", CeedEvalModes[eval_mode]);
368       // LCOV_EXCL_STOP
369   }
370   CeedCheck(has_good_dims, ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
371   return CEED_ERROR_SUCCESS;
372 }
373 
374 /**
375   @brief Default implimentation to apply basis evaluation from nodes to arbitrary points
376 
377   @param[in]  basis      `CeedBasis` to evaluate
378   @param[in]  apply_add  Sum result into target vector or overwrite
379   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
380                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
381   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
382   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
383                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
384   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
385                            @ref CEED_EVAL_GRAD to use gradients,
386                            @ref CEED_EVAL_WEIGHT to use quadrature weights
387   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
388   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
389   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
390 
391   @return An error code: 0 - success, otherwise - failure
392 
393   @ref Developer
394 **/
395 static int CeedBasisApplyAtPoints_Core(CeedBasis basis, bool apply_add, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode,
396                                        CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u, CeedVector v) {
397   CeedInt dim, num_comp, P_1d = 1, Q_1d = 1, total_num_points = num_points[0];
398   Ceed    ceed;
399 
400   CeedCall(CeedBasisGetCeed(basis, &ceed));
401   CeedCall(CeedBasisGetDimension(basis, &dim));
402   // Inserting check because clang-tidy doesn't understand this cannot occur
403   CeedCheck(dim > 0, ceed, CEED_ERROR_UNSUPPORTED, "Malformed CeedBasis, dim > 0 is required");
404   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
405   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
406   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
407 
408   // Default implementation
409   {
410     bool is_tensor_basis;
411 
412     CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
413     CeedCheck(is_tensor_basis, ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points only supported for tensor product bases");
414   }
415   CeedCheck(num_elem == 1, ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary  points only supported for a single element at a time");
416   if (eval_mode == CEED_EVAL_WEIGHT) {
417     CeedCall(CeedVectorSetValue(v, 1.0));
418     return CEED_ERROR_SUCCESS;
419   }
420   if (!basis->basis_chebyshev) {
421     // Build basis mapping from nodes to Chebyshev coefficients
422     CeedScalar       *chebyshev_interp_1d, *chebyshev_grad_1d, *chebyshev_q_weight_1d;
423     const CeedScalar *q_ref_1d;
424 
425     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_interp_1d));
426     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_grad_1d));
427     CeedCall(CeedCalloc(Q_1d, &chebyshev_q_weight_1d));
428     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
429     CeedCall(CeedBasisGetChebyshevInterp1D(basis, chebyshev_interp_1d));
430 
431     CeedCall(CeedVectorCreate(ceed, num_comp * CeedIntPow(Q_1d, dim), &basis->vec_chebyshev));
432     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d, Q_1d, chebyshev_interp_1d, chebyshev_grad_1d, q_ref_1d, chebyshev_q_weight_1d,
433                                      &basis->basis_chebyshev));
434 
435     // Cleanup
436     CeedCall(CeedFree(&chebyshev_interp_1d));
437     CeedCall(CeedFree(&chebyshev_grad_1d));
438     CeedCall(CeedFree(&chebyshev_q_weight_1d));
439   }
440 
441   // Create TensorContract object if needed, such as a basis from the GPU backends
442   if (!basis->contract) {
443     Ceed      ceed_ref;
444     CeedBasis basis_ref = NULL;
445 
446     CeedCall(CeedInit("/cpu/self", &ceed_ref));
447     // Only need matching tensor contraction dimensions, any type of basis will work
448     CeedCall(CeedBasisCreateTensorH1Lagrange(ceed_ref, dim, num_comp, P_1d, Q_1d, CEED_GAUSS, &basis_ref));
449     // Note - clang-tidy doesn't know basis_ref->contract must be valid here
450     CeedCheck(basis_ref && basis_ref->contract, ceed, CEED_ERROR_UNSUPPORTED, "Reference CPU ceed failed to create a tensor contraction object");
451     CeedCall(CeedTensorContractReferenceCopy(basis_ref->contract, &basis->contract));
452     CeedCall(CeedBasisDestroy(&basis_ref));
453     CeedCall(CeedDestroy(&ceed_ref));
454   }
455 
456   // Basis evaluation
457   switch (t_mode) {
458     case CEED_NOTRANSPOSE: {
459       // Nodes to arbitrary points
460       CeedScalar       *v_array;
461       const CeedScalar *chebyshev_coeffs, *x_array_read;
462 
463       // -- Interpolate to Chebyshev coefficients
464       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_NOTRANSPOSE, CEED_EVAL_INTERP, u, basis->vec_chebyshev));
465 
466       // -- Evaluate Chebyshev polynomials at arbitrary points
467       CeedCall(CeedVectorGetArrayRead(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
468       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
469       CeedCall(CeedVectorGetArrayWrite(v, CEED_MEM_HOST, &v_array));
470       switch (eval_mode) {
471         case CEED_EVAL_INTERP: {
472           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
473 
474           // ---- Values at point
475           for (CeedInt p = 0; p < total_num_points; p++) {
476             CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
477 
478             for (CeedInt d = 0; d < dim; d++) {
479               // ------ Tensor contract with current Chebyshev polynomial values
480               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
481               CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
482                                                d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
483               pre /= Q_1d;
484               post *= 1;
485             }
486             for (CeedInt c = 0; c < num_comp; c++) v_array[c * total_num_points + p] = tmp[dim % 2][c];
487           }
488           break;
489         }
490         case CEED_EVAL_GRAD: {
491           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
492 
493           // ---- Values at point
494           for (CeedInt p = 0; p < total_num_points; p++) {
495             // Dim**2 contractions, apply grad when pass == dim
496             for (CeedInt pass = 0; pass < dim; pass++) {
497               CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
498 
499               for (CeedInt d = 0; d < dim; d++) {
500                 // ------ Tensor contract with current Chebyshev polynomial values
501                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
502                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
503                 CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
504                                                  d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
505                 pre /= Q_1d;
506                 post *= 1;
507               }
508               for (CeedInt c = 0; c < num_comp; c++) v_array[(pass * num_comp + c) * total_num_points + p] = tmp[dim % 2][c];
509             }
510           }
511           break;
512         }
513         default:
514           // Nothing to do, excluded above
515           break;
516       }
517       CeedCall(CeedVectorRestoreArrayRead(basis->vec_chebyshev, &chebyshev_coeffs));
518       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
519       CeedCall(CeedVectorRestoreArray(v, &v_array));
520       break;
521     }
522     case CEED_TRANSPOSE: {
523       // Note: No switch on e_mode here because only CEED_EVAL_INTERP is supported at this time
524       // Arbitrary points to nodes
525       CeedScalar       *chebyshev_coeffs;
526       const CeedScalar *u_array, *x_array_read;
527 
528       // -- Transpose of evaluation of Chebyshev polynomials at arbitrary points
529       CeedCall(CeedVectorGetArrayWrite(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
530       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
531       CeedCall(CeedVectorGetArrayRead(u, CEED_MEM_HOST, &u_array));
532 
533       switch (eval_mode) {
534         case CEED_EVAL_INTERP: {
535           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
536 
537           // ---- Values at point
538           for (CeedInt p = 0; p < total_num_points; p++) {
539             CeedInt pre = num_comp * 1, post = 1;
540 
541             for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[c * total_num_points + p];
542             for (CeedInt d = 0; d < dim; d++) {
543               // ------ Tensor contract with current Chebyshev polynomial values
544               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
545               CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode, p > 0 && d == (dim - 1), tmp[d % 2],
546                                                d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
547               pre /= 1;
548               post *= Q_1d;
549             }
550           }
551           break;
552         }
553         case CEED_EVAL_GRAD: {
554           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
555 
556           // ---- Values at point
557           for (CeedInt p = 0; p < total_num_points; p++) {
558             // Dim**2 contractions, apply grad when pass == dim
559             for (CeedInt pass = 0; pass < dim; pass++) {
560               CeedInt pre = num_comp * 1, post = 1;
561 
562               for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[(pass * num_comp + c) * total_num_points + p];
563               for (CeedInt d = 0; d < dim; d++) {
564                 // ------ Tensor contract with current Chebyshev polynomial values
565                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
566                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * total_num_points + p], Q_1d, chebyshev_x));
567                 CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode,
568                                                  (p > 0 || (p == 0 && pass > 0)) && d == (dim - 1), tmp[d % 2],
569                                                  d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
570                 pre /= 1;
571                 post *= Q_1d;
572               }
573             }
574           }
575           break;
576         }
577         default:
578           // Nothing to do, excluded above
579           break;
580       }
581       CeedCall(CeedVectorRestoreArray(basis->vec_chebyshev, &chebyshev_coeffs));
582       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
583       CeedCall(CeedVectorRestoreArrayRead(u, &u_array));
584 
585       // -- Interpolate transpose from Chebyshev coefficients
586       if (apply_add) CeedCall(CeedBasisApplyAdd(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
587       else CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
588       break;
589     }
590   }
591   return CEED_ERROR_SUCCESS;
592 }
593 
594 /// @}
595 
596 /// ----------------------------------------------------------------------------
597 /// Ceed Backend API
598 /// ----------------------------------------------------------------------------
599 /// @addtogroup CeedBasisBackend
600 /// @{
601 
602 /**
603   @brief Return collocated gradient matrix
604 
605   @param[in]  basis         `CeedBasis`
606   @param[out] collo_grad_1d Row-major (`Q_1d * Q_1d`) matrix expressing derivatives of basis functions at quadrature points
607 
608   @return An error code: 0 - success, otherwise - failure
609 
610   @ref Backend
611 **/
612 int CeedBasisGetCollocatedGrad(CeedBasis basis, CeedScalar *collo_grad_1d) {
613   Ceed              ceed;
614   CeedInt           P_1d, Q_1d;
615   CeedScalar       *interp_1d_pinv;
616   const CeedScalar *grad_1d, *interp_1d;
617 
618   // Note: This function is for backend use, so all errors are terminal and we do not need to clean up memory on failure.
619   CeedCall(CeedBasisGetCeed(basis, &ceed));
620   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
621   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
622 
623   // Compute interp_1d^+, pseudoinverse of interp_1d
624   CeedCall(CeedCalloc(P_1d * Q_1d, &interp_1d_pinv));
625   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
626   CeedCall(CeedMatrixPseudoinverse(ceed, interp_1d, Q_1d, P_1d, interp_1d_pinv));
627   CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
628   CeedCall(CeedMatrixMatrixMultiply(ceed, grad_1d, (const CeedScalar *)interp_1d_pinv, collo_grad_1d, Q_1d, Q_1d, P_1d));
629 
630   CeedCall(CeedFree(&interp_1d_pinv));
631   return CEED_ERROR_SUCCESS;
632 }
633 
634 /**
635   @brief Return 1D interpolation matrix to Chebyshev polynomial coefficients on quadrature space
636 
637   @param[in]  basis               `CeedBasis`
638   @param[out] chebyshev_interp_1d Row-major (`P_1d * Q_1d`) matrix interpolating from basis nodes to Chebyshev polynomial coefficients
639 
640   @return An error code: 0 - success, otherwise - failure
641 
642   @ref Backend
643 **/
644 int CeedBasisGetChebyshevInterp1D(CeedBasis basis, CeedScalar *chebyshev_interp_1d) {
645   CeedInt           P_1d, Q_1d;
646   CeedScalar       *C, *chebyshev_coeffs_1d_inv;
647   const CeedScalar *interp_1d, *q_ref_1d;
648   Ceed              ceed;
649 
650   CeedCall(CeedBasisGetCeed(basis, &ceed));
651   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
652   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
653 
654   // Build coefficient matrix
655   // -- Note: Clang-tidy needs this check
656   CeedCheck((P_1d > 0) && (Q_1d > 0), ceed, CEED_ERROR_INCOMPATIBLE, "CeedBasis dimensions are malformed");
657   CeedCall(CeedCalloc(Q_1d * Q_1d, &C));
658   CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
659   for (CeedInt i = 0; i < Q_1d; i++) CeedCall(CeedChebyshevPolynomialsAtPoint(q_ref_1d[i], Q_1d, &C[i * Q_1d]));
660 
661   // Compute C^+, pseudoinverse of coefficient matrix
662   CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_coeffs_1d_inv));
663   CeedCall(CeedMatrixPseudoinverse(ceed, C, Q_1d, Q_1d, chebyshev_coeffs_1d_inv));
664 
665   // Build mapping from nodes to Chebyshev coefficients
666   CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
667   CeedCall(CeedMatrixMatrixMultiply(ceed, chebyshev_coeffs_1d_inv, interp_1d, chebyshev_interp_1d, Q_1d, P_1d, Q_1d));
668 
669   // Cleanup
670   CeedCall(CeedFree(&C));
671   CeedCall(CeedFree(&chebyshev_coeffs_1d_inv));
672   return CEED_ERROR_SUCCESS;
673 }
674 
675 /**
676   @brief Get tensor status for given `CeedBasis`
677 
678   @param[in]  basis     `CeedBasis`
679   @param[out] is_tensor Variable to store tensor status
680 
681   @return An error code: 0 - success, otherwise - failure
682 
683   @ref Backend
684 **/
685 int CeedBasisIsTensor(CeedBasis basis, bool *is_tensor) {
686   *is_tensor = basis->is_tensor_basis;
687   return CEED_ERROR_SUCCESS;
688 }
689 
690 /**
691   @brief Get backend data of a `CeedBasis`
692 
693   @param[in]  basis `CeedBasis`
694   @param[out] data  Variable to store data
695 
696   @return An error code: 0 - success, otherwise - failure
697 
698   @ref Backend
699 **/
700 int CeedBasisGetData(CeedBasis basis, void *data) {
701   *(void **)data = basis->data;
702   return CEED_ERROR_SUCCESS;
703 }
704 
705 /**
706   @brief Set backend data of a `CeedBasis`
707 
708   @param[in,out] basis  `CeedBasis`
709   @param[in]     data   Data to set
710 
711   @return An error code: 0 - success, otherwise - failure
712 
713   @ref Backend
714 **/
715 int CeedBasisSetData(CeedBasis basis, void *data) {
716   basis->data = data;
717   return CEED_ERROR_SUCCESS;
718 }
719 
720 /**
721   @brief Increment the reference counter for a `CeedBasis`
722 
723   @param[in,out] basis `CeedBasis` to increment the reference counter
724 
725   @return An error code: 0 - success, otherwise - failure
726 
727   @ref Backend
728 **/
729 int CeedBasisReference(CeedBasis basis) {
730   basis->ref_count++;
731   return CEED_ERROR_SUCCESS;
732 }
733 
734 /**
735   @brief Get number of Q-vector components for given `CeedBasis`
736 
737   @param[in]  basis     `CeedBasis`
738   @param[in]  eval_mode @ref CEED_EVAL_INTERP to use interpolated values,
739                           @ref CEED_EVAL_GRAD to use gradients,
740                           @ref CEED_EVAL_DIV to use divergence,
741                           @ref CEED_EVAL_CURL to use curl
742   @param[out] q_comp    Variable to store number of Q-vector components of basis
743 
744   @return An error code: 0 - success, otherwise - failure
745 
746   @ref Backend
747 **/
748 int CeedBasisGetNumQuadratureComponents(CeedBasis basis, CeedEvalMode eval_mode, CeedInt *q_comp) {
749   CeedInt dim;
750 
751   CeedCall(CeedBasisGetDimension(basis, &dim));
752   switch (eval_mode) {
753     case CEED_EVAL_INTERP: {
754       CeedFESpace fe_space;
755 
756       CeedCall(CeedBasisGetFESpace(basis, &fe_space));
757       *q_comp = (fe_space == CEED_FE_SPACE_H1) ? 1 : dim;
758     } break;
759     case CEED_EVAL_GRAD:
760       *q_comp = dim;
761       break;
762     case CEED_EVAL_DIV:
763       *q_comp = 1;
764       break;
765     case CEED_EVAL_CURL:
766       *q_comp = (dim < 3) ? 1 : dim;
767       break;
768     case CEED_EVAL_NONE:
769     case CEED_EVAL_WEIGHT:
770       *q_comp = 1;
771       break;
772   }
773   return CEED_ERROR_SUCCESS;
774 }
775 
776 /**
777   @brief Estimate number of FLOPs required to apply `CeedBasis` in `t_mode` and `eval_mode`
778 
779   @param[in]  basis     `CeedBasis` to estimate FLOPs for
780   @param[in]  t_mode    Apply basis or transpose
781   @param[in]  eval_mode @ref CeedEvalMode
782   @param[out] flops     Address of variable to hold FLOPs estimate
783 
784   @ref Backend
785 **/
786 int CeedBasisGetFlopsEstimate(CeedBasis basis, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedSize *flops) {
787   bool is_tensor;
788 
789   CeedCall(CeedBasisIsTensor(basis, &is_tensor));
790   if (is_tensor) {
791     CeedInt dim, num_comp, P_1d, Q_1d;
792 
793     CeedCall(CeedBasisGetDimension(basis, &dim));
794     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
795     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
796     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
797     if (t_mode == CEED_TRANSPOSE) {
798       P_1d = Q_1d;
799       Q_1d = P_1d;
800     }
801     CeedInt tensor_flops = 0, pre = num_comp * CeedIntPow(P_1d, dim - 1), post = 1;
802     for (CeedInt d = 0; d < dim; d++) {
803       tensor_flops += 2 * pre * P_1d * post * Q_1d;
804       pre /= P_1d;
805       post *= Q_1d;
806     }
807     switch (eval_mode) {
808       case CEED_EVAL_NONE:
809         *flops = 0;
810         break;
811       case CEED_EVAL_INTERP:
812         *flops = tensor_flops;
813         break;
814       case CEED_EVAL_GRAD:
815         *flops = tensor_flops * 2;
816         break;
817       case CEED_EVAL_DIV:
818       case CEED_EVAL_CURL: {
819         // LCOV_EXCL_START
820         return CeedError(CeedBasisReturnCeed(basis), CEED_ERROR_INCOMPATIBLE, "Tensor basis evaluation for %s not supported",
821                          CeedEvalModes[eval_mode]);
822         break;
823         // LCOV_EXCL_STOP
824       }
825       case CEED_EVAL_WEIGHT:
826         *flops = dim * CeedIntPow(Q_1d, dim);
827         break;
828     }
829   } else {
830     CeedInt dim, num_comp, q_comp, num_nodes, num_qpts;
831 
832     CeedCall(CeedBasisGetDimension(basis, &dim));
833     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
834     CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
835     CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
836     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
837     switch (eval_mode) {
838       case CEED_EVAL_NONE:
839         *flops = 0;
840         break;
841       case CEED_EVAL_INTERP:
842       case CEED_EVAL_GRAD:
843       case CEED_EVAL_DIV:
844       case CEED_EVAL_CURL:
845         *flops = num_nodes * num_qpts * num_comp * q_comp;
846         break;
847       case CEED_EVAL_WEIGHT:
848         *flops = 0;
849         break;
850     }
851   }
852   return CEED_ERROR_SUCCESS;
853 }
854 
855 /**
856   @brief Get `CeedFESpace` for a `CeedBasis`
857 
858   @param[in]  basis    `CeedBasis`
859   @param[out] fe_space Variable to store `CeedFESpace`
860 
861   @return An error code: 0 - success, otherwise - failure
862 
863   @ref Backend
864 **/
865 int CeedBasisGetFESpace(CeedBasis basis, CeedFESpace *fe_space) {
866   *fe_space = basis->fe_space;
867   return CEED_ERROR_SUCCESS;
868 }
869 
870 /**
871   @brief Get dimension for given `CeedElemTopology`
872 
873   @param[in]  topo `CeedElemTopology`
874   @param[out] dim  Variable to store dimension of topology
875 
876   @return An error code: 0 - success, otherwise - failure
877 
878   @ref Backend
879 **/
880 int CeedBasisGetTopologyDimension(CeedElemTopology topo, CeedInt *dim) {
881   *dim = (CeedInt)topo >> 16;
882   return CEED_ERROR_SUCCESS;
883 }
884 
885 /**
886   @brief Get `CeedTensorContract` of a `CeedBasis`
887 
888   @param[in]  basis     `CeedBasis`
889   @param[out] contract  Variable to store `CeedTensorContract`
890 
891   @return An error code: 0 - success, otherwise - failure
892 
893   @ref Backend
894 **/
895 int CeedBasisGetTensorContract(CeedBasis basis, CeedTensorContract *contract) {
896   *contract = basis->contract;
897   return CEED_ERROR_SUCCESS;
898 }
899 
900 /**
901   @brief Set `CeedTensorContract` of a `CeedBasis`
902 
903   @param[in,out] basis    `CeedBasis`
904   @param[in]     contract `CeedTensorContract` to set
905 
906   @return An error code: 0 - success, otherwise - failure
907 
908   @ref Backend
909 **/
910 int CeedBasisSetTensorContract(CeedBasis basis, CeedTensorContract contract) {
911   basis->contract = contract;
912   CeedCall(CeedTensorContractReference(contract));
913   return CEED_ERROR_SUCCESS;
914 }
915 
916 /**
917   @brief Return a reference implementation of matrix multiplication \f$C = A B\f$.
918 
919   Note: This is a reference implementation for CPU `CeedScalar` pointers that is not intended for high performance.
920 
921   @param[in]  ceed  `Ceed` context for error handling
922   @param[in]  mat_A Row-major matrix `A`
923   @param[in]  mat_B Row-major matrix `B`
924   @param[out] mat_C Row-major output matrix `C`
925   @param[in]  m     Number of rows of `C`
926   @param[in]  n     Number of columns of `C`
927   @param[in]  kk    Number of columns of `A`/rows of `B`
928 
929   @return An error code: 0 - success, otherwise - failure
930 
931   @ref Utility
932 **/
933 int CeedMatrixMatrixMultiply(Ceed ceed, const CeedScalar *mat_A, const CeedScalar *mat_B, CeedScalar *mat_C, CeedInt m, CeedInt n, CeedInt kk) {
934   for (CeedInt i = 0; i < m; i++) {
935     for (CeedInt j = 0; j < n; j++) {
936       CeedScalar sum = 0;
937 
938       for (CeedInt k = 0; k < kk; k++) sum += mat_A[k + i * kk] * mat_B[j + k * n];
939       mat_C[j + i * n] = sum;
940     }
941   }
942   return CEED_ERROR_SUCCESS;
943 }
944 
945 /**
946   @brief Return QR Factorization of a matrix
947 
948   @param[in]     ceed `Ceed` context for error handling
949   @param[in,out] mat  Row-major matrix to be factorized in place
950   @param[in,out] tau  Vector of length `m` of scaling factors
951   @param[in]     m    Number of rows
952   @param[in]     n    Number of columns
953 
954   @return An error code: 0 - success, otherwise - failure
955 
956   @ref Utility
957 **/
958 int CeedQRFactorization(Ceed ceed, CeedScalar *mat, CeedScalar *tau, CeedInt m, CeedInt n) {
959   CeedScalar v[m];
960 
961   // Check matrix shape
962   CeedCheck(n <= m, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute QR factorization with n > m");
963 
964   for (CeedInt i = 0; i < n; i++) {
965     CeedScalar sigma = 0.0;
966 
967     if (i >= m - 1) {  // last row of matrix, no reflection needed
968       tau[i] = 0.;
969       break;
970     }
971     // Calculate Householder vector, magnitude
972     v[i] = mat[i + n * i];
973     for (CeedInt j = i + 1; j < m; j++) {
974       v[j] = mat[i + n * j];
975       sigma += v[j] * v[j];
976     }
977     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:m]
978     const CeedScalar R_ii = -copysign(norm, v[i]);
979 
980     v[i] -= R_ii;
981     // norm of v[i:m] after modification above and scaling below
982     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
983     //   tau = 2 / (norm*norm)
984     tau[i] = 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
985     for (CeedInt j = i + 1; j < m; j++) v[j] /= v[i];
986 
987     // Apply Householder reflector to lower right panel
988     CeedHouseholderReflect(&mat[i * n + i + 1], &v[i], tau[i], m - i, n - i - 1, n, 1);
989     // Save v
990     mat[i + n * i] = R_ii;
991     for (CeedInt j = i + 1; j < m; j++) mat[i + n * j] = v[j];
992   }
993   return CEED_ERROR_SUCCESS;
994 }
995 
996 /**
997   @brief Apply Householder Q matrix
998 
999   Compute `mat_A = mat_Q mat_A`, where `mat_Q` is \f$m \times m\f$ and `mat_A` is \f$m \times n\f$.
1000 
1001   @param[in,out] mat_A  Matrix to apply Householder Q to, in place
1002   @param[in]     mat_Q  Householder Q matrix
1003   @param[in]     tau    Householder scaling factors
1004   @param[in]     t_mode Transpose mode for application
1005   @param[in]     m      Number of rows in `A`
1006   @param[in]     n      Number of columns in `A`
1007   @param[in]     k      Number of elementary reflectors in Q, `k < m`
1008   @param[in]     row    Row stride in `A`
1009   @param[in]     col    Col stride in `A`
1010 
1011   @return An error code: 0 - success, otherwise - failure
1012 
1013   @ref Utility
1014 **/
1015 int CeedHouseholderApplyQ(CeedScalar *mat_A, const CeedScalar *mat_Q, const CeedScalar *tau, CeedTransposeMode t_mode, CeedInt m, CeedInt n,
1016                           CeedInt k, CeedInt row, CeedInt col) {
1017   CeedScalar *v;
1018 
1019   CeedCall(CeedMalloc(m, &v));
1020   for (CeedInt ii = 0; ii < k; ii++) {
1021     CeedInt i = t_mode == CEED_TRANSPOSE ? ii : k - 1 - ii;
1022     for (CeedInt j = i + 1; j < m; j++) v[j] = mat_Q[j * k + i];
1023     // Apply Householder reflector (I - tau v v^T) collo_grad_1d^T
1024     CeedCall(CeedHouseholderReflect(&mat_A[i * row], &v[i], tau[i], m - i, n, row, col));
1025   }
1026   CeedCall(CeedFree(&v));
1027   return CEED_ERROR_SUCCESS;
1028 }
1029 
1030 /**
1031   @brief Return pseudoinverse of a matrix
1032 
1033   @param[in]     ceed      Ceed context for error handling
1034   @param[in]     mat       Row-major matrix to compute pseudoinverse of
1035   @param[in]     m         Number of rows
1036   @param[in]     n         Number of columns
1037   @param[out]    mat_pinv  Row-major pseudoinverse matrix
1038 
1039   @return An error code: 0 - success, otherwise - failure
1040 
1041   @ref Utility
1042 **/
1043 int CeedMatrixPseudoinverse(Ceed ceed, const CeedScalar *mat, CeedInt m, CeedInt n, CeedScalar *mat_pinv) {
1044   CeedScalar *tau, *I, *mat_copy;
1045 
1046   CeedCall(CeedCalloc(m, &tau));
1047   CeedCall(CeedCalloc(m * m, &I));
1048   CeedCall(CeedCalloc(m * n, &mat_copy));
1049   memcpy(mat_copy, mat, m * n * sizeof mat[0]);
1050 
1051   // QR Factorization, mat = Q R
1052   CeedCall(CeedQRFactorization(ceed, mat_copy, tau, m, n));
1053 
1054   // -- Apply Q^T, I = Q^T * I
1055   for (CeedInt i = 0; i < m; i++) I[i * m + i] = 1.0;
1056   CeedCall(CeedHouseholderApplyQ(I, mat_copy, tau, CEED_TRANSPOSE, m, m, n, m, 1));
1057   // -- Apply R_inv, mat_pinv = R_inv * Q^T
1058   for (CeedInt j = 0; j < m; j++) {  // Column j
1059     mat_pinv[j + m * (n - 1)] = I[j + m * (n - 1)] / mat_copy[n * n - 1];
1060     for (CeedInt i = n - 2; i >= 0; i--) {  // Row i
1061       mat_pinv[j + m * i] = I[j + m * i];
1062       for (CeedInt k = i + 1; k < n; k++) mat_pinv[j + m * i] -= mat_copy[k + n * i] * mat_pinv[j + m * k];
1063       mat_pinv[j + m * i] /= mat_copy[i + n * i];
1064     }
1065   }
1066 
1067   // Cleanup
1068   CeedCall(CeedFree(&I));
1069   CeedCall(CeedFree(&tau));
1070   CeedCall(CeedFree(&mat_copy));
1071   return CEED_ERROR_SUCCESS;
1072 }
1073 
1074 /**
1075   @brief Return symmetric Schur decomposition of the symmetric matrix mat via symmetric QR factorization
1076 
1077   @param[in]     ceed   `Ceed` context for error handling
1078   @param[in,out] mat    Row-major matrix to be factorized in place
1079   @param[out]    lambda Vector of length n of eigenvalues
1080   @param[in]     n      Number of rows/columns
1081 
1082   @return An error code: 0 - success, otherwise - failure
1083 
1084   @ref Utility
1085 **/
1086 CeedPragmaOptimizeOff
1087 int CeedSymmetricSchurDecomposition(Ceed ceed, CeedScalar *mat, CeedScalar *lambda, CeedInt n) {
1088   // Check bounds for clang-tidy
1089   CeedCheck(n > 1, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute symmetric Schur decomposition of scalars");
1090 
1091   CeedScalar v[n - 1], tau[n - 1], mat_T[n * n];
1092 
1093   // Copy mat to mat_T and set mat to I
1094   memcpy(mat_T, mat, n * n * sizeof(mat[0]));
1095   for (CeedInt i = 0; i < n; i++) {
1096     for (CeedInt j = 0; j < n; j++) mat[j + n * i] = (i == j) ? 1 : 0;
1097   }
1098 
1099   // Reduce to tridiagonal
1100   for (CeedInt i = 0; i < n - 1; i++) {
1101     // Calculate Householder vector, magnitude
1102     CeedScalar sigma = 0.0;
1103 
1104     v[i] = mat_T[i + n * (i + 1)];
1105     for (CeedInt j = i + 1; j < n - 1; j++) {
1106       v[j] = mat_T[i + n * (j + 1)];
1107       sigma += v[j] * v[j];
1108     }
1109     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:n-1]
1110     const CeedScalar R_ii = -copysign(norm, v[i]);
1111 
1112     v[i] -= R_ii;
1113     // norm of v[i:m] after modification above and scaling below
1114     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
1115     //   tau = 2 / (norm*norm)
1116     tau[i] = i == n - 2 ? 2 : 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
1117     for (CeedInt j = i + 1; j < n - 1; j++) v[j] /= v[i];
1118 
1119     // Update sub and super diagonal
1120     for (CeedInt j = i + 2; j < n; j++) {
1121       mat_T[i + n * j] = 0;
1122       mat_T[j + n * i] = 0;
1123     }
1124     // Apply symmetric Householder reflector to lower right panel
1125     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1126     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), 1, n);
1127 
1128     // Save v
1129     mat_T[i + n * (i + 1)] = R_ii;
1130     mat_T[(i + 1) + n * i] = R_ii;
1131     for (CeedInt j = i + 1; j < n - 1; j++) {
1132       mat_T[i + n * (j + 1)] = v[j];
1133     }
1134   }
1135   // Backwards accumulation of Q
1136   for (CeedInt i = n - 2; i >= 0; i--) {
1137     if (tau[i] > 0.0) {
1138       v[i] = 1;
1139       for (CeedInt j = i + 1; j < n - 1; j++) {
1140         v[j]                   = mat_T[i + n * (j + 1)];
1141         mat_T[i + n * (j + 1)] = 0;
1142       }
1143       CeedHouseholderReflect(&mat[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
1144     }
1145   }
1146 
1147   // Reduce sub and super diagonal
1148   CeedInt    p = 0, q = 0, itr = 0, max_itr = n * n * n * n;
1149   CeedScalar tol = CEED_EPSILON;
1150 
1151   while (itr < max_itr) {
1152     // Update p, q, size of reduced portions of diagonal
1153     p = 0;
1154     q = 0;
1155     for (CeedInt i = n - 2; i >= 0; i--) {
1156       if (fabs(mat_T[i + n * (i + 1)]) < tol) q += 1;
1157       else break;
1158     }
1159     for (CeedInt i = 0; i < n - q - 1; i++) {
1160       if (fabs(mat_T[i + n * (i + 1)]) < tol) p += 1;
1161       else break;
1162     }
1163     if (q == n - 1) break;  // Finished reducing
1164 
1165     // Reduce tridiagonal portion
1166     CeedScalar t_nn = mat_T[(n - 1 - q) + n * (n - 1 - q)], t_nnm1 = mat_T[(n - 2 - q) + n * (n - 1 - q)];
1167     CeedScalar d  = (mat_T[(n - 2 - q) + n * (n - 2 - q)] - t_nn) / 2;
1168     CeedScalar mu = t_nn - t_nnm1 * t_nnm1 / (d + copysign(sqrt(d * d + t_nnm1 * t_nnm1), d));
1169     CeedScalar x  = mat_T[p + n * p] - mu;
1170     CeedScalar z  = mat_T[p + n * (p + 1)];
1171 
1172     for (CeedInt k = p; k < n - q - 1; k++) {
1173       // Compute Givens rotation
1174       CeedScalar c = 1, s = 0;
1175 
1176       if (fabs(z) > tol) {
1177         if (fabs(z) > fabs(x)) {
1178           const CeedScalar tau = -x / z;
1179 
1180           s = 1 / sqrt(1 + tau * tau);
1181           c = s * tau;
1182         } else {
1183           const CeedScalar tau = -z / x;
1184 
1185           c = 1 / sqrt(1 + tau * tau);
1186           s = c * tau;
1187         }
1188       }
1189 
1190       // Apply Givens rotation to T
1191       CeedGivensRotation(mat_T, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1192       CeedGivensRotation(mat_T, c, s, CEED_TRANSPOSE, k, k + 1, n, n);
1193 
1194       // Apply Givens rotation to Q
1195       CeedGivensRotation(mat, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
1196 
1197       // Update x, z
1198       if (k < n - q - 2) {
1199         x = mat_T[k + n * (k + 1)];
1200         z = mat_T[k + n * (k + 2)];
1201       }
1202     }
1203     itr++;
1204   }
1205 
1206   // Save eigenvalues
1207   for (CeedInt i = 0; i < n; i++) lambda[i] = mat_T[i + n * i];
1208 
1209   // Check convergence
1210   CeedCheck(itr < max_itr || q > n, ceed, CEED_ERROR_MINOR, "Symmetric QR failed to converge");
1211   return CEED_ERROR_SUCCESS;
1212 }
1213 CeedPragmaOptimizeOn
1214 
1215 /**
1216   @brief Return Simultaneous Diagonalization of two matrices.
1217 
1218   This solves the generalized eigenvalue problem `A x = lambda B x`, where `A` and `B` are symmetric and `B` is positive definite.
1219   We generate the matrix `X` and vector `Lambda` such that `X^T A X = Lambda` and `X^T B X = I`.
1220   This is equivalent to the LAPACK routine 'sygv' with `TYPE = 1`.
1221 
1222   @param[in]  ceed   `Ceed` context for error handling
1223   @param[in]  mat_A  Row-major matrix to be factorized with eigenvalues
1224   @param[in]  mat_B  Row-major matrix to be factorized to identity
1225   @param[out] mat_X  Row-major orthogonal matrix
1226   @param[out] lambda Vector of length `n` of generalized eigenvalues
1227   @param[in]  n      Number of rows/columns
1228 
1229   @return An error code: 0 - success, otherwise - failure
1230 
1231   @ref Utility
1232 **/
1233 CeedPragmaOptimizeOff
1234 int CeedSimultaneousDiagonalization(Ceed ceed, CeedScalar *mat_A, CeedScalar *mat_B, CeedScalar *mat_X, CeedScalar *lambda, CeedInt n) {
1235   CeedScalar *mat_C, *mat_G, *vec_D;
1236 
1237   CeedCall(CeedCalloc(n * n, &mat_C));
1238   CeedCall(CeedCalloc(n * n, &mat_G));
1239   CeedCall(CeedCalloc(n, &vec_D));
1240 
1241   // Compute B = G D G^T
1242   memcpy(mat_G, mat_B, n * n * sizeof(mat_B[0]));
1243   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_G, vec_D, n));
1244 
1245   // Sort eigenvalues
1246   for (CeedInt i = n - 1; i >= 0; i--) {
1247     for (CeedInt j = 0; j < i; j++) {
1248       if (fabs(vec_D[j]) > fabs(vec_D[j + 1])) {
1249         CeedScalarSwap(vec_D[j], vec_D[j + 1]);
1250         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_G[k * n + j], mat_G[k * n + j + 1]);
1251       }
1252     }
1253   }
1254 
1255   // Compute C = (G D^1/2)^-1 A (G D^1/2)^-T
1256   //           = D^-1/2 G^T A G D^-1/2
1257   // -- D = D^-1/2
1258   for (CeedInt i = 0; i < n; i++) vec_D[i] = 1. / sqrt(vec_D[i]);
1259   // -- G = G D^-1/2
1260   // -- C = D^-1/2 G^T
1261   for (CeedInt i = 0; i < n; i++) {
1262     for (CeedInt j = 0; j < n; j++) {
1263       mat_G[i * n + j] *= vec_D[j];
1264       mat_C[j * n + i] = mat_G[i * n + j];
1265     }
1266   }
1267   // -- X = (D^-1/2 G^T) A
1268   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_C, (const CeedScalar *)mat_A, mat_X, n, n, n));
1269   // -- C = (D^-1/2 G^T A) (G D^-1/2)
1270   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_X, (const CeedScalar *)mat_G, mat_C, n, n, n));
1271 
1272   // Compute Q^T C Q = lambda
1273   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_C, lambda, n));
1274 
1275   // Sort eigenvalues
1276   for (CeedInt i = n - 1; i >= 0; i--) {
1277     for (CeedInt j = 0; j < i; j++) {
1278       if (fabs(lambda[j]) > fabs(lambda[j + 1])) {
1279         CeedScalarSwap(lambda[j], lambda[j + 1]);
1280         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_C[k * n + j], mat_C[k * n + j + 1]);
1281       }
1282     }
1283   }
1284 
1285   // Set X = (G D^1/2)^-T Q
1286   //       = G D^-1/2 Q
1287   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_G, (const CeedScalar *)mat_C, mat_X, n, n, n));
1288 
1289   // Cleanup
1290   CeedCall(CeedFree(&mat_C));
1291   CeedCall(CeedFree(&mat_G));
1292   CeedCall(CeedFree(&vec_D));
1293   return CEED_ERROR_SUCCESS;
1294 }
1295 CeedPragmaOptimizeOn
1296 
1297 /// @}
1298 
1299 /// ----------------------------------------------------------------------------
1300 /// CeedBasis Public API
1301 /// ----------------------------------------------------------------------------
1302 /// @addtogroup CeedBasisUser
1303 /// @{
1304 
1305 /**
1306   @brief Create a tensor-product basis for \f$H^1\f$ discretizations
1307 
1308   @param[in]  ceed        `Ceed` object used to create the `CeedBasis`
1309   @param[in]  dim         Topological dimension
1310   @param[in]  num_comp    Number of field components (1 for scalar fields)
1311   @param[in]  P_1d        Number of nodes in one dimension
1312   @param[in]  Q_1d        Number of quadrature points in one dimension
1313   @param[in]  interp_1d   Row-major (`Q_1d * P_1d`) matrix expressing the values of nodal basis functions at quadrature points
1314   @param[in]  grad_1d     Row-major (`Q_1d * P_1d`) matrix expressing derivatives of nodal basis functions at quadrature points
1315   @param[in]  q_ref_1d    Array of length `Q_1d` holding the locations of quadrature points on the 1D reference element `[-1, 1]`
1316   @param[in]  q_weight_1d Array of length `Q_1d` holding the quadrature weights on the reference element
1317   @param[out] basis       Address of the variable where the newly created `CeedBasis` will be stored
1318 
1319   @return An error code: 0 - success, otherwise - failure
1320 
1321   @ref User
1322 **/
1323 int CeedBasisCreateTensorH1(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P_1d, CeedInt Q_1d, const CeedScalar *interp_1d,
1324                             const CeedScalar *grad_1d, const CeedScalar *q_ref_1d, const CeedScalar *q_weight_1d, CeedBasis *basis) {
1325   if (!ceed->BasisCreateTensorH1) {
1326     Ceed delegate;
1327 
1328     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1329     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateTensorH1");
1330     CeedCall(CeedBasisCreateTensorH1(delegate, dim, num_comp, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1331     return CEED_ERROR_SUCCESS;
1332   }
1333 
1334   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1335   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1336   CeedCheck(P_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1337   CeedCheck(Q_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1338 
1339   CeedElemTopology topo = dim == 1 ? CEED_TOPOLOGY_LINE : dim == 2 ? CEED_TOPOLOGY_QUAD : CEED_TOPOLOGY_HEX;
1340 
1341   CeedCall(CeedCalloc(1, basis));
1342   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1343   (*basis)->ref_count       = 1;
1344   (*basis)->is_tensor_basis = true;
1345   (*basis)->dim             = dim;
1346   (*basis)->topo            = topo;
1347   (*basis)->num_comp        = num_comp;
1348   (*basis)->P_1d            = P_1d;
1349   (*basis)->Q_1d            = Q_1d;
1350   (*basis)->P               = CeedIntPow(P_1d, dim);
1351   (*basis)->Q               = CeedIntPow(Q_1d, dim);
1352   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1353   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_ref_1d));
1354   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_weight_1d));
1355   if (q_ref_1d) memcpy((*basis)->q_ref_1d, q_ref_1d, Q_1d * sizeof(q_ref_1d[0]));
1356   if (q_weight_1d) memcpy((*basis)->q_weight_1d, q_weight_1d, Q_1d * sizeof(q_weight_1d[0]));
1357   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->interp_1d));
1358   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->grad_1d));
1359   if (interp_1d) memcpy((*basis)->interp_1d, interp_1d, Q_1d * P_1d * sizeof(interp_1d[0]));
1360   if (grad_1d) memcpy((*basis)->grad_1d, grad_1d, Q_1d * P_1d * sizeof(grad_1d[0]));
1361   CeedCall(ceed->BasisCreateTensorH1(dim, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, *basis));
1362   return CEED_ERROR_SUCCESS;
1363 }
1364 
1365 /**
1366   @brief Create a tensor-product \f$H^1\f$ Lagrange basis
1367 
1368   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1369   @param[in]  dim       Topological dimension of element
1370   @param[in]  num_comp  Number of field components (1 for scalar fields)
1371   @param[in]  P         Number of Gauss-Lobatto nodes in one dimension.
1372                           The polynomial degree of the resulting `Q_k` element is `k = P - 1`.
1373   @param[in]  Q         Number of quadrature points in one dimension.
1374   @param[in]  quad_mode Distribution of the `Q` quadrature points (affects order of accuracy for the quadrature)
1375   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1376 
1377   @return An error code: 0 - success, otherwise - failure
1378 
1379   @ref User
1380 **/
1381 int CeedBasisCreateTensorH1Lagrange(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P, CeedInt Q, CeedQuadMode quad_mode, CeedBasis *basis) {
1382   // Allocate
1383   int        ierr = CEED_ERROR_SUCCESS;
1384   CeedScalar c1, c2, c3, c4, dx, *nodes, *interp_1d, *grad_1d, *q_ref_1d, *q_weight_1d;
1385 
1386   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1387   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1388   CeedCheck(P > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1389   CeedCheck(Q > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1390 
1391   // Get Nodes and Weights
1392   CeedCall(CeedCalloc(P * Q, &interp_1d));
1393   CeedCall(CeedCalloc(P * Q, &grad_1d));
1394   CeedCall(CeedCalloc(P, &nodes));
1395   CeedCall(CeedCalloc(Q, &q_ref_1d));
1396   CeedCall(CeedCalloc(Q, &q_weight_1d));
1397   if (CeedLobattoQuadrature(P, nodes, NULL) != CEED_ERROR_SUCCESS) goto cleanup;
1398   switch (quad_mode) {
1399     case CEED_GAUSS:
1400       ierr = CeedGaussQuadrature(Q, q_ref_1d, q_weight_1d);
1401       break;
1402     case CEED_GAUSS_LOBATTO:
1403       ierr = CeedLobattoQuadrature(Q, q_ref_1d, q_weight_1d);
1404       break;
1405   }
1406   if (ierr != CEED_ERROR_SUCCESS) goto cleanup;
1407 
1408   // Build B, D matrix
1409   // Fornberg, 1998
1410   for (CeedInt i = 0; i < Q; i++) {
1411     c1                   = 1.0;
1412     c3                   = nodes[0] - q_ref_1d[i];
1413     interp_1d[i * P + 0] = 1.0;
1414     for (CeedInt j = 1; j < P; j++) {
1415       c2 = 1.0;
1416       c4 = c3;
1417       c3 = nodes[j] - q_ref_1d[i];
1418       for (CeedInt k = 0; k < j; k++) {
1419         dx = nodes[j] - nodes[k];
1420         c2 *= dx;
1421         if (k == j - 1) {
1422           grad_1d[i * P + j]   = c1 * (interp_1d[i * P + k] - c4 * grad_1d[i * P + k]) / c2;
1423           interp_1d[i * P + j] = -c1 * c4 * interp_1d[i * P + k] / c2;
1424         }
1425         grad_1d[i * P + k]   = (c3 * grad_1d[i * P + k] - interp_1d[i * P + k]) / dx;
1426         interp_1d[i * P + k] = c3 * interp_1d[i * P + k] / dx;
1427       }
1428       c1 = c2;
1429     }
1430   }
1431   // Pass to CeedBasisCreateTensorH1
1432   CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P, Q, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1433 cleanup:
1434   CeedCall(CeedFree(&interp_1d));
1435   CeedCall(CeedFree(&grad_1d));
1436   CeedCall(CeedFree(&nodes));
1437   CeedCall(CeedFree(&q_ref_1d));
1438   CeedCall(CeedFree(&q_weight_1d));
1439   return CEED_ERROR_SUCCESS;
1440 }
1441 
1442 /**
1443   @brief Create a non tensor-product basis for \f$H^1\f$ discretizations
1444 
1445   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1446   @param[in]  topo      Topology of element, e.g. hypercube, simplex, etc
1447   @param[in]  num_comp  Number of field components (1 for scalar fields)
1448   @param[in]  num_nodes Total number of nodes
1449   @param[in]  num_qpts  Total number of quadrature points
1450   @param[in]  interp    Row-major (`num_qpts * num_nodes`) matrix expressing the values of nodal basis functions at quadrature points
1451   @param[in]  grad      Row-major (`dim * num_qpts * num_nodes`) matrix expressing derivatives of nodal basis functions at quadrature points
1452   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1453   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1454   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1455 
1456   @return An error code: 0 - success, otherwise - failure
1457 
1458   @ref User
1459 **/
1460 int CeedBasisCreateH1(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1461                       const CeedScalar *grad, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1462   CeedInt P = num_nodes, Q = num_qpts, dim = 0;
1463 
1464   if (!ceed->BasisCreateH1) {
1465     Ceed delegate;
1466 
1467     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1468     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateH1");
1469     CeedCall(CeedBasisCreateH1(delegate, topo, num_comp, num_nodes, num_qpts, interp, grad, q_ref, q_weight, basis));
1470     return CEED_ERROR_SUCCESS;
1471   }
1472 
1473   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1474   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1475   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1476 
1477   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1478 
1479   CeedCall(CeedCalloc(1, basis));
1480   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1481   (*basis)->ref_count       = 1;
1482   (*basis)->is_tensor_basis = false;
1483   (*basis)->dim             = dim;
1484   (*basis)->topo            = topo;
1485   (*basis)->num_comp        = num_comp;
1486   (*basis)->P               = P;
1487   (*basis)->Q               = Q;
1488   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1489   CeedCall(CeedCalloc(Q * dim, &(*basis)->q_ref_1d));
1490   CeedCall(CeedCalloc(Q, &(*basis)->q_weight_1d));
1491   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1492   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1493   CeedCall(CeedCalloc(Q * P, &(*basis)->interp));
1494   CeedCall(CeedCalloc(dim * Q * P, &(*basis)->grad));
1495   if (interp) memcpy((*basis)->interp, interp, Q * P * sizeof(interp[0]));
1496   if (grad) memcpy((*basis)->grad, grad, dim * Q * P * sizeof(grad[0]));
1497   CeedCall(ceed->BasisCreateH1(topo, dim, P, Q, interp, grad, q_ref, q_weight, *basis));
1498   return CEED_ERROR_SUCCESS;
1499 }
1500 
1501 /**
1502   @brief Create a non tensor-product basis for \f$H(\mathrm{div})\f$ discretizations
1503 
1504   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1505   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1506   @param[in]  num_comp  Number of components (usually 1 for vectors in H(div) bases)
1507   @param[in]  num_nodes Total number of nodes (DoFs per element)
1508   @param[in]  num_qpts  Total number of quadrature points
1509   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1510   @param[in]  div       Row-major (`num_qpts * num_nodes`) matrix expressing divergence of basis functions at quadrature points
1511   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1512   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1513   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1514 
1515   @return An error code: 0 - success, otherwise - failure
1516 
1517   @ref User
1518 **/
1519 int CeedBasisCreateHdiv(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1520                         const CeedScalar *div, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1521   CeedInt Q = num_qpts, P = num_nodes, dim = 0;
1522 
1523   if (!ceed->BasisCreateHdiv) {
1524     Ceed delegate;
1525 
1526     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1527     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHdiv");
1528     CeedCall(CeedBasisCreateHdiv(delegate, topo, num_comp, num_nodes, num_qpts, interp, div, q_ref, q_weight, basis));
1529     return CEED_ERROR_SUCCESS;
1530   }
1531 
1532   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1533   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1534   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1535 
1536   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1537 
1538   CeedCall(CeedCalloc(1, basis));
1539   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1540   (*basis)->ref_count       = 1;
1541   (*basis)->is_tensor_basis = false;
1542   (*basis)->dim             = dim;
1543   (*basis)->topo            = topo;
1544   (*basis)->num_comp        = num_comp;
1545   (*basis)->P               = P;
1546   (*basis)->Q               = Q;
1547   (*basis)->fe_space        = CEED_FE_SPACE_HDIV;
1548   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1549   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1550   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1551   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1552   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1553   CeedCall(CeedMalloc(Q * P, &(*basis)->div));
1554   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1555   if (div) memcpy((*basis)->div, div, Q * P * sizeof(div[0]));
1556   CeedCall(ceed->BasisCreateHdiv(topo, dim, P, Q, interp, div, q_ref, q_weight, *basis));
1557   return CEED_ERROR_SUCCESS;
1558 }
1559 
1560 /**
1561   @brief Create a non tensor-product basis for \f$H(\mathrm{curl})\f$ discretizations
1562 
1563   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1564   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1565   @param[in]  num_comp  Number of components (usually 1 for vectors in \f$H(\mathrm{curl})\f$ bases)
1566   @param[in]  num_nodes Total number of nodes (DoFs per element)
1567   @param[in]  num_qpts  Total number of quadrature points
1568   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1569   @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
1570   @param[in]  q_ref     Array of length `num_qpts * dim` holding the locations of quadrature points on the reference element
1571   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1572   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1573 
1574   @return An error code: 0 - success, otherwise - failure
1575 
1576   @ref User
1577 **/
1578 int CeedBasisCreateHcurl(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1579                          const CeedScalar *curl, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1580   CeedInt Q = num_qpts, P = num_nodes, dim = 0, curl_comp = 0;
1581 
1582   if (!ceed->BasisCreateHcurl) {
1583     Ceed delegate;
1584 
1585     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1586     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHcurl");
1587     CeedCall(CeedBasisCreateHcurl(delegate, topo, num_comp, num_nodes, num_qpts, interp, curl, q_ref, q_weight, basis));
1588     return CEED_ERROR_SUCCESS;
1589   }
1590 
1591   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1592   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1593   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1594 
1595   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1596   curl_comp = (dim < 3) ? 1 : dim;
1597 
1598   CeedCall(CeedCalloc(1, basis));
1599   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1600   (*basis)->ref_count       = 1;
1601   (*basis)->is_tensor_basis = false;
1602   (*basis)->dim             = dim;
1603   (*basis)->topo            = topo;
1604   (*basis)->num_comp        = num_comp;
1605   (*basis)->P               = P;
1606   (*basis)->Q               = Q;
1607   (*basis)->fe_space        = CEED_FE_SPACE_HCURL;
1608   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1609   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1610   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1611   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1612   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1613   CeedCall(CeedMalloc(curl_comp * Q * P, &(*basis)->curl));
1614   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1615   if (curl) memcpy((*basis)->curl, curl, curl_comp * Q * P * sizeof(curl[0]));
1616   CeedCall(ceed->BasisCreateHcurl(topo, dim, P, Q, interp, curl, q_ref, q_weight, *basis));
1617   return CEED_ERROR_SUCCESS;
1618 }
1619 
1620 /**
1621   @brief Create a `CeedBasis` for projection from the nodes of `basis_from` to the nodes of `basis_to`.
1622 
1623   Only @ref CEED_EVAL_INTERP will be valid for the new basis, `basis_project`.
1624   For \f$H^1\f$ spaces, @ref CEED_EVAL_GRAD will also be valid.
1625   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
1626   The gradient (for the \f$H^1\f$ case) is given by `grad_project = interp_to^+ * grad_from`.
1627 
1628   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
1629 
1630   Note: `basis_project` will have the same number of components as `basis_from`, regardless of the number of components that `basis_to` has.
1631         If `basis_from` has 3 components and `basis_to` has 5 components, then `basis_project` will have 3 components.
1632 
1633   Note: If either `basis_from` or `basis_to` are non-tensor, then `basis_project` will also be non-tensor
1634 
1635   @param[in]  basis_from    `CeedBasis` to prolong from
1636   @param[in]  basis_to      `CeedBasis` to prolong to
1637   @param[out] basis_project Address of the variable where the newly created `CeedBasis` will be stored
1638 
1639   @return An error code: 0 - success, otherwise - failure
1640 
1641   @ref User
1642 **/
1643 int CeedBasisCreateProjection(CeedBasis basis_from, CeedBasis basis_to, CeedBasis *basis_project) {
1644   Ceed        ceed;
1645   bool        create_tensor;
1646   CeedInt     dim, num_comp;
1647   CeedScalar *interp_project, *grad_project;
1648 
1649   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
1650 
1651   // Create projection matrix
1652   CeedCall(CeedBasisCreateProjectionMatrices(basis_from, basis_to, &interp_project, &grad_project));
1653 
1654   // Build basis
1655   {
1656     bool is_tensor_to, is_tensor_from;
1657 
1658     CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
1659     CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
1660     create_tensor = is_tensor_from && is_tensor_to;
1661   }
1662   CeedCall(CeedBasisGetDimension(basis_to, &dim));
1663   CeedCall(CeedBasisGetNumComponents(basis_from, &num_comp));
1664   if (create_tensor) {
1665     CeedInt P_1d_to, P_1d_from;
1666 
1667     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_1d_from));
1668     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_1d_to));
1669     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d_from, P_1d_to, interp_project, grad_project, NULL, NULL, basis_project));
1670   } else {
1671     // Even if basis_to and basis_from are not H1, the resulting basis is H1 for interpolation to work
1672     CeedInt          num_nodes_to, num_nodes_from;
1673     CeedElemTopology topo;
1674 
1675     CeedCall(CeedBasisGetTopology(basis_from, &topo));
1676     CeedCall(CeedBasisGetNumNodes(basis_from, &num_nodes_from));
1677     CeedCall(CeedBasisGetNumNodes(basis_to, &num_nodes_to));
1678     CeedCall(CeedBasisCreateH1(ceed, topo, num_comp, num_nodes_from, num_nodes_to, interp_project, grad_project, NULL, NULL, basis_project));
1679   }
1680 
1681   // Cleanup
1682   CeedCall(CeedFree(&interp_project));
1683   CeedCall(CeedFree(&grad_project));
1684   return CEED_ERROR_SUCCESS;
1685 }
1686 
1687 /**
1688   @brief Copy the pointer to a `CeedBasis`.
1689 
1690   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`.
1691         This `CeedBasis` will be destroyed if `*basis_copy` is the only reference to this `CeedBasis`.
1692 
1693   @param[in]     basis      `CeedBasis` to copy reference to
1694   @param[in,out] basis_copy Variable to store copied reference
1695 
1696   @return An error code: 0 - success, otherwise - failure
1697 
1698   @ref User
1699 **/
1700 int CeedBasisReferenceCopy(CeedBasis basis, CeedBasis *basis_copy) {
1701   if (basis != CEED_BASIS_NONE) CeedCall(CeedBasisReference(basis));
1702   CeedCall(CeedBasisDestroy(basis_copy));
1703   *basis_copy = basis;
1704   return CEED_ERROR_SUCCESS;
1705 }
1706 
1707 /**
1708   @brief View a `CeedBasis`
1709 
1710   @param[in] basis  `CeedBasis` to view
1711   @param[in] stream Stream to view to, e.g., `stdout`
1712 
1713   @return An error code: 0 - success, otherwise - failure
1714 
1715   @ref User
1716 **/
1717 int CeedBasisView(CeedBasis basis, FILE *stream) {
1718   bool             is_tensor_basis;
1719   CeedElemTopology topo;
1720   CeedFESpace      fe_space;
1721 
1722   // Basis data
1723   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
1724   CeedCall(CeedBasisGetTopology(basis, &topo));
1725   CeedCall(CeedBasisGetFESpace(basis, &fe_space));
1726 
1727   // Print FE space and element topology of the basis
1728   fprintf(stream, "CeedBasis in a %s on a %s element\n", CeedFESpaces[fe_space], CeedElemTopologies[topo]);
1729   if (is_tensor_basis) {
1730     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P_1d, basis->Q_1d);
1731   } else {
1732     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P, basis->Q);
1733   }
1734   fprintf(stream, "  dimension: %" CeedInt_FMT "\n  field components: %" CeedInt_FMT "\n", basis->dim, basis->num_comp);
1735   // Print quadrature data, interpolation/gradient/divergence/curl of the basis
1736   if (is_tensor_basis) {  // tensor basis
1737     CeedInt           P_1d, Q_1d;
1738     const CeedScalar *q_ref_1d, *q_weight_1d, *interp_1d, *grad_1d;
1739 
1740     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
1741     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
1742     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
1743     CeedCall(CeedBasisGetQWeights(basis, &q_weight_1d));
1744     CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
1745     CeedCall(CeedBasisGetGrad1D(basis, &grad_1d));
1746 
1747     CeedCall(CeedScalarView("qref1d", "\t% 12.8f", 1, Q_1d, q_ref_1d, stream));
1748     CeedCall(CeedScalarView("qweight1d", "\t% 12.8f", 1, Q_1d, q_weight_1d, stream));
1749     CeedCall(CeedScalarView("interp1d", "\t% 12.8f", Q_1d, P_1d, interp_1d, stream));
1750     CeedCall(CeedScalarView("grad1d", "\t% 12.8f", Q_1d, P_1d, grad_1d, stream));
1751   } else {  // non-tensor basis
1752     CeedInt           P, Q, dim, q_comp;
1753     const CeedScalar *q_ref, *q_weight, *interp, *grad, *div, *curl;
1754 
1755     CeedCall(CeedBasisGetNumNodes(basis, &P));
1756     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &Q));
1757     CeedCall(CeedBasisGetDimension(basis, &dim));
1758     CeedCall(CeedBasisGetQRef(basis, &q_ref));
1759     CeedCall(CeedBasisGetQWeights(basis, &q_weight));
1760     CeedCall(CeedBasisGetInterp(basis, &interp));
1761     CeedCall(CeedBasisGetGrad(basis, &grad));
1762     CeedCall(CeedBasisGetDiv(basis, &div));
1763     CeedCall(CeedBasisGetCurl(basis, &curl));
1764 
1765     CeedCall(CeedScalarView("qref", "\t% 12.8f", 1, Q * dim, q_ref, stream));
1766     CeedCall(CeedScalarView("qweight", "\t% 12.8f", 1, Q, q_weight, stream));
1767     CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_INTERP, &q_comp));
1768     CeedCall(CeedScalarView("interp", "\t% 12.8f", q_comp * Q, P, interp, stream));
1769     if (grad) {
1770       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_GRAD, &q_comp));
1771       CeedCall(CeedScalarView("grad", "\t% 12.8f", q_comp * Q, P, grad, stream));
1772     }
1773     if (div) {
1774       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_DIV, &q_comp));
1775       CeedCall(CeedScalarView("div", "\t% 12.8f", q_comp * Q, P, div, stream));
1776     }
1777     if (curl) {
1778       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_CURL, &q_comp));
1779       CeedCall(CeedScalarView("curl", "\t% 12.8f", q_comp * Q, P, curl, stream));
1780     }
1781   }
1782   return CEED_ERROR_SUCCESS;
1783 }
1784 
1785 /**
1786   @brief Check input vector dimensions for CeedBasisApply[Add]
1787 
1788   @param[in]  basis     `CeedBasis` to evaluate
1789   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1790                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1791   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1792                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1793   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1794                           @ref CEED_EVAL_INTERP to use interpolated values,
1795                           @ref CEED_EVAL_GRAD to use gradients,
1796                           @ref CEED_EVAL_DIV to use divergence,
1797                           @ref CEED_EVAL_CURL to use curl,
1798                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1799   @param[in]  u         Input `CeedVector`
1800   @param[out] v         Output `CeedVector`
1801 
1802   @return An error code: 0 - success, otherwise - failure
1803 
1804   @ref Developer
1805 **/
1806 static int CeedBasisApplyCheckDims(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1807   CeedInt  dim, num_comp, q_comp, num_nodes, num_qpts;
1808   CeedSize u_length = 0, v_length;
1809   Ceed     ceed;
1810 
1811   CeedCall(CeedBasisGetCeed(basis, &ceed));
1812   CeedCall(CeedBasisGetDimension(basis, &dim));
1813   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1814   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
1815   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1816   CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
1817   CeedCall(CeedVectorGetLength(v, &v_length));
1818   if (u) CeedCall(CeedVectorGetLength(u, &u_length));
1819 
1820   // Check vector lengths to prevent out of bounds issues
1821   bool has_good_dims = true;
1822   switch (eval_mode) {
1823     case CEED_EVAL_NONE:
1824     case CEED_EVAL_INTERP:
1825     case CEED_EVAL_GRAD:
1826     case CEED_EVAL_DIV:
1827     case CEED_EVAL_CURL:
1828       has_good_dims = ((t_mode == CEED_TRANSPOSE && u_length >= (CeedSize)num_elem * (CeedSize)num_comp * (CeedSize)num_qpts * (CeedSize)q_comp &&
1829                         v_length >= (CeedSize)num_elem * (CeedSize)num_comp * (CeedSize)num_nodes) ||
1830                        (t_mode == CEED_NOTRANSPOSE && v_length >= (CeedSize)num_elem * (CeedSize)num_qpts * (CeedSize)num_comp * (CeedSize)q_comp &&
1831                         u_length >= (CeedSize)num_elem * (CeedSize)num_comp * (CeedSize)num_nodes));
1832       break;
1833     case CEED_EVAL_WEIGHT:
1834       has_good_dims = v_length >= (CeedSize)num_elem * (CeedSize)num_qpts;
1835       break;
1836   }
1837   CeedCheck(has_good_dims, ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
1838   return CEED_ERROR_SUCCESS;
1839 }
1840 
1841 /**
1842   @brief Apply basis evaluation from nodes to quadrature points or vice versa
1843 
1844   @param[in]  basis     `CeedBasis` to evaluate
1845   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1846                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1847   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1848                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1849   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1850                           @ref CEED_EVAL_INTERP to use interpolated values,
1851                           @ref CEED_EVAL_GRAD to use gradients,
1852                           @ref CEED_EVAL_DIV to use divergence,
1853                           @ref CEED_EVAL_CURL to use curl,
1854                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1855   @param[in]  u         Input `CeedVector`
1856   @param[out] v         Output `CeedVector`
1857 
1858   @return An error code: 0 - success, otherwise - failure
1859 
1860   @ref User
1861 **/
1862 int CeedBasisApply(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1863   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
1864   CeedCheck(basis->Apply, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not support CeedBasisApply");
1865   CeedCall(basis->Apply(basis, num_elem, t_mode, eval_mode, u, v));
1866   return CEED_ERROR_SUCCESS;
1867 }
1868 
1869 /**
1870   @brief Apply basis evaluation from quadrature points to nodes and sum into target vector
1871 
1872   @param[in]  basis     `CeedBasis` to evaluate
1873   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1874                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1875   @param[in]  t_mode    @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes;
1876                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAdd()`
1877   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1878                           @ref CEED_EVAL_INTERP to use interpolated values,
1879                           @ref CEED_EVAL_GRAD to use gradients,
1880                           @ref CEED_EVAL_DIV to use divergence,
1881                           @ref CEED_EVAL_CURL to use curl,
1882                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1883   @param[in]  u         Input `CeedVector`
1884   @param[out] v         Output `CeedVector` to sum into
1885 
1886   @return An error code: 0 - success, otherwise - failure
1887 
1888   @ref User
1889 **/
1890 int CeedBasisApplyAdd(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1891   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAdd only supports CEED_TRANSPOSE");
1892   CeedCall(CeedBasisApplyCheckDims(basis, num_elem, t_mode, eval_mode, u, v));
1893   CeedCheck(basis->ApplyAdd, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "Backend does not implement CeedBasisApplyAdd");
1894   CeedCall(basis->ApplyAdd(basis, num_elem, t_mode, eval_mode, u, v));
1895   return CEED_ERROR_SUCCESS;
1896 }
1897 
1898 /**
1899   @brief Apply basis evaluation from nodes to arbitrary points
1900 
1901   @param[in]  basis      `CeedBasis` to evaluate
1902   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
1903                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1904   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
1905   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1906                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
1907   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
1908                            @ref CEED_EVAL_GRAD to use gradients,
1909                            @ref CEED_EVAL_WEIGHT to use quadrature weights
1910   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
1911   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
1912   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
1913 
1914   @return An error code: 0 - success, otherwise - failure
1915 
1916   @ref User
1917 **/
1918 int CeedBasisApplyAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
1919                            CeedVector x_ref, CeedVector u, CeedVector v) {
1920   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1921   if (basis->ApplyAtPoints) {
1922     CeedCall(basis->ApplyAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1923   } else {
1924     CeedCall(CeedBasisApplyAtPoints_Core(basis, false, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1925   }
1926   return CEED_ERROR_SUCCESS;
1927 }
1928 
1929 /**
1930   @brief Apply basis evaluation from nodes to arbitrary points and sum into target vector
1931 
1932   @param[in]  basis      `CeedBasis` to evaluate
1933   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
1934                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1935   @param[in]  num_points Array of the number of points to apply the basis evaluation to in each element, size `num_elem`
1936   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1937                            @ref CEED_NOTRANSPOSE is not valid for `CeedBasisApplyAddAtPoints()`
1938   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
1939                            @ref CEED_EVAL_GRAD to use gradients,
1940                            @ref CEED_EVAL_WEIGHT to use quadrature weights
1941   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
1942   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
1943   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
1944 
1945   @return An error code: 0 - success, otherwise - failure
1946 
1947   @ref User
1948 **/
1949 int CeedBasisApplyAddAtPoints(CeedBasis basis, CeedInt num_elem, const CeedInt *num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode,
1950                               CeedVector x_ref, CeedVector u, CeedVector v) {
1951   CeedCheck(t_mode == CEED_TRANSPOSE, CeedBasisReturnCeed(basis), CEED_ERROR_UNSUPPORTED, "CeedBasisApplyAddAtPoints only supports CEED_TRANSPOSE");
1952   CeedCall(CeedBasisApplyAtPointsCheckDims(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1953   if (basis->ApplyAddAtPoints) {
1954     CeedCall(basis->ApplyAddAtPoints(basis, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1955   } else {
1956     CeedCall(CeedBasisApplyAtPoints_Core(basis, true, num_elem, num_points, t_mode, eval_mode, x_ref, u, v));
1957   }
1958   return CEED_ERROR_SUCCESS;
1959 }
1960 
1961 /**
1962   @brief Get the `Ceed` associated with a `CeedBasis`
1963 
1964   @param[in]  basis `CeedBasis`
1965   @param[out] ceed  Variable to store `Ceed`
1966 
1967   @return An error code: 0 - success, otherwise - failure
1968 
1969   @ref Advanced
1970 **/
1971 int CeedBasisGetCeed(CeedBasis basis, Ceed *ceed) {
1972   *ceed = CeedBasisReturnCeed(basis);
1973   return CEED_ERROR_SUCCESS;
1974 }
1975 
1976 /**
1977   @brief Return the `Ceed` associated with a `CeedBasis`
1978 
1979   @param[in]  basis `CeedBasis`
1980 
1981   @return `Ceed` associated with the `basis`
1982 
1983   @ref Advanced
1984 **/
1985 Ceed CeedBasisReturnCeed(CeedBasis basis) { return basis->ceed; }
1986 
1987 /**
1988   @brief Get dimension for given `CeedBasis`
1989 
1990   @param[in]  basis `CeedBasis`
1991   @param[out] dim   Variable to store dimension of basis
1992 
1993   @return An error code: 0 - success, otherwise - failure
1994 
1995   @ref Advanced
1996 **/
1997 int CeedBasisGetDimension(CeedBasis basis, CeedInt *dim) {
1998   *dim = basis->dim;
1999   return CEED_ERROR_SUCCESS;
2000 }
2001 
2002 /**
2003   @brief Get topology for given `CeedBasis`
2004 
2005   @param[in]  basis `CeedBasis`
2006   @param[out] topo  Variable to store topology of basis
2007 
2008   @return An error code: 0 - success, otherwise - failure
2009 
2010   @ref Advanced
2011 **/
2012 int CeedBasisGetTopology(CeedBasis basis, CeedElemTopology *topo) {
2013   *topo = basis->topo;
2014   return CEED_ERROR_SUCCESS;
2015 }
2016 
2017 /**
2018   @brief Get number of components for given `CeedBasis`
2019 
2020   @param[in]  basis    `CeedBasis`
2021   @param[out] num_comp Variable to store number of components
2022 
2023   @return An error code: 0 - success, otherwise - failure
2024 
2025   @ref Advanced
2026 **/
2027 int CeedBasisGetNumComponents(CeedBasis basis, CeedInt *num_comp) {
2028   *num_comp = basis->num_comp;
2029   return CEED_ERROR_SUCCESS;
2030 }
2031 
2032 /**
2033   @brief Get total number of nodes (in `dim` dimensions) of a `CeedBasis`
2034 
2035   @param[in]  basis `CeedBasis`
2036   @param[out] P     Variable to store number of nodes
2037 
2038   @return An error code: 0 - success, otherwise - failure
2039 
2040   @ref Utility
2041 **/
2042 int CeedBasisGetNumNodes(CeedBasis basis, CeedInt *P) {
2043   *P = basis->P;
2044   return CEED_ERROR_SUCCESS;
2045 }
2046 
2047 /**
2048   @brief Get total number of nodes (in 1 dimension) of a `CeedBasis`
2049 
2050   @param[in]  basis `CeedBasis`
2051   @param[out] P_1d  Variable to store number of nodes
2052 
2053   @return An error code: 0 - success, otherwise - failure
2054 
2055   @ref Advanced
2056 **/
2057 int CeedBasisGetNumNodes1D(CeedBasis basis, CeedInt *P_1d) {
2058   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply P_1d for non-tensor CeedBasis");
2059   *P_1d = basis->P_1d;
2060   return CEED_ERROR_SUCCESS;
2061 }
2062 
2063 /**
2064   @brief Get total number of quadrature points (in `dim` dimensions) of a `CeedBasis`
2065 
2066   @param[in]  basis `CeedBasis`
2067   @param[out] Q     Variable to store number of quadrature points
2068 
2069   @return An error code: 0 - success, otherwise - failure
2070 
2071   @ref Utility
2072 **/
2073 int CeedBasisGetNumQuadraturePoints(CeedBasis basis, CeedInt *Q) {
2074   *Q = basis->Q;
2075   return CEED_ERROR_SUCCESS;
2076 }
2077 
2078 /**
2079   @brief Get total number of quadrature points (in 1 dimension) of a `CeedBasis`
2080 
2081   @param[in]  basis `CeedBasis`
2082   @param[out] Q_1d  Variable to store number of quadrature points
2083 
2084   @return An error code: 0 - success, otherwise - failure
2085 
2086   @ref Advanced
2087 **/
2088 int CeedBasisGetNumQuadraturePoints1D(CeedBasis basis, CeedInt *Q_1d) {
2089   CeedCheck(basis->is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "Cannot supply Q_1d for non-tensor CeedBasis");
2090   *Q_1d = basis->Q_1d;
2091   return CEED_ERROR_SUCCESS;
2092 }
2093 
2094 /**
2095   @brief Get reference coordinates of quadrature points (in `dim` dimensions) of a `CeedBasis`
2096 
2097   @param[in]  basis `CeedBasis`
2098   @param[out] q_ref Variable to store reference coordinates of quadrature points
2099 
2100   @return An error code: 0 - success, otherwise - failure
2101 
2102   @ref Advanced
2103 **/
2104 int CeedBasisGetQRef(CeedBasis basis, const CeedScalar **q_ref) {
2105   *q_ref = basis->q_ref_1d;
2106   return CEED_ERROR_SUCCESS;
2107 }
2108 
2109 /**
2110   @brief Get quadrature weights of quadrature points (in `dim` dimensions) of a `CeedBasis`
2111 
2112   @param[in]  basis    `CeedBasis`
2113   @param[out] q_weight Variable to store quadrature weights
2114 
2115   @return An error code: 0 - success, otherwise - failure
2116 
2117   @ref Advanced
2118 **/
2119 int CeedBasisGetQWeights(CeedBasis basis, const CeedScalar **q_weight) {
2120   *q_weight = basis->q_weight_1d;
2121   return CEED_ERROR_SUCCESS;
2122 }
2123 
2124 /**
2125   @brief Get interpolation matrix of a `CeedBasis`
2126 
2127   @param[in]  basis  `CeedBasis`
2128   @param[out] interp Variable to store interpolation matrix
2129 
2130   @return An error code: 0 - success, otherwise - failure
2131 
2132   @ref Advanced
2133 **/
2134 int CeedBasisGetInterp(CeedBasis basis, const CeedScalar **interp) {
2135   if (!basis->interp && basis->is_tensor_basis) {
2136     // Allocate
2137     CeedCall(CeedMalloc(basis->Q * basis->P, &basis->interp));
2138 
2139     // Initialize
2140     for (CeedInt i = 0; i < basis->Q * basis->P; i++) basis->interp[i] = 1.0;
2141 
2142     // Calculate
2143     for (CeedInt d = 0; d < basis->dim; d++) {
2144       for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2145         for (CeedInt node = 0; node < basis->P; node++) {
2146           CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2147           CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2148 
2149           basis->interp[qpt * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2150         }
2151       }
2152     }
2153   }
2154   *interp = basis->interp;
2155   return CEED_ERROR_SUCCESS;
2156 }
2157 
2158 /**
2159   @brief Get 1D interpolation matrix of a tensor product `CeedBasis`
2160 
2161   @param[in]  basis     `CeedBasis`
2162   @param[out] interp_1d Variable to store interpolation matrix
2163 
2164   @return An error code: 0 - success, otherwise - failure
2165 
2166   @ref Backend
2167 **/
2168 int CeedBasisGetInterp1D(CeedBasis basis, const CeedScalar **interp_1d) {
2169   bool is_tensor_basis;
2170 
2171   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2172   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2173   *interp_1d = basis->interp_1d;
2174   return CEED_ERROR_SUCCESS;
2175 }
2176 
2177 /**
2178   @brief Get gradient matrix of a `CeedBasis`
2179 
2180   @param[in]  basis `CeedBasis`
2181   @param[out] grad  Variable to store gradient matrix
2182 
2183   @return An error code: 0 - success, otherwise - failure
2184 
2185   @ref Advanced
2186 **/
2187 int CeedBasisGetGrad(CeedBasis basis, const CeedScalar **grad) {
2188   if (!basis->grad && basis->is_tensor_basis) {
2189     // Allocate
2190     CeedCall(CeedMalloc(basis->dim * basis->Q * basis->P, &basis->grad));
2191 
2192     // Initialize
2193     for (CeedInt i = 0; i < basis->dim * basis->Q * basis->P; i++) basis->grad[i] = 1.0;
2194 
2195     // Calculate
2196     for (CeedInt d = 0; d < basis->dim; d++) {
2197       for (CeedInt i = 0; i < basis->dim; i++) {
2198         for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
2199           for (CeedInt node = 0; node < basis->P; node++) {
2200             CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
2201             CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
2202 
2203             if (i == d) basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->grad_1d[q * basis->P_1d + p];
2204             else basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
2205           }
2206         }
2207       }
2208     }
2209   }
2210   *grad = basis->grad;
2211   return CEED_ERROR_SUCCESS;
2212 }
2213 
2214 /**
2215   @brief Get 1D gradient matrix of a tensor product `CeedBasis`
2216 
2217   @param[in]  basis   `CeedBasis`
2218   @param[out] grad_1d Variable to store gradient matrix
2219 
2220   @return An error code: 0 - success, otherwise - failure
2221 
2222   @ref Advanced
2223 **/
2224 int CeedBasisGetGrad1D(CeedBasis basis, const CeedScalar **grad_1d) {
2225   bool is_tensor_basis;
2226 
2227   CeedCall(CeedBasisIsTensor(basis, &is_tensor_basis));
2228   CeedCheck(is_tensor_basis, CeedBasisReturnCeed(basis), CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
2229   *grad_1d = basis->grad_1d;
2230   return CEED_ERROR_SUCCESS;
2231 }
2232 
2233 /**
2234   @brief Get divergence matrix of a `CeedBasis`
2235 
2236   @param[in]  basis `CeedBasis`
2237   @param[out] div   Variable to store divergence matrix
2238 
2239   @return An error code: 0 - success, otherwise - failure
2240 
2241   @ref Advanced
2242 **/
2243 int CeedBasisGetDiv(CeedBasis basis, const CeedScalar **div) {
2244   *div = basis->div;
2245   return CEED_ERROR_SUCCESS;
2246 }
2247 
2248 /**
2249   @brief Get curl matrix of a `CeedBasis`
2250 
2251   @param[in]  basis `CeedBasis`
2252   @param[out] curl  Variable to store curl matrix
2253 
2254   @return An error code: 0 - success, otherwise - failure
2255 
2256   @ref Advanced
2257 **/
2258 int CeedBasisGetCurl(CeedBasis basis, const CeedScalar **curl) {
2259   *curl = basis->curl;
2260   return CEED_ERROR_SUCCESS;
2261 }
2262 
2263 /**
2264   @brief Destroy a @ref  CeedBasis
2265 
2266   @param[in,out] basis `CeedBasis` to destroy
2267 
2268   @return An error code: 0 - success, otherwise - failure
2269 
2270   @ref User
2271 **/
2272 int CeedBasisDestroy(CeedBasis *basis) {
2273   if (!*basis || *basis == CEED_BASIS_NONE || --(*basis)->ref_count > 0) {
2274     *basis = NULL;
2275     return CEED_ERROR_SUCCESS;
2276   }
2277   if ((*basis)->Destroy) CeedCall((*basis)->Destroy(*basis));
2278   CeedCall(CeedTensorContractDestroy(&(*basis)->contract));
2279   CeedCall(CeedFree(&(*basis)->q_ref_1d));
2280   CeedCall(CeedFree(&(*basis)->q_weight_1d));
2281   CeedCall(CeedFree(&(*basis)->interp));
2282   CeedCall(CeedFree(&(*basis)->interp_1d));
2283   CeedCall(CeedFree(&(*basis)->grad));
2284   CeedCall(CeedFree(&(*basis)->grad_1d));
2285   CeedCall(CeedFree(&(*basis)->div));
2286   CeedCall(CeedFree(&(*basis)->curl));
2287   CeedCall(CeedVectorDestroy(&(*basis)->vec_chebyshev));
2288   CeedCall(CeedBasisDestroy(&(*basis)->basis_chebyshev));
2289   CeedCall(CeedDestroy(&(*basis)->ceed));
2290   CeedCall(CeedFree(basis));
2291   return CEED_ERROR_SUCCESS;
2292 }
2293 
2294 /**
2295   @brief Construct a Gauss-Legendre quadrature
2296 
2297   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-1` exactly)
2298   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2299   @param[out] q_weight_1d Array of length `Q` to hold the weights
2300 
2301   @return An error code: 0 - success, otherwise - failure
2302 
2303   @ref Utility
2304 **/
2305 int CeedGaussQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2306   CeedScalar P0, P1, P2, dP2, xi, wi, PI = 4.0 * atan(1.0);
2307 
2308   // Build q_ref_1d, q_weight_1d
2309   for (CeedInt i = 0; i <= Q / 2; i++) {
2310     // Guess
2311     xi = cos(PI * (CeedScalar)(2 * i + 1) / ((CeedScalar)(2 * Q)));
2312     // Pn(xi)
2313     P0 = 1.0;
2314     P1 = xi;
2315     P2 = 0.0;
2316     for (CeedInt j = 2; j <= Q; j++) {
2317       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2318       P0 = P1;
2319       P1 = P2;
2320     }
2321     // First Newton Step
2322     dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2323     xi  = xi - P2 / dP2;
2324     // Newton to convergence
2325     for (CeedInt k = 0; k < 100 && fabs(P2) > 10 * CEED_EPSILON; k++) {
2326       P0 = 1.0;
2327       P1 = xi;
2328       for (CeedInt j = 2; j <= Q; j++) {
2329         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2330         P0 = P1;
2331         P1 = P2;
2332       }
2333       dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2334       xi  = xi - P2 / dP2;
2335     }
2336     // Save xi, wi
2337     wi                     = 2.0 / ((1.0 - xi * xi) * dP2 * dP2);
2338     q_weight_1d[i]         = wi;
2339     q_weight_1d[Q - 1 - i] = wi;
2340     q_ref_1d[i]            = -xi;
2341     q_ref_1d[Q - 1 - i]    = xi;
2342   }
2343   return CEED_ERROR_SUCCESS;
2344 }
2345 
2346 /**
2347   @brief Construct a Gauss-Legendre-Lobatto quadrature
2348 
2349   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-3` exactly)
2350   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2351   @param[out] q_weight_1d Array of length `Q` to hold the weights
2352 
2353   @return An error code: 0 - success, otherwise - failure
2354 
2355   @ref Utility
2356 **/
2357 int CeedLobattoQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2358   CeedScalar P0, P1, P2, dP2, d2P2, xi, wi, PI = 4.0 * atan(1.0);
2359 
2360   // Build q_ref_1d, q_weight_1d
2361   // Set endpoints
2362   CeedCheck(Q > 1, NULL, CEED_ERROR_DIMENSION, "Cannot create Lobatto quadrature with Q=%" CeedInt_FMT " < 2 points", Q);
2363   wi = 2.0 / ((CeedScalar)(Q * (Q - 1)));
2364   if (q_weight_1d) {
2365     q_weight_1d[0]     = wi;
2366     q_weight_1d[Q - 1] = wi;
2367   }
2368   q_ref_1d[0]     = -1.0;
2369   q_ref_1d[Q - 1] = 1.0;
2370   // Interior
2371   for (CeedInt i = 1; i <= (Q - 1) / 2; i++) {
2372     // Guess
2373     xi = cos(PI * (CeedScalar)(i) / (CeedScalar)(Q - 1));
2374     // Pn(xi)
2375     P0 = 1.0;
2376     P1 = xi;
2377     P2 = 0.0;
2378     for (CeedInt j = 2; j < Q; j++) {
2379       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2380       P0 = P1;
2381       P1 = P2;
2382     }
2383     // First Newton step
2384     dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2385     d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2386     xi   = xi - dP2 / d2P2;
2387     // Newton to convergence
2388     for (CeedInt k = 0; k < 100 && fabs(dP2) > 10 * CEED_EPSILON; k++) {
2389       P0 = 1.0;
2390       P1 = xi;
2391       for (CeedInt j = 2; j < Q; j++) {
2392         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2393         P0 = P1;
2394         P1 = P2;
2395       }
2396       dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2397       d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2398       xi   = xi - dP2 / d2P2;
2399     }
2400     // Save xi, wi
2401     wi = 2.0 / (((CeedScalar)(Q * (Q - 1))) * P2 * P2);
2402     if (q_weight_1d) {
2403       q_weight_1d[i]         = wi;
2404       q_weight_1d[Q - 1 - i] = wi;
2405     }
2406     q_ref_1d[i]         = -xi;
2407     q_ref_1d[Q - 1 - i] = xi;
2408   }
2409   return CEED_ERROR_SUCCESS;
2410 }
2411 
2412 /// @}
2413