xref: /libCEED/interface/ceed-basis.c (revision edfbf3a6ecdc64ed3c23c2b517cc2ccd94396914)
1 // Copyright (c) 2017-2022, 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_collocated;
21 /// @endcond
22 
23 /// @addtogroup CeedBasisUser
24 /// @{
25 
26 /// Indicate that the quadrature points are collocated with the nodes
27 const CeedBasis CEED_BASIS_COLLOCATED = &ceed_basis_collocated;
28 
29 /// @}
30 
31 /// ----------------------------------------------------------------------------
32 /// CeedBasis Library Internal Functions
33 /// ----------------------------------------------------------------------------
34 /// @addtogroup CeedBasisDeveloper
35 /// @{
36 
37 /**
38   @brief Compute Householder reflection
39 
40   Computes A = (I - b v v^T) A, where A is an mxn matrix indexed as A[i*row + j*col]
41 
42   @param[in,out] A   Matrix to apply Householder reflection to, in place
43   @param[in]     v   Householder vector
44   @param[in]     b   Scaling factor
45   @param[in]     m   Number of rows in A
46   @param[in]     n   Number of columns in A
47   @param[in]     row Row stride
48   @param[in]     col Col stride
49 
50   @return An error code: 0 - success, otherwise - failure
51 
52   @ref Developer
53 **/
54 static int CeedHouseholderReflect(CeedScalar *A, const CeedScalar *v, CeedScalar b, CeedInt m, CeedInt n, CeedInt row, CeedInt col) {
55   for (CeedInt j = 0; j < n; j++) {
56     CeedScalar w = A[0 * row + j * col];
57     for (CeedInt i = 1; i < m; i++) w += v[i] * A[i * row + j * col];
58     A[0 * row + j * col] -= b * w;
59     for (CeedInt i = 1; i < m; i++) A[i * row + j * col] -= b * w * v[i];
60   }
61   return CEED_ERROR_SUCCESS;
62 }
63 
64 /**
65   @brief Compute Givens rotation
66 
67   Computes A = G A (or G^T A in transpose mode), where A is an mxn matrix indexed as A[i*n + j*m]
68 
69   @param[in,out] A      Row major matrix to apply Givens rotation to, in place
70   @param[in]     c      Cosine factor
71   @param[in]     s      Sine factor
72   @param[in]     t_mode @ref CEED_NOTRANSPOSE to rotate the basis counter-clockwise, which has the effect of rotating columns of A clockwise;
73                           @ref CEED_TRANSPOSE for the opposite rotation
74   @param[in]     i      First row/column to apply rotation
75   @param[in]     k      Second row/column to apply rotation
76   @param[in]     m      Number of rows in A
77   @param[in]     n      Number of columns in A
78 
79   @return An error code: 0 - success, otherwise - failure
80 
81   @ref Developer
82 **/
83 static int CeedGivensRotation(CeedScalar *A, CeedScalar c, CeedScalar s, CeedTransposeMode t_mode, CeedInt i, CeedInt k, CeedInt m, CeedInt n) {
84   CeedInt stride_j = 1, stride_ik = m, num_its = n;
85   if (t_mode == CEED_NOTRANSPOSE) {
86     stride_j  = n;
87     stride_ik = 1;
88     num_its   = m;
89   }
90 
91   // Apply rotation
92   for (CeedInt j = 0; j < num_its; j++) {
93     CeedScalar tau1 = A[i * stride_ik + j * stride_j], tau2 = A[k * stride_ik + j * stride_j];
94     A[i * stride_ik + j * stride_j] = c * tau1 - s * tau2;
95     A[k * stride_ik + j * stride_j] = s * tau1 + c * tau2;
96   }
97   return CEED_ERROR_SUCCESS;
98 }
99 
100 /**
101   @brief View an array stored in a CeedBasis
102 
103   @param[in] name   Name of array
104   @param[in] fp_fmt Printing format
105   @param[in] m      Number of rows in array
106   @param[in] n      Number of columns in array
107   @param[in] a      Array to be viewed
108   @param[in] stream Stream to view to, e.g., stdout
109 
110   @return An error code: 0 - success, otherwise - failure
111 
112   @ref Developer
113 **/
114 static int CeedScalarView(const char *name, const char *fp_fmt, CeedInt m, CeedInt n, const CeedScalar *a, FILE *stream) {
115   for (CeedInt i = 0; i < m; i++) {
116     if (m > 1) fprintf(stream, "%12s[%" CeedInt_FMT "]:", name, i);
117     else fprintf(stream, "%12s:", name);
118     for (CeedInt j = 0; j < n; j++) fprintf(stream, fp_fmt, fabs(a[i * n + j]) > 1E-14 ? a[i * n + j] : 0);
119     fputs("\n", stream);
120   }
121   return CEED_ERROR_SUCCESS;
122 }
123 
124 /**
125   @brief Create the interpolation and gradient matrices for projection from the nodes of `basis_from` to the nodes of `basis_to`.
126 
127   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
128   The gradient is given by `grad_project = interp_to^+ * grad_from`, and is only computed for H^1 spaces otherwise it should not be used.
129 
130   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
131 
132   @param[in]  basis_from     CeedBasis to project from
133   @param[in]  basis_to       CeedBasis to project to
134   @param[out] interp_project Address of the variable where the newly created interpolation matrix will be stored.
135   @param[out] grad_project   Address of the variable where the newly created gradient matrix will be stored.
136 
137   @return An error code: 0 - success, otherwise - failure
138 
139   @ref Developer
140 **/
141 static int CeedBasisCreateProjectionMatrices(CeedBasis basis_from, CeedBasis basis_to, CeedScalar **interp_project, CeedScalar **grad_project) {
142   Ceed ceed;
143   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
144 
145   // Check for compatible quadrature spaces
146   CeedInt Q_to, Q_from;
147   CeedCall(CeedBasisGetNumQuadraturePoints(basis_to, &Q_to));
148   CeedCall(CeedBasisGetNumQuadraturePoints(basis_from, &Q_from));
149   CeedCheck(Q_to == Q_from, ceed, CEED_ERROR_DIMENSION, "Bases must have compatible quadrature spaces");
150 
151   // Check for matching tensor or non-tensor
152   CeedInt P_to, P_from, Q = Q_to;
153   bool    is_tensor_to, is_tensor_from;
154   CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
155   CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
156   CeedCheck(is_tensor_to == is_tensor_from, ceed, CEED_ERROR_MINOR, "Bases must both be tensor or non-tensor");
157   if (is_tensor_to) {
158     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_to));
159     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_from));
160     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis_from, &Q));
161   } else {
162     CeedCall(CeedBasisGetNumNodes(basis_to, &P_to));
163     CeedCall(CeedBasisGetNumNodes(basis_from, &P_from));
164   }
165 
166   // Check for matching FE space
167   CeedFESpace fe_space_to, fe_space_from;
168   CeedCall(CeedBasisGetFESpace(basis_to, &fe_space_to));
169   CeedCall(CeedBasisGetFESpace(basis_from, &fe_space_from));
170   CeedCheck(fe_space_to == fe_space_from, ceed, CEED_ERROR_MINOR, "Bases must both be the same FE space type");
171 
172   // Get source matrices
173   CeedInt           dim, q_comp = 1;
174   const CeedScalar *interp_to_source = NULL, *interp_from_source = NULL;
175   CeedScalar       *interp_to, *interp_from, *tau;
176   CeedCall(CeedBasisGetDimension(basis_to, &dim));
177   if (is_tensor_to) {
178     CeedCall(CeedBasisGetInterp1D(basis_to, &interp_to_source));
179     CeedCall(CeedBasisGetInterp1D(basis_from, &interp_from_source));
180   } else {
181     CeedCall(CeedBasisGetNumQuadratureComponents(basis_from, CEED_EVAL_INTERP, &q_comp));
182     CeedCall(CeedBasisGetInterp(basis_to, &interp_to_source));
183     CeedCall(CeedBasisGetInterp(basis_from, &interp_from_source));
184   }
185   CeedCall(CeedMalloc(Q * P_from * q_comp, &interp_from));
186   CeedCall(CeedMalloc(Q * P_to * q_comp, &interp_to));
187   CeedCall(CeedCalloc(P_to * P_from, interp_project));
188   CeedCall(CeedMalloc(Q * q_comp, &tau));
189 
190   // `grad_project = interp_to^+ * grad_from` is computed for the H^1 space case so the
191   // projection basis will have a gradient operation (allocated even if not H^1 for the
192   // basis construction later on)
193   const CeedScalar *grad_from_source = NULL;
194   if (fe_space_to == CEED_FE_SPACE_H1) {
195     if (is_tensor_to) {
196       CeedCall(CeedBasisGetGrad1D(basis_from, &grad_from_source));
197     } else {
198       CeedCall(CeedBasisGetGrad(basis_from, &grad_from_source));
199     }
200   }
201   CeedCall(CeedCalloc(P_to * P_from * (is_tensor_to ? 1 : dim), grad_project));
202 
203   // QR Factorization, interp_to = Q R
204   memcpy(interp_to, interp_to_source, Q * P_to * q_comp * sizeof(interp_to_source[0]));
205   CeedCall(CeedQRFactorization(ceed, interp_to, tau, Q * q_comp, P_to));
206 
207   // Build matrices
208   CeedInt     num_matrices = 1 + (fe_space_to == CEED_FE_SPACE_H1) * (is_tensor_to ? 1 : dim);
209   CeedScalar *input_from[num_matrices], *output_project[num_matrices];
210   input_from[0]     = (CeedScalar *)interp_from_source;
211   output_project[0] = *interp_project;
212   for (CeedInt m = 1; m < num_matrices; m++) {
213     input_from[m]     = (CeedScalar *)&grad_from_source[(m - 1) * Q * P_from];
214     output_project[m] = &((*grad_project)[(m - 1) * P_to * P_from]);
215   }
216   for (CeedInt m = 0; m < num_matrices; m++) {
217     // Apply Q^T, interp_from = Q^T interp_from
218     memcpy(interp_from, input_from[m], Q * P_from * q_comp * sizeof(input_from[m][0]));
219     CeedCall(CeedHouseholderApplyQ(interp_from, interp_to, tau, CEED_TRANSPOSE, Q * q_comp, P_from, P_to, P_from, 1));
220 
221     // Apply Rinv, output_project = Rinv interp_from
222     for (CeedInt j = 0; j < P_from; j++) {  // Column j
223       output_project[m][j + P_from * (P_to - 1)] = interp_from[j + P_from * (P_to - 1)] / interp_to[P_to * P_to - 1];
224       for (CeedInt i = P_to - 2; i >= 0; i--) {  // Row i
225         output_project[m][j + P_from * i] = interp_from[j + P_from * i];
226         for (CeedInt k = i + 1; k < P_to; k++) {
227           output_project[m][j + P_from * i] -= interp_to[k + P_to * i] * output_project[m][j + P_from * k];
228         }
229         output_project[m][j + P_from * i] /= interp_to[i + P_to * i];
230       }
231     }
232   }
233 
234   // Cleanup
235   CeedCall(CeedFree(&tau));
236   CeedCall(CeedFree(&interp_to));
237   CeedCall(CeedFree(&interp_from));
238 
239   return CEED_ERROR_SUCCESS;
240 }
241 
242 /// @}
243 
244 /// ----------------------------------------------------------------------------
245 /// Ceed Backend API
246 /// ----------------------------------------------------------------------------
247 /// @addtogroup CeedBasisBackend
248 /// @{
249 
250 /**
251   @brief Return collocated grad matrix
252 
253   @param[in]  basis         CeedBasis
254   @param[out] collo_grad_1d Row-major (Q_1d * Q_1d) matrix expressing derivatives of basis functions at quadrature points
255 
256   @return An error code: 0 - success, otherwise - failure
257 
258   @ref Backend
259 **/
260 int CeedBasisGetCollocatedGrad(CeedBasis basis, CeedScalar *collo_grad_1d) {
261   Ceed        ceed;
262   CeedInt     P_1d = (basis)->P_1d, Q_1d = (basis)->Q_1d;
263   CeedScalar *interp_1d, *grad_1d, *tau;
264 
265   CeedCall(CeedMalloc(Q_1d * P_1d, &interp_1d));
266   CeedCall(CeedMalloc(Q_1d * P_1d, &grad_1d));
267   CeedCall(CeedMalloc(Q_1d, &tau));
268   memcpy(interp_1d, (basis)->interp_1d, Q_1d * P_1d * sizeof(basis)->interp_1d[0]);
269   memcpy(grad_1d, (basis)->grad_1d, Q_1d * P_1d * sizeof(basis)->interp_1d[0]);
270 
271   // QR Factorization, interp_1d = Q R
272   CeedCall(CeedBasisGetCeed(basis, &ceed));
273   CeedCall(CeedQRFactorization(ceed, interp_1d, tau, Q_1d, P_1d));
274   // Note: This function is for backend use, so all errors are terminal and we do not need to clean up memory on failure.
275 
276   // Apply R_inv, collo_grad_1d = grad_1d R_inv
277   for (CeedInt i = 0; i < Q_1d; i++) {  // Row i
278     collo_grad_1d[Q_1d * i] = grad_1d[P_1d * i] / interp_1d[0];
279     for (CeedInt j = 1; j < P_1d; j++) {  // Column j
280       collo_grad_1d[j + Q_1d * i] = grad_1d[j + P_1d * i];
281       for (CeedInt k = 0; k < j; k++) collo_grad_1d[j + Q_1d * i] -= interp_1d[j + P_1d * k] * collo_grad_1d[k + Q_1d * i];
282       collo_grad_1d[j + Q_1d * i] /= interp_1d[j + P_1d * j];
283     }
284     for (CeedInt j = P_1d; j < Q_1d; j++) collo_grad_1d[j + Q_1d * i] = 0;
285   }
286 
287   // Apply Q^T, collo_grad_1d = collo_grad_1d Q^T
288   CeedCall(CeedHouseholderApplyQ(collo_grad_1d, interp_1d, tau, CEED_NOTRANSPOSE, Q_1d, Q_1d, P_1d, 1, Q_1d));
289 
290   CeedCall(CeedFree(&interp_1d));
291   CeedCall(CeedFree(&grad_1d));
292   CeedCall(CeedFree(&tau));
293   return CEED_ERROR_SUCCESS;
294 }
295 
296 /**
297   @brief Get tensor status for given CeedBasis
298 
299   @param[in]  basis     CeedBasis
300   @param[out] is_tensor Variable to store tensor status
301 
302   @return An error code: 0 - success, otherwise - failure
303 
304   @ref Backend
305 **/
306 int CeedBasisIsTensor(CeedBasis basis, bool *is_tensor) {
307   *is_tensor = basis->is_tensor_basis;
308   return CEED_ERROR_SUCCESS;
309 }
310 
311 /**
312   @brief Get backend data of a CeedBasis
313 
314   @param[in]  basis CeedBasis
315   @param[out] data  Variable to store data
316 
317   @return An error code: 0 - success, otherwise - failure
318 
319   @ref Backend
320 **/
321 int CeedBasisGetData(CeedBasis basis, void *data) {
322   *(void **)data = basis->data;
323   return CEED_ERROR_SUCCESS;
324 }
325 
326 /**
327   @brief Set backend data of a CeedBasis
328 
329   @param[in,out] basis  CeedBasis
330   @param[in]     data   Data to set
331 
332   @return An error code: 0 - success, otherwise - failure
333 
334   @ref Backend
335 **/
336 int CeedBasisSetData(CeedBasis basis, void *data) {
337   basis->data = data;
338   return CEED_ERROR_SUCCESS;
339 }
340 
341 /**
342   @brief Increment the reference counter for a CeedBasis
343 
344   @param[in,out] basis Basis to increment the reference counter
345 
346   @return An error code: 0 - success, otherwise - failure
347 
348   @ref Backend
349 **/
350 int CeedBasisReference(CeedBasis basis) {
351   basis->ref_count++;
352   return CEED_ERROR_SUCCESS;
353 }
354 
355 /**
356   @brief Get number of Q-vector components for given CeedBasis
357 
358   @param[in]  basis  CeedBasis
359   @param[in]  eval_mode \ref CEED_EVAL_INTERP to use interpolated values,
360                           \ref CEED_EVAL_GRAD to use gradients,
361                           \ref CEED_EVAL_DIV to use divergence,
362                           \ref CEED_EVAL_CURL to use curl.
363   @param[out] q_comp Variable to store number of Q-vector components of basis
364 
365   @return An error code: 0 - success, otherwise - failure
366 
367   @ref Backend
368 **/
369 int CeedBasisGetNumQuadratureComponents(CeedBasis basis, CeedEvalMode eval_mode, CeedInt *q_comp) {
370   switch (eval_mode) {
371     case CEED_EVAL_INTERP:
372       *q_comp = (basis->fe_space == CEED_FE_SPACE_H1) ? 1 : basis->dim;
373       break;
374     case CEED_EVAL_GRAD:
375       *q_comp = basis->dim;
376       break;
377     case CEED_EVAL_DIV:
378       *q_comp = 1;
379       break;
380     case CEED_EVAL_CURL:
381       *q_comp = (basis->dim < 3) ? 1 : basis->dim;
382       break;
383     case CEED_EVAL_NONE:
384     case CEED_EVAL_WEIGHT:
385       *q_comp = 1;
386       break;
387   }
388   return CEED_ERROR_SUCCESS;
389 }
390 
391 /**
392   @brief Estimate number of FLOPs required to apply CeedBasis in t_mode and eval_mode
393 
394   @param[in]  basis     Basis to estimate FLOPs for
395   @param[in]  t_mode    Apply basis or transpose
396   @param[in]  eval_mode Basis evaluation mode
397   @param[out] flops     Address of variable to hold FLOPs estimate
398 
399   @ref Backend
400 **/
401 int CeedBasisGetFlopsEstimate(CeedBasis basis, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedSize *flops) {
402   bool is_tensor;
403 
404   CeedCall(CeedBasisIsTensor(basis, &is_tensor));
405   if (is_tensor) {
406     CeedInt dim, num_comp, P_1d, Q_1d;
407     CeedCall(CeedBasisGetDimension(basis, &dim));
408     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
409     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
410     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
411     if (t_mode == CEED_TRANSPOSE) {
412       P_1d = Q_1d;
413       Q_1d = P_1d;
414     }
415     CeedInt tensor_flops = 0, pre = num_comp * CeedIntPow(P_1d, dim - 1), post = 1;
416     for (CeedInt d = 0; d < dim; d++) {
417       tensor_flops += 2 * pre * P_1d * post * Q_1d;
418       pre /= P_1d;
419       post *= Q_1d;
420     }
421     switch (eval_mode) {
422       case CEED_EVAL_NONE:
423         *flops = 0;
424         break;
425       case CEED_EVAL_INTERP:
426         *flops = tensor_flops;
427         break;
428       case CEED_EVAL_GRAD:
429         *flops = tensor_flops * 2;
430         break;
431       case CEED_EVAL_DIV:
432       case CEED_EVAL_CURL:
433         // LCOV_EXCL_START
434         return CeedError(basis->ceed, CEED_ERROR_INCOMPATIBLE, "Tensor basis evaluation for %s not supported", CeedEvalModes[eval_mode]);
435         break;
436       // LCOV_EXCL_STOP
437       case CEED_EVAL_WEIGHT:
438         *flops = dim * CeedIntPow(Q_1d, dim);
439         break;
440     }
441   } else {
442     CeedInt dim, num_comp, q_comp, num_nodes, num_qpts;
443     CeedCall(CeedBasisGetDimension(basis, &dim));
444     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
445     CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
446     CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
447     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
448     switch (eval_mode) {
449       case CEED_EVAL_NONE:
450         *flops = 0;
451         break;
452       case CEED_EVAL_INTERP:
453       case CEED_EVAL_GRAD:
454       case CEED_EVAL_DIV:
455       case CEED_EVAL_CURL:
456         *flops = num_nodes * num_qpts * num_comp * q_comp;
457         break;
458       case CEED_EVAL_WEIGHT:
459         *flops = 0;
460         break;
461     }
462   }
463 
464   return CEED_ERROR_SUCCESS;
465 }
466 
467 /**
468   @brief Get CeedFESpace for a CeedBasis
469 
470   @param[in]  basis     CeedBasis
471   @param[out] fe_space  Variable to store CeedFESpace
472 
473   @return An error code: 0 - success, otherwise - failure
474 
475   @ref Backend
476 **/
477 int CeedBasisGetFESpace(CeedBasis basis, CeedFESpace *fe_space) {
478   *fe_space = basis->fe_space;
479   return CEED_ERROR_SUCCESS;
480 }
481 
482 /**
483   @brief Get dimension for given CeedElemTopology
484 
485   @param[in]  topo CeedElemTopology
486   @param[out] dim  Variable to store dimension of topology
487 
488   @return An error code: 0 - success, otherwise - failure
489 
490   @ref Backend
491 **/
492 int CeedBasisGetTopologyDimension(CeedElemTopology topo, CeedInt *dim) {
493   *dim = (CeedInt)topo >> 16;
494   return CEED_ERROR_SUCCESS;
495 }
496 
497 /**
498   @brief Get CeedTensorContract of a CeedBasis
499 
500   @param[in]  basis     CeedBasis
501   @param[out] contract  Variable to store CeedTensorContract
502 
503   @return An error code: 0 - success, otherwise - failure
504 
505   @ref Backend
506 **/
507 int CeedBasisGetTensorContract(CeedBasis basis, CeedTensorContract *contract) {
508   *contract = basis->contract;
509   return CEED_ERROR_SUCCESS;
510 }
511 
512 /**
513   @brief Set CeedTensorContract of a CeedBasis
514 
515   @param[in,out] basis    CeedBasis
516   @param[in]     contract CeedTensorContract to set
517 
518   @return An error code: 0 - success, otherwise - failure
519 
520   @ref Backend
521 **/
522 int CeedBasisSetTensorContract(CeedBasis basis, CeedTensorContract contract) {
523   basis->contract = contract;
524   CeedCall(CeedTensorContractReference(contract));
525   return CEED_ERROR_SUCCESS;
526 }
527 
528 /**
529   @brief Return a reference implementation of matrix multiplication C = A B.
530 
531   Note: This is a reference implementation for CPU CeedScalar pointers that is not intended for high performance.
532 
533   @param[in]  ceed  Ceed context for error handling
534   @param[in]  mat_A Row-major matrix A
535   @param[in]  mat_B Row-major matrix B
536   @param[out] mat_C Row-major output matrix C
537   @param[in]  m     Number of rows of C
538   @param[in]  n     Number of columns of C
539   @param[in]  kk    Number of columns of A/rows of B
540 
541   @return An error code: 0 - success, otherwise - failure
542 
543   @ref Utility
544 **/
545 int CeedMatrixMatrixMultiply(Ceed ceed, const CeedScalar *mat_A, const CeedScalar *mat_B, CeedScalar *mat_C, CeedInt m, CeedInt n, CeedInt kk) {
546   for (CeedInt i = 0; i < m; i++) {
547     for (CeedInt j = 0; j < n; j++) {
548       CeedScalar sum = 0;
549       for (CeedInt k = 0; k < kk; k++) sum += mat_A[k + i * kk] * mat_B[j + k * n];
550       mat_C[j + i * n] = sum;
551     }
552   }
553   return CEED_ERROR_SUCCESS;
554 }
555 
556 /**
557   @brief Return QR Factorization of a matrix
558 
559   @param[in]     ceed Ceed context for error handling
560   @param[in,out] mat  Row-major matrix to be factorized in place
561   @param[in,out] tau  Vector of length m of scaling factors
562   @param[in]     m    Number of rows
563   @param[in]     n    Number of columns
564 
565   @return An error code: 0 - success, otherwise - failure
566 
567   @ref Utility
568 **/
569 int CeedQRFactorization(Ceed ceed, CeedScalar *mat, CeedScalar *tau, CeedInt m, CeedInt n) {
570   CeedScalar v[m];
571 
572   // Check matrix shape
573   CeedCheck(n <= m, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute QR factorization with n > m");
574 
575   for (CeedInt i = 0; i < n; i++) {
576     if (i >= m - 1) {  // last row of matrix, no reflection needed
577       tau[i] = 0.;
578       break;
579     }
580     // Calculate Householder vector, magnitude
581     CeedScalar sigma = 0.0;
582     v[i]             = mat[i + n * i];
583     for (CeedInt j = i + 1; j < m; j++) {
584       v[j] = mat[i + n * j];
585       sigma += v[j] * v[j];
586     }
587     CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:m]
588     CeedScalar R_ii = -copysign(norm, v[i]);
589     v[i] -= R_ii;
590     // norm of v[i:m] after modification above and scaling below
591     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
592     //   tau = 2 / (norm*norm)
593     tau[i] = 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
594     for (CeedInt j = i + 1; j < m; j++) v[j] /= v[i];
595 
596     // Apply Householder reflector to lower right panel
597     CeedHouseholderReflect(&mat[i * n + i + 1], &v[i], tau[i], m - i, n - i - 1, n, 1);
598     // Save v
599     mat[i + n * i] = R_ii;
600     for (CeedInt j = i + 1; j < m; j++) mat[i + n * j] = v[j];
601   }
602   return CEED_ERROR_SUCCESS;
603 }
604 
605 /**
606   @brief Apply Householder Q matrix
607 
608   Compute mat_A = mat_Q mat_A, where mat_Q is mxm and mat_A is mxn.
609 
610   @param[in,out] mat_A  Matrix to apply Householder Q to, in place
611   @param[in]     mat_Q  Householder Q matrix
612   @param[in]     tau    Householder scaling factors
613   @param[in]     t_mode Transpose mode for application
614   @param[in]     m      Number of rows in A
615   @param[in]     n      Number of columns in A
616   @param[in]     k      Number of elementary reflectors in Q, k<m
617   @param[in]     row    Row stride in A
618   @param[in]     col    Col stride in A
619 
620   @return An error code: 0 - success, otherwise - failure
621 
622   @ref Utility
623 **/
624 int CeedHouseholderApplyQ(CeedScalar *mat_A, const CeedScalar *mat_Q, const CeedScalar *tau, CeedTransposeMode t_mode, CeedInt m, CeedInt n,
625                           CeedInt k, CeedInt row, CeedInt col) {
626   CeedScalar *v;
627   CeedCall(CeedMalloc(m, &v));
628   for (CeedInt ii = 0; ii < k; ii++) {
629     CeedInt i = t_mode == CEED_TRANSPOSE ? ii : k - 1 - ii;
630     for (CeedInt j = i + 1; j < m; j++) v[j] = mat_Q[j * k + i];
631     // Apply Householder reflector (I - tau v v^T) collo_grad_1d^T
632     CeedCall(CeedHouseholderReflect(&mat_A[i * row], &v[i], tau[i], m - i, n, row, col));
633   }
634   CeedCall(CeedFree(&v));
635   return CEED_ERROR_SUCCESS;
636 }
637 
638 /**
639   @brief Return symmetric Schur decomposition of the symmetric matrix mat via symmetric QR factorization
640 
641   @param[in]     ceed   Ceed context for error handling
642   @param[in,out] mat    Row-major matrix to be factorized in place
643   @param[out]    lambda Vector of length n of eigenvalues
644   @param[in]     n      Number of rows/columns
645 
646   @return An error code: 0 - success, otherwise - failure
647 
648   @ref Utility
649 **/
650 CeedPragmaOptimizeOff
651 int CeedSymmetricSchurDecomposition(Ceed ceed, CeedScalar *mat, CeedScalar *lambda, CeedInt n) {
652   // Check bounds for clang-tidy
653   CeedCheck(n > 1, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute symmetric Schur decomposition of scalars");
654 
655   CeedScalar v[n - 1], tau[n - 1], mat_T[n * n];
656 
657   // Copy mat to mat_T and set mat to I
658   memcpy(mat_T, mat, n * n * sizeof(mat[0]));
659   for (CeedInt i = 0; i < n; i++) {
660     for (CeedInt j = 0; j < n; j++) mat[j + n * i] = (i == j) ? 1 : 0;
661   }
662 
663   // Reduce to tridiagonal
664   for (CeedInt i = 0; i < n - 1; i++) {
665     // Calculate Householder vector, magnitude
666     CeedScalar sigma = 0.0;
667     v[i]             = mat_T[i + n * (i + 1)];
668     for (CeedInt j = i + 1; j < n - 1; j++) {
669       v[j] = mat_T[i + n * (j + 1)];
670       sigma += v[j] * v[j];
671     }
672     CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:n-1]
673     CeedScalar R_ii = -copysign(norm, v[i]);
674     v[i] -= R_ii;
675     // norm of v[i:m] after modification above and scaling below
676     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
677     //   tau = 2 / (norm*norm)
678     tau[i] = i == n - 2 ? 2 : 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
679     for (CeedInt j = i + 1; j < n - 1; j++) v[j] /= v[i];
680 
681     // Update sub and super diagonal
682     for (CeedInt j = i + 2; j < n; j++) {
683       mat_T[i + n * j] = 0;
684       mat_T[j + n * i] = 0;
685     }
686     // Apply symmetric Householder reflector to lower right panel
687     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
688     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), 1, n);
689 
690     // Save v
691     mat_T[i + n * (i + 1)] = R_ii;
692     mat_T[(i + 1) + n * i] = R_ii;
693     for (CeedInt j = i + 1; j < n - 1; j++) {
694       mat_T[i + n * (j + 1)] = v[j];
695     }
696   }
697   // Backwards accumulation of Q
698   for (CeedInt i = n - 2; i >= 0; i--) {
699     if (tau[i] > 0.0) {
700       v[i] = 1;
701       for (CeedInt j = i + 1; j < n - 1; j++) {
702         v[j]                   = mat_T[i + n * (j + 1)];
703         mat_T[i + n * (j + 1)] = 0;
704       }
705       CeedHouseholderReflect(&mat[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
706     }
707   }
708 
709   // Reduce sub and super diagonal
710   CeedInt    p = 0, q = 0, itr = 0, max_itr = n * n * n * n;
711   CeedScalar tol = CEED_EPSILON;
712 
713   while (itr < max_itr) {
714     // Update p, q, size of reduced portions of diagonal
715     p = 0;
716     q = 0;
717     for (CeedInt i = n - 2; i >= 0; i--) {
718       if (fabs(mat_T[i + n * (i + 1)]) < tol) q += 1;
719       else break;
720     }
721     for (CeedInt i = 0; i < n - q - 1; i++) {
722       if (fabs(mat_T[i + n * (i + 1)]) < tol) p += 1;
723       else break;
724     }
725     if (q == n - 1) break;  // Finished reducing
726 
727     // Reduce tridiagonal portion
728     CeedScalar t_nn = mat_T[(n - 1 - q) + n * (n - 1 - q)], t_nnm1 = mat_T[(n - 2 - q) + n * (n - 1 - q)];
729     CeedScalar d  = (mat_T[(n - 2 - q) + n * (n - 2 - q)] - t_nn) / 2;
730     CeedScalar mu = t_nn - t_nnm1 * t_nnm1 / (d + copysign(sqrt(d * d + t_nnm1 * t_nnm1), d));
731     CeedScalar x  = mat_T[p + n * p] - mu;
732     CeedScalar z  = mat_T[p + n * (p + 1)];
733     for (CeedInt k = p; k < n - q - 1; k++) {
734       // Compute Givens rotation
735       CeedScalar c = 1, s = 0;
736       if (fabs(z) > tol) {
737         if (fabs(z) > fabs(x)) {
738           CeedScalar tau = -x / z;
739           s = 1 / sqrt(1 + tau * tau), c = s * tau;
740         } else {
741           CeedScalar tau = -z / x;
742           c = 1 / sqrt(1 + tau * tau), s = c * tau;
743         }
744       }
745 
746       // Apply Givens rotation to T
747       CeedGivensRotation(mat_T, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
748       CeedGivensRotation(mat_T, c, s, CEED_TRANSPOSE, k, k + 1, n, n);
749 
750       // Apply Givens rotation to Q
751       CeedGivensRotation(mat, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
752 
753       // Update x, z
754       if (k < n - q - 2) {
755         x = mat_T[k + n * (k + 1)];
756         z = mat_T[k + n * (k + 2)];
757       }
758     }
759     itr++;
760   }
761 
762   // Save eigenvalues
763   for (CeedInt i = 0; i < n; i++) lambda[i] = mat_T[i + n * i];
764 
765   // Check convergence
766   CeedCheck(itr < max_itr || q > n, ceed, CEED_ERROR_MINOR, "Symmetric QR failed to converge");
767   return CEED_ERROR_SUCCESS;
768 }
769 CeedPragmaOptimizeOn
770 
771 /**
772   @brief Return Simultaneous Diagonalization of two matrices.
773 
774   This solves the generalized eigenvalue problem A x = lambda B x, where A and B are symmetric and B is positive definite.
775   We generate the matrix X and vector Lambda such that X^T A X = Lambda and X^T B X = I.
776   This is equivalent to the LAPACK routine 'sygv' with TYPE = 1.
777 
778   @param[in]  ceed   Ceed context for error handling
779   @param[in]  mat_A  Row-major matrix to be factorized with eigenvalues
780   @param[in]  mat_B  Row-major matrix to be factorized to identity
781   @param[out] mat_X  Row-major orthogonal matrix
782   @param[out] lambda Vector of length n of generalized eigenvalues
783   @param[in]  n      Number of rows/columns
784 
785   @return An error code: 0 - success, otherwise - failure
786 
787   @ref Utility
788 **/
789 CeedPragmaOptimizeOff
790 int CeedSimultaneousDiagonalization(Ceed ceed, CeedScalar *mat_A, CeedScalar *mat_B, CeedScalar *mat_X, CeedScalar *lambda, CeedInt n) {
791   CeedScalar *mat_C, *mat_G, *vec_D;
792   CeedCall(CeedCalloc(n * n, &mat_C));
793   CeedCall(CeedCalloc(n * n, &mat_G));
794   CeedCall(CeedCalloc(n, &vec_D));
795 
796   // Compute B = G D G^T
797   memcpy(mat_G, mat_B, n * n * sizeof(mat_B[0]));
798   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_G, vec_D, n));
799 
800   // Sort eigenvalues
801   for (CeedInt i = n - 1; i >= 0; i--) {
802     for (CeedInt j = 0; j < i; j++) {
803       if (fabs(vec_D[j]) > fabs(vec_D[j + 1])) {
804         CeedScalar temp;
805         temp         = vec_D[j];
806         vec_D[j]     = vec_D[j + 1];
807         vec_D[j + 1] = temp;
808         for (CeedInt k = 0; k < n; k++) {
809           temp                 = mat_G[k * n + j];
810           mat_G[k * n + j]     = mat_G[k * n + j + 1];
811           mat_G[k * n + j + 1] = temp;
812         }
813       }
814     }
815   }
816 
817   // Compute C = (G D^1/2)^-1 A (G D^1/2)^-T
818   //           = D^-1/2 G^T A G D^-1/2
819   // -- D = D^-1/2
820   for (CeedInt i = 0; i < n; i++) vec_D[i] = 1. / sqrt(vec_D[i]);
821   // -- G = G D^-1/2
822   // -- C = D^-1/2 G^T
823   for (CeedInt i = 0; i < n; i++) {
824     for (CeedInt j = 0; j < n; j++) {
825       mat_G[i * n + j] *= vec_D[j];
826       mat_C[j * n + i] = mat_G[i * n + j];
827     }
828   }
829   // -- X = (D^-1/2 G^T) A
830   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_C, (const CeedScalar *)mat_A, mat_X, n, n, n));
831   // -- C = (D^-1/2 G^T A) (G D^-1/2)
832   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_X, (const CeedScalar *)mat_G, mat_C, n, n, n));
833 
834   // Compute Q^T C Q = lambda
835   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_C, lambda, n));
836 
837   // Sort eigenvalues
838   for (CeedInt i = n - 1; i >= 0; i--) {
839     for (CeedInt j = 0; j < i; j++) {
840       if (fabs(lambda[j]) > fabs(lambda[j + 1])) {
841         CeedScalar temp;
842         temp          = lambda[j];
843         lambda[j]     = lambda[j + 1];
844         lambda[j + 1] = temp;
845         for (CeedInt k = 0; k < n; k++) {
846           temp                 = mat_C[k * n + j];
847           mat_C[k * n + j]     = mat_C[k * n + j + 1];
848           mat_C[k * n + j + 1] = temp;
849         }
850       }
851     }
852   }
853 
854   // Set X = (G D^1/2)^-T Q
855   //       = G D^-1/2 Q
856   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_G, (const CeedScalar *)mat_C, mat_X, n, n, n));
857 
858   // Cleanup
859   CeedCall(CeedFree(&mat_C));
860   CeedCall(CeedFree(&mat_G));
861   CeedCall(CeedFree(&vec_D));
862   return CEED_ERROR_SUCCESS;
863 }
864 CeedPragmaOptimizeOn
865 
866 /// @}
867 
868 /// ----------------------------------------------------------------------------
869 /// CeedBasis Public API
870 /// ----------------------------------------------------------------------------
871 /// @addtogroup CeedBasisUser
872 /// @{
873 
874 /**
875   @brief Create a tensor-product basis for H^1 discretizations
876 
877   @param[in]  ceed        Ceed object where the CeedBasis will be created
878   @param[in]  dim         Topological dimension
879   @param[in]  num_comp    Number of field components (1 for scalar fields)
880   @param[in]  P_1d        Number of nodes in one dimension
881   @param[in]  Q_1d        Number of quadrature points in one dimension
882   @param[in]  interp_1d   Row-major (Q_1d * P_1d) matrix expressing the values of nodal basis functions at quadrature points
883   @param[in]  grad_1d     Row-major (Q_1d * P_1d) matrix expressing derivatives of nodal basis functions at quadrature points
884   @param[in]  q_ref_1d    Array of length Q_1d holding the locations of quadrature points on the 1D reference element [-1, 1]
885   @param[in]  q_weight_1d Array of length Q_1d holding the quadrature weights on the reference element
886   @param[out] basis       Address of the variable where the newly created CeedBasis will be stored.
887 
888   @return An error code: 0 - success, otherwise - failure
889 
890   @ref User
891 **/
892 int CeedBasisCreateTensorH1(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P_1d, CeedInt Q_1d, const CeedScalar *interp_1d,
893                             const CeedScalar *grad_1d, const CeedScalar *q_ref_1d, const CeedScalar *q_weight_1d, CeedBasis *basis) {
894   if (!ceed->BasisCreateTensorH1) {
895     Ceed delegate;
896 
897     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
898     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not support BasisCreateTensorH1");
899     CeedCall(CeedBasisCreateTensorH1(delegate, dim, num_comp, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
900     return CEED_ERROR_SUCCESS;
901   }
902 
903   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "Basis dimension must be a positive value");
904   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 component");
905   CeedCheck(P_1d > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 node");
906   CeedCheck(Q_1d > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 quadrature point");
907 
908   CeedElemTopology topo = dim == 1 ? CEED_TOPOLOGY_LINE : dim == 2 ? CEED_TOPOLOGY_QUAD : CEED_TOPOLOGY_HEX;
909 
910   CeedCall(CeedCalloc(1, basis));
911   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
912   (*basis)->ref_count       = 1;
913   (*basis)->is_tensor_basis = true;
914   (*basis)->dim             = dim;
915   (*basis)->topo            = topo;
916   (*basis)->num_comp        = num_comp;
917   (*basis)->P_1d            = P_1d;
918   (*basis)->Q_1d            = Q_1d;
919   (*basis)->P               = CeedIntPow(P_1d, dim);
920   (*basis)->Q               = CeedIntPow(Q_1d, dim);
921   (*basis)->fe_space        = CEED_FE_SPACE_H1;
922   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_ref_1d));
923   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_weight_1d));
924   if (q_ref_1d) memcpy((*basis)->q_ref_1d, q_ref_1d, Q_1d * sizeof(q_ref_1d[0]));
925   if (q_weight_1d) memcpy((*basis)->q_weight_1d, q_weight_1d, Q_1d * sizeof(q_weight_1d[0]));
926   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->interp_1d));
927   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->grad_1d));
928   if (interp_1d) memcpy((*basis)->interp_1d, interp_1d, Q_1d * P_1d * sizeof(interp_1d[0]));
929   if (grad_1d) memcpy((*basis)->grad_1d, grad_1d, Q_1d * P_1d * sizeof(grad_1d[0]));
930   CeedCall(ceed->BasisCreateTensorH1(dim, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, *basis));
931   return CEED_ERROR_SUCCESS;
932 }
933 
934 /**
935   @brief Create a tensor-product Lagrange basis
936 
937   @param[in]  ceed      Ceed object where the CeedBasis will be created
938   @param[in]  dim       Topological dimension of element
939   @param[in]  num_comp  Number of field components (1 for scalar fields)
940   @param[in]  P         Number of Gauss-Lobatto nodes in one dimension.
941                           The polynomial degree of the resulting Q_k element is k=P-1.
942   @param[in]  Q         Number of quadrature points in one dimension.
943   @param[in]  quad_mode Distribution of the Q quadrature points (affects order of accuracy for the quadrature)
944   @param[out] basis     Address of the variable where the newly created CeedBasis will be stored.
945 
946   @return An error code: 0 - success, otherwise - failure
947 
948   @ref User
949 **/
950 int CeedBasisCreateTensorH1Lagrange(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P, CeedInt Q, CeedQuadMode quad_mode, CeedBasis *basis) {
951   // Allocate
952   int        ierr = CEED_ERROR_SUCCESS;
953   CeedScalar c1, c2, c3, c4, dx, *nodes, *interp_1d, *grad_1d, *q_ref_1d, *q_weight_1d;
954 
955   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "Basis dimension must be a positive value");
956   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 component");
957   CeedCheck(P > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 node");
958   CeedCheck(Q > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 quadrature point");
959 
960   // Get Nodes and Weights
961   CeedCall(CeedCalloc(P * Q, &interp_1d));
962   CeedCall(CeedCalloc(P * Q, &grad_1d));
963   CeedCall(CeedCalloc(P, &nodes));
964   CeedCall(CeedCalloc(Q, &q_ref_1d));
965   CeedCall(CeedCalloc(Q, &q_weight_1d));
966   if (CeedLobattoQuadrature(P, nodes, NULL) != CEED_ERROR_SUCCESS) goto cleanup;
967   switch (quad_mode) {
968     case CEED_GAUSS:
969       ierr = CeedGaussQuadrature(Q, q_ref_1d, q_weight_1d);
970       break;
971     case CEED_GAUSS_LOBATTO:
972       ierr = CeedLobattoQuadrature(Q, q_ref_1d, q_weight_1d);
973       break;
974   }
975   if (ierr != CEED_ERROR_SUCCESS) goto cleanup;
976 
977   // Build B, D matrix
978   // Fornberg, 1998
979   for (CeedInt i = 0; i < Q; i++) {
980     c1                   = 1.0;
981     c3                   = nodes[0] - q_ref_1d[i];
982     interp_1d[i * P + 0] = 1.0;
983     for (CeedInt j = 1; j < P; j++) {
984       c2 = 1.0;
985       c4 = c3;
986       c3 = nodes[j] - q_ref_1d[i];
987       for (CeedInt k = 0; k < j; k++) {
988         dx = nodes[j] - nodes[k];
989         c2 *= dx;
990         if (k == j - 1) {
991           grad_1d[i * P + j]   = c1 * (interp_1d[i * P + k] - c4 * grad_1d[i * P + k]) / c2;
992           interp_1d[i * P + j] = -c1 * c4 * interp_1d[i * P + k] / c2;
993         }
994         grad_1d[i * P + k]   = (c3 * grad_1d[i * P + k] - interp_1d[i * P + k]) / dx;
995         interp_1d[i * P + k] = c3 * interp_1d[i * P + k] / dx;
996       }
997       c1 = c2;
998     }
999   }
1000   // Pass to CeedBasisCreateTensorH1
1001   CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P, Q, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1002 cleanup:
1003   CeedCall(CeedFree(&interp_1d));
1004   CeedCall(CeedFree(&grad_1d));
1005   CeedCall(CeedFree(&nodes));
1006   CeedCall(CeedFree(&q_ref_1d));
1007   CeedCall(CeedFree(&q_weight_1d));
1008   return CEED_ERROR_SUCCESS;
1009 }
1010 
1011 /**
1012   @brief Create a non tensor-product basis for H^1 discretizations
1013 
1014   @param[in]  ceed      Ceed object where the CeedBasis will be created
1015   @param[in]  topo      Topology of element, e.g. hypercube, simplex, ect
1016   @param[in]  num_comp  Number of field components (1 for scalar fields)
1017   @param[in]  num_nodes Total number of nodes
1018   @param[in]  num_qpts  Total number of quadrature points
1019   @param[in]  interp    Row-major (num_qpts * num_nodes) matrix expressing the values of nodal basis functions at quadrature points
1020   @param[in]  grad      Row-major (dim * num_qpts * num_nodes) matrix expressing derivatives of nodal basis functions at quadrature points
1021   @param[in]  q_ref     Array of length num_qpts * dim holding the locations of quadrature points on the reference element
1022   @param[in]  q_weight  Array of length num_qpts holding the quadrature weights on the reference element
1023   @param[out] basis     Address of the variable where the newly created CeedBasis will be stored.
1024 
1025   @return An error code: 0 - success, otherwise - failure
1026 
1027   @ref User
1028 **/
1029 int CeedBasisCreateH1(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1030                       const CeedScalar *grad, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1031   CeedInt P = num_nodes, Q = num_qpts, dim = 0;
1032 
1033   if (!ceed->BasisCreateH1) {
1034     Ceed delegate;
1035 
1036     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1037     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not support BasisCreateH1");
1038     CeedCall(CeedBasisCreateH1(delegate, topo, num_comp, num_nodes, num_qpts, interp, grad, q_ref, q_weight, basis));
1039     return CEED_ERROR_SUCCESS;
1040   }
1041 
1042   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 component");
1043   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 node");
1044   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 quadrature point");
1045 
1046   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1047 
1048   CeedCall(CeedCalloc(1, basis));
1049   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1050   (*basis)->ref_count       = 1;
1051   (*basis)->is_tensor_basis = false;
1052   (*basis)->dim             = dim;
1053   (*basis)->topo            = topo;
1054   (*basis)->num_comp        = num_comp;
1055   (*basis)->P               = P;
1056   (*basis)->Q               = Q;
1057   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1058   CeedCall(CeedCalloc(Q * dim, &(*basis)->q_ref_1d));
1059   CeedCall(CeedCalloc(Q, &(*basis)->q_weight_1d));
1060   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1061   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1062   CeedCall(CeedCalloc(Q * P, &(*basis)->interp));
1063   CeedCall(CeedCalloc(dim * Q * P, &(*basis)->grad));
1064   if (interp) memcpy((*basis)->interp, interp, Q * P * sizeof(interp[0]));
1065   if (grad) memcpy((*basis)->grad, grad, dim * Q * P * sizeof(grad[0]));
1066   CeedCall(ceed->BasisCreateH1(topo, dim, P, Q, interp, grad, q_ref, q_weight, *basis));
1067   return CEED_ERROR_SUCCESS;
1068 }
1069 
1070 /**
1071   @brief Create a non tensor-product basis for \f$H(\mathrm{div})\f$ discretizations
1072 
1073   @param[in]  ceed      Ceed object where the CeedBasis will be created
1074   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1075   @param[in]  num_comp  Number of components (usually 1 for vectors in H(div) bases)
1076   @param[in]  num_nodes Total number of nodes (dofs per element)
1077   @param[in]  num_qpts  Total number of quadrature points
1078   @param[in]  interp    Row-major (dim * num_qpts * num_nodes) matrix expressing the values of basis functions at quadrature points
1079   @param[in]  div       Row-major (num_qpts * num_nodes) matrix expressing divergence of basis functions at quadrature points
1080   @param[in]  q_ref     Array of length num_qpts * dim holding the locations of quadrature points on the reference element
1081   @param[in]  q_weight  Array of length num_qpts holding the quadrature weights on the reference element
1082   @param[out] basis     Address of the variable where the newly created CeedBasis will be stored.
1083 
1084   @return An error code: 0 - success, otherwise - failure
1085 
1086   @ref User
1087 **/
1088 int CeedBasisCreateHdiv(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1089                         const CeedScalar *div, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1090   CeedInt Q = num_qpts, P = num_nodes, dim = 0;
1091 
1092   if (!ceed->BasisCreateHdiv) {
1093     Ceed delegate;
1094 
1095     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1096     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHdiv");
1097     CeedCall(CeedBasisCreateHdiv(delegate, topo, num_comp, num_nodes, num_qpts, interp, div, q_ref, q_weight, basis));
1098     return CEED_ERROR_SUCCESS;
1099   }
1100 
1101   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 component");
1102   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 node");
1103   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 quadrature point");
1104 
1105   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1106 
1107   CeedCall(CeedCalloc(1, basis));
1108   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1109   (*basis)->ref_count       = 1;
1110   (*basis)->is_tensor_basis = false;
1111   (*basis)->dim             = dim;
1112   (*basis)->topo            = topo;
1113   (*basis)->num_comp        = num_comp;
1114   (*basis)->P               = P;
1115   (*basis)->Q               = Q;
1116   (*basis)->fe_space        = CEED_FE_SPACE_HDIV;
1117   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1118   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1119   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1120   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1121   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1122   CeedCall(CeedMalloc(Q * P, &(*basis)->div));
1123   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1124   if (div) memcpy((*basis)->div, div, Q * P * sizeof(div[0]));
1125   CeedCall(ceed->BasisCreateHdiv(topo, dim, P, Q, interp, div, q_ref, q_weight, *basis));
1126   return CEED_ERROR_SUCCESS;
1127 }
1128 
1129 /**
1130   @brief Create a non tensor-product basis for \f$H(\mathrm{curl})\f$ discretizations
1131 
1132   @param[in]  ceed      Ceed object where the CeedBasis will be created
1133   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1134   @param[in]  num_comp  Number of components (usually 1 for vectors in H(curl) bases)
1135   @param[in]  num_nodes Total number of nodes (dofs per element)
1136   @param[in]  num_qpts  Total number of quadrature points
1137   @param[in]  interp    Row-major (dim * num_qpts * num_nodes) matrix expressing the values of basis functions at quadrature points
1138   @param[in]  curl      Row-major (curl_comp * num_qpts * num_nodes, curl_comp = 1 if dim < 3 else dim) matrix expressing curl of basis functions at
1139 quadrature points
1140   @param[in]  q_ref     Array of length num_qpts * dim holding the locations of quadrature points on the reference element
1141   @param[in]  q_weight  Array of length num_qpts holding the quadrature weights on the reference element
1142   @param[out] basis     Address of the variable where the newly created CeedBasis will be stored.
1143 
1144   @return An error code: 0 - success, otherwise - failure
1145 
1146   @ref User
1147 **/
1148 int CeedBasisCreateHcurl(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1149                          const CeedScalar *curl, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1150   CeedInt Q = num_qpts, P = num_nodes, dim = 0, curl_comp = 0;
1151 
1152   if (!ceed->BasisCreateHdiv) {
1153     Ceed delegate;
1154 
1155     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1156     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHcurl");
1157     CeedCall(CeedBasisCreateHcurl(delegate, topo, num_comp, num_nodes, num_qpts, interp, curl, q_ref, q_weight, basis));
1158     return CEED_ERROR_SUCCESS;
1159   }
1160 
1161   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 component");
1162   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 node");
1163   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "Basis must have at least 1 quadrature point");
1164 
1165   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1166   curl_comp = (dim < 3) ? 1 : dim;
1167 
1168   CeedCall(CeedCalloc(1, basis));
1169   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1170   (*basis)->ref_count       = 1;
1171   (*basis)->is_tensor_basis = false;
1172   (*basis)->dim             = dim;
1173   (*basis)->topo            = topo;
1174   (*basis)->num_comp        = num_comp;
1175   (*basis)->P               = P;
1176   (*basis)->Q               = Q;
1177   (*basis)->fe_space        = CEED_FE_SPACE_HCURL;
1178   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1179   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1180   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1181   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1182   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1183   CeedCall(CeedMalloc(curl_comp * Q * P, &(*basis)->curl));
1184   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1185   if (curl) memcpy((*basis)->curl, curl, curl_comp * Q * P * sizeof(curl[0]));
1186   CeedCall(ceed->BasisCreateHcurl(topo, dim, P, Q, interp, curl, q_ref, q_weight, *basis));
1187   return CEED_ERROR_SUCCESS;
1188 }
1189 
1190 /**
1191   @brief Create a CeedBasis for projection from the nodes of `basis_from` to the nodes of `basis_to`.
1192 
1193   Only `CEED_EVAL_INTERP` will be valid for the new basis, `basis_project`.
1194   For H^1 spaces, `CEED_EVAL_GRAD` will also be valid.
1195   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR
1196 factorization.
1197   The gradient (for the H^1 case) is given by `grad_project = interp_to^+ * grad_from`.
1198 
1199   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
1200 
1201   Note: `basis_project` will have the same number of components as `basis_from`, regardless of the number of components that `basis_to` has.
1202         If `basis_from` has 3 components and `basis_to` has 5 components, then `basis_project` will have 3 components.
1203 
1204   @param[in]  basis_from    CeedBasis to prolong from
1205   @param[in]  basis_to      CeedBasis to prolong to
1206   @param[out] basis_project Address of the variable where the newly created CeedBasis will be stored.
1207 
1208   @return An error code: 0 - success, otherwise - failure
1209 
1210   @ref User
1211 **/
1212 int CeedBasisCreateProjection(CeedBasis basis_from, CeedBasis basis_to, CeedBasis *basis_project) {
1213   Ceed ceed;
1214   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
1215 
1216   // Create projection matrix
1217   CeedScalar *interp_project, *grad_project;
1218   CeedCall(CeedBasisCreateProjectionMatrices(basis_from, basis_to, &interp_project, &grad_project));
1219 
1220   // Build basis
1221   bool        is_tensor;
1222   CeedInt     dim, num_comp;
1223   CeedScalar *q_ref, *q_weight;
1224   CeedCall(CeedBasisIsTensor(basis_to, &is_tensor));
1225   CeedCall(CeedBasisGetDimension(basis_to, &dim));
1226   CeedCall(CeedBasisGetNumComponents(basis_from, &num_comp));
1227   if (is_tensor) {
1228     CeedInt P_1d_to, P_1d_from;
1229     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_1d_from));
1230     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_1d_to));
1231     CeedCall(CeedCalloc(P_1d_to, &q_ref));
1232     CeedCall(CeedCalloc(P_1d_to, &q_weight));
1233     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d_from, P_1d_to, interp_project, grad_project, q_ref, q_weight, basis_project));
1234   } else {
1235     // Even if basis_to and basis_from are not H1, the resulting basis is H1 for interpolation to work
1236     CeedElemTopology topo;
1237     CeedCall(CeedBasisGetTopology(basis_to, &topo));
1238     CeedInt num_nodes_to, num_nodes_from;
1239     CeedCall(CeedBasisGetNumNodes(basis_from, &num_nodes_from));
1240     CeedCall(CeedBasisGetNumNodes(basis_to, &num_nodes_to));
1241     CeedCall(CeedCalloc(num_nodes_to * dim, &q_ref));
1242     CeedCall(CeedCalloc(num_nodes_to, &q_weight));
1243     CeedCall(CeedBasisCreateH1(ceed, topo, num_comp, num_nodes_from, num_nodes_to, interp_project, grad_project, q_ref, q_weight, basis_project));
1244   }
1245 
1246   // Cleanup
1247   CeedCall(CeedFree(&interp_project));
1248   CeedCall(CeedFree(&grad_project));
1249   CeedCall(CeedFree(&q_ref));
1250   CeedCall(CeedFree(&q_weight));
1251 
1252   return CEED_ERROR_SUCCESS;
1253 }
1254 
1255 /**
1256   @brief Copy the pointer to a CeedBasis.
1257 
1258   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.
1259         This CeedBasis will be destroyed if `basis_copy` is the only reference to this CeedBasis.
1260 
1261   @param[in]     basis      CeedBasis to copy reference to
1262   @param[in,out] basis_copy Variable to store copied reference
1263 
1264   @return An error code: 0 - success, otherwise - failure
1265 
1266   @ref User
1267 **/
1268 int CeedBasisReferenceCopy(CeedBasis basis, CeedBasis *basis_copy) {
1269   if (basis != CEED_BASIS_COLLOCATED) CeedCall(CeedBasisReference(basis));
1270   CeedCall(CeedBasisDestroy(basis_copy));
1271   *basis_copy = basis;
1272   return CEED_ERROR_SUCCESS;
1273 }
1274 
1275 /**
1276   @brief View a CeedBasis
1277 
1278   @param[in] basis  CeedBasis to view
1279   @param[in] stream Stream to view to, e.g., stdout
1280 
1281   @return An error code: 0 - success, otherwise - failure
1282 
1283   @ref User
1284 **/
1285 int CeedBasisView(CeedBasis basis, FILE *stream) {
1286   CeedElemTopology topo     = basis->topo;
1287   CeedFESpace      fe_space = basis->fe_space;
1288   CeedInt          q_comp   = 0;
1289 
1290   // Print FE space and element topology of the basis
1291   if (basis->is_tensor_basis) {
1292     fprintf(stream, "CeedBasis (%s on a %s element): dim=%" CeedInt_FMT " P=%" CeedInt_FMT " Q=%" CeedInt_FMT "\n", CeedFESpaces[fe_space],
1293             CeedElemTopologies[topo], basis->dim, basis->P_1d, basis->Q_1d);
1294   } else {
1295     fprintf(stream, "CeedBasis (%s on a %s element): dim=%" CeedInt_FMT " P=%" CeedInt_FMT " Q=%" CeedInt_FMT "\n", CeedFESpaces[fe_space],
1296             CeedElemTopologies[topo], basis->dim, basis->P, basis->Q);
1297   }
1298   // Print quadrature data, interpolation/gradient/divergence/curl of the basis
1299   if (basis->is_tensor_basis) {  // tensor basis
1300     CeedCall(CeedScalarView("qref1d", "\t% 12.8f", 1, basis->Q_1d, basis->q_ref_1d, stream));
1301     CeedCall(CeedScalarView("qweight1d", "\t% 12.8f", 1, basis->Q_1d, basis->q_weight_1d, stream));
1302     CeedCall(CeedScalarView("interp1d", "\t% 12.8f", basis->Q_1d, basis->P_1d, basis->interp_1d, stream));
1303     CeedCall(CeedScalarView("grad1d", "\t% 12.8f", basis->Q_1d, basis->P_1d, basis->grad_1d, stream));
1304   } else {  // non-tensor basis
1305     CeedCall(CeedScalarView("qref", "\t% 12.8f", 1, basis->Q * basis->dim, basis->q_ref_1d, stream));
1306     CeedCall(CeedScalarView("qweight", "\t% 12.8f", 1, basis->Q, basis->q_weight_1d, stream));
1307     CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_INTERP, &q_comp));
1308     CeedCall(CeedScalarView("interp", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->interp, stream));
1309     if (basis->grad) {
1310       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_GRAD, &q_comp));
1311       CeedCall(CeedScalarView("grad", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->grad, stream));
1312     }
1313     if (basis->div) {
1314       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_DIV, &q_comp));
1315       CeedCall(CeedScalarView("div", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->div, stream));
1316     }
1317     if (basis->curl) {
1318       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_CURL, &q_comp));
1319       CeedCall(CeedScalarView("curl", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->curl, stream));
1320     }
1321   }
1322   return CEED_ERROR_SUCCESS;
1323 }
1324 
1325 /**
1326   @brief Apply basis evaluation from nodes to quadrature points or vice versa
1327 
1328   @param[in]  basis      CeedBasis to evaluate
1329   @param[in]  num_elem   The number of elements to apply the basis evaluation to;
1330                            the backend will specify the ordering in CeedElemRestrictionCreateBlocked()
1331   @param[in]  t_mode    \ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1332                           \ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1333   @param[in]  eval_mode \ref CEED_EVAL_NONE to use values directly,
1334                           \ref CEED_EVAL_INTERP to use interpolated values,
1335                           \ref CEED_EVAL_GRAD to use gradients,
1336                           \ref CEED_EVAL_DIV to use divergence,
1337                           \ref CEED_EVAL_CURL to use curl,
1338                           \ref CEED_EVAL_WEIGHT to use quadrature weights.
1339   @param[in]  u        Input CeedVector
1340   @param[out] v        Output CeedVector
1341 
1342   @return An error code: 0 - success, otherwise - failure
1343 
1344   @ref User
1345 **/
1346 int CeedBasisApply(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1347   CeedSize u_length = 0, v_length;
1348   CeedInt  dim, num_comp, q_comp, num_nodes, num_qpts;
1349   CeedCall(CeedBasisGetDimension(basis, &dim));
1350   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1351   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
1352   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1353   CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
1354   CeedCall(CeedVectorGetLength(v, &v_length));
1355   if (u) CeedCall(CeedVectorGetLength(u, &u_length));
1356 
1357   CeedCheck(basis->Apply, basis->ceed, CEED_ERROR_UNSUPPORTED, "Backend does not support BasisApply");
1358 
1359   // Check compatibility of topological and geometrical dimensions
1360   CeedCheck((t_mode == CEED_TRANSPOSE && v_length % num_nodes == 0 && u_length % num_qpts == 0) ||
1361                 (t_mode == CEED_NOTRANSPOSE && u_length % num_nodes == 0 && v_length % num_qpts == 0),
1362             basis->ceed, CEED_ERROR_DIMENSION, "Length of input/output vectors incompatible with basis dimensions");
1363 
1364   // Check vector lengths to prevent out of bounds issues
1365   bool good_dims = true;
1366   switch (eval_mode) {
1367     case CEED_EVAL_NONE:
1368     case CEED_EVAL_INTERP:
1369     case CEED_EVAL_GRAD:
1370     case CEED_EVAL_DIV:
1371     case CEED_EVAL_CURL:
1372       good_dims =
1373           ((t_mode == CEED_TRANSPOSE && u_length >= num_elem * num_comp * num_qpts * q_comp && v_length >= num_elem * num_comp * num_nodes) ||
1374            (t_mode == CEED_NOTRANSPOSE && v_length >= num_elem * num_qpts * num_comp * q_comp && u_length >= num_elem * num_comp * num_nodes));
1375       break;
1376     case CEED_EVAL_WEIGHT:
1377       good_dims = v_length >= num_elem * num_qpts;
1378       break;
1379   }
1380   CeedCheck(good_dims, basis->ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
1381 
1382   CeedCall(basis->Apply(basis, num_elem, t_mode, eval_mode, u, v));
1383   return CEED_ERROR_SUCCESS;
1384 }
1385 
1386 /**
1387   @brief Apply basis evaluation from nodes to arbitrary points
1388 
1389   @param[in]  basis      CeedBasis to evaluate
1390   @param[in]  num_points The number of points to apply the basis evaluation to
1391   @param[in]  t_mode    \ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1392                           \ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
1393   @param[in]  eval_mode \ref CEED_EVAL_INTERP to use interpolated values,
1394                           \ref CEED_EVAL_GRAD to use gradients
1395   @param[in]  x_ref    CeedVector holding reference coordinates of each point
1396   @param[in]  u        Input CeedVector, of length `num_nodes * num_comp` for `CEED_NOTRANSPOSE`
1397   @param[out] v        Output CeedVector, of length `num_points * num_q_comp` for `CEED_NOTRANSPOSE` with `CEED_EVAL_INTERP`
1398 
1399   @return An error code: 0 - success, otherwise - failure
1400 
1401   @ref User
1402 **/
1403 int CeedBasisApplyAtPoints(CeedBasis basis, CeedInt num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u,
1404                            CeedVector v) {
1405   CeedSize x_length = 0, u_length = 0, v_length;
1406   CeedInt  dim, num_comp, num_q_comp, num_nodes, P_1d = 1, Q_1d = 1;
1407 
1408   CeedCall(CeedBasisGetDimension(basis, &dim));
1409   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
1410   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
1411   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1412   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &num_q_comp));
1413   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1414   CeedCall(CeedVectorGetLength(x_ref, &x_length));
1415   CeedCall(CeedVectorGetLength(v, &v_length));
1416   CeedCall(CeedVectorGetLength(u, &u_length));
1417 
1418   // Check compatibility of topological and geometrical dimensions
1419   CeedCheck((t_mode == CEED_TRANSPOSE && v_length % num_nodes == 0) || (t_mode == CEED_NOTRANSPOSE && u_length % num_nodes == 0), basis->ceed,
1420             CEED_ERROR_DIMENSION, "Length of input/output vectors incompatible with basis dimensions and number of points");
1421 
1422   // Check compatibility coordinates vector
1423   CeedCheck(x_length >= num_points * dim, basis->ceed, CEED_ERROR_DIMENSION,
1424             "Length of reference coordinate vector incompatible with basis dimension and number of points");
1425 
1426   // Check vector lengths to prevent out of bounds issues
1427   bool good_dims = false;
1428   switch (eval_mode) {
1429     case CEED_EVAL_INTERP:
1430       good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= num_points * num_q_comp || v_length >= num_nodes * num_comp)) ||
1431                    (t_mode == CEED_NOTRANSPOSE && (v_length >= num_points * num_q_comp || u_length >= num_nodes * num_comp)));
1432       break;
1433     case CEED_EVAL_GRAD:
1434       good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= num_points * num_q_comp * dim || v_length >= num_nodes * num_comp)) ||
1435                    (t_mode == CEED_NOTRANSPOSE && (v_length >= num_points * num_q_comp * dim || u_length >= num_nodes * num_comp)));
1436       break;
1437     case CEED_EVAL_NONE:
1438     case CEED_EVAL_WEIGHT:
1439     case CEED_EVAL_DIV:
1440     case CEED_EVAL_CURL:
1441       // LCOV_EXCL_START
1442       return CeedError(basis->ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points not supported for %s", CeedEvalModes[eval_mode]);
1443       // LCOV_EXCL_STOP
1444   }
1445   CeedCheck(good_dims, basis->ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
1446 
1447   // Backend method
1448   if (basis->ApplyAtPoints) {
1449     CeedCall(basis->ApplyAtPoints(basis, num_points, t_mode, eval_mode, x_ref, u, v));
1450     return CEED_ERROR_SUCCESS;
1451   }
1452 
1453   // Default implementation
1454   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points only supported for tensor product bases");
1455   CeedCheck(eval_mode == CEED_EVAL_INTERP || t_mode == CEED_NOTRANSPOSE, basis->ceed, CEED_ERROR_UNSUPPORTED, "%s evaluation only supported for %s",
1456             CeedEvalModes[eval_mode], CeedTransposeModes[CEED_NOTRANSPOSE]);
1457   if (!basis->basis_chebyshev) {
1458     // Build matrix mapping from quadrature point values to Chebyshev coefficients
1459     CeedScalar       *tau, *C, *I, *chebyshev_coeffs_1d;
1460     const CeedScalar *q_ref_1d;
1461 
1462     // Build coefficient matrix
1463     // -- Note: Clang-tidy needs this check because it does not understand the is_tensor_basis check above
1464     CeedCheck(P_1d > 0 && Q_1d > 0, basis->ceed, CEED_ERROR_INCOMPATIBLE, "Basis dimensions are malformed");
1465     CeedCall(CeedCalloc(Q_1d * Q_1d, &C));
1466     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
1467     for (CeedInt i = 0; i < Q_1d; i++) {
1468       const CeedScalar x = q_ref_1d[i];
1469 
1470       C[i * Q_1d + 0] = 1.0;
1471       C[i * Q_1d + 1] = 2 * x;
1472       for (CeedInt j = 2; j < Q_1d; j++) C[i * Q_1d + j] = 2 * x * C[i * Q_1d + j - 1] - C[i * Q_1d + j - 2];
1473     }
1474 
1475     // Inverse of coefficient matrix
1476     CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_coeffs_1d));
1477     CeedCall(CeedCalloc(Q_1d * Q_1d, &I));
1478     CeedCall(CeedCalloc(Q_1d, &tau));
1479     // -- QR Factorization, C = Q R
1480     CeedCall(CeedQRFactorization(basis->ceed, C, tau, Q_1d, Q_1d));
1481     // -- chebyshev_coeffs_1d = R_inv Q^T
1482     for (CeedInt i = 0; i < Q_1d; i++) I[i * Q_1d + i] = 1.0;
1483     // ---- Apply R_inv, chebyshev_coeffs_1d = I R_inv
1484     for (CeedInt i = 0; i < Q_1d; i++) {  // Row i
1485       chebyshev_coeffs_1d[Q_1d * i] = I[Q_1d * i] / C[0];
1486       for (CeedInt j = 1; j < Q_1d; j++) {  // Column j
1487         chebyshev_coeffs_1d[j + Q_1d * i] = I[j + Q_1d * i];
1488         for (CeedInt k = 0; k < j; k++) chebyshev_coeffs_1d[j + Q_1d * i] -= C[j + Q_1d * k] * chebyshev_coeffs_1d[k + Q_1d * i];
1489         chebyshev_coeffs_1d[j + Q_1d * i] /= C[j + Q_1d * j];
1490       }
1491     }
1492     // ---- Apply Q^T, chebyshev_coeffs_1d = R_inv Q^T
1493     CeedCall(CeedHouseholderApplyQ(chebyshev_coeffs_1d, C, tau, CEED_NOTRANSPOSE, Q_1d, Q_1d, Q_1d, 1, Q_1d));
1494 
1495     // Build basis mapping from nodes to Chebyshev coefficients
1496     CeedScalar       *chebyshev_interp_1d, *chebyshev_grad_1d, *chebyshev_q_weight_1d;
1497     const CeedScalar *interp_1d;
1498 
1499     CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_interp_1d));
1500     CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_grad_1d));
1501     CeedCall(CeedCalloc(Q_1d, &chebyshev_q_weight_1d));
1502     CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
1503     CeedCall(CeedMatrixMatrixMultiply(basis->ceed, chebyshev_coeffs_1d, interp_1d, chebyshev_interp_1d, Q_1d, P_1d, Q_1d));
1504 
1505     CeedCall(CeedVectorCreate(basis->ceed, num_comp * CeedIntPow(Q_1d, dim), &basis->vec_chebyshev));
1506     CeedCall(CeedBasisCreateTensorH1(basis->ceed, dim, num_comp, Q_1d, Q_1d, chebyshev_interp_1d, chebyshev_grad_1d, q_ref_1d, chebyshev_q_weight_1d,
1507                                      &basis->basis_chebyshev));
1508 
1509     // Cleanup
1510     CeedCall(CeedFree(&C));
1511     CeedCall(CeedFree(&chebyshev_coeffs_1d));
1512     CeedCall(CeedFree(&I));
1513     CeedCall(CeedFree(&tau));
1514     CeedCall(CeedFree(&chebyshev_interp_1d));
1515     CeedCall(CeedFree(&chebyshev_grad_1d));
1516     CeedCall(CeedFree(&chebyshev_q_weight_1d));
1517   }
1518 
1519   // Create TensorContract object if needed, such as a basis from the GPU backends
1520   if (!basis->contract) {
1521     Ceed      ceed_ref;
1522     CeedBasis basis_ref;
1523 
1524     CeedCall(CeedInit("/cpu/self", &ceed_ref));
1525     // Only need matching tensor contraction dimensions, any type of basis will work
1526     CeedCall(CeedBasisCreateTensorH1Lagrange(ceed_ref, dim, num_comp, Q_1d, Q_1d, CEED_GAUSS, &basis_ref));
1527     CeedCall(CeedTensorContractReference(basis_ref->contract));
1528     basis->contract = basis_ref->contract;
1529     CeedCall(CeedBasisDestroy(&basis_ref));
1530     CeedCall(CeedDestroy(&ceed_ref));
1531   }
1532 
1533   // Basis evaluation
1534   switch (t_mode) {
1535     case CEED_NOTRANSPOSE: {
1536       // Nodes to arbitrary points
1537       CeedScalar       *v_array;
1538       const CeedScalar *chebyshev_coeffs, *x_array_read;
1539 
1540       // -- Interpolate to Chebyshev coefficients
1541       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_NOTRANSPOSE, CEED_EVAL_INTERP, u, basis->vec_chebyshev));
1542 
1543       // -- Evaluate Chebyshev polynomials at arbitrary points
1544       CeedCall(CeedVectorGetArrayRead(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
1545       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
1546       CeedCall(CeedVectorGetArrayWrite(v, CEED_MEM_HOST, &v_array));
1547       switch (eval_mode) {
1548         case CEED_EVAL_INTERP: {
1549           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
1550 
1551           // ---- Values at point
1552           for (CeedInt p = 0; p < num_points; p++) {
1553             CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
1554 
1555             for (CeedInt d = dim - 1; d >= 0; d--) {
1556               // ------ Compute Chebyshev polynomial values
1557               {
1558                 const CeedScalar x = x_array_read[p * dim + d];
1559 
1560                 chebyshev_x[0] = 1.0;
1561                 chebyshev_x[1] = 2 * x;
1562                 for (CeedInt j = 2; j < Q_1d; j++) chebyshev_x[j] = 2 * x * chebyshev_x[j - 1] - chebyshev_x[j - 2];
1563               }
1564               // ------ Tensor contract
1565               CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
1566                                                d == (dim - 1) ? chebyshev_coeffs : tmp[d % 2], d == 0 ? &v_array[p * num_comp] : tmp[(d + 1) % 2]));
1567               pre /= Q_1d;
1568               post *= 1;
1569             }
1570           }
1571           break;
1572         }
1573         case CEED_EVAL_GRAD: {
1574           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
1575 
1576           // ---- Values at point
1577           for (CeedInt p = 0; p < num_points; p++) {
1578             // Dim**2 contractions, apply grad when pass == dim
1579             for (CeedInt pass = dim - 1; pass >= 0; pass--) {
1580               CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
1581 
1582               for (CeedInt d = dim - 1; d >= 0; d--) {
1583                 const CeedScalar x = x_array_read[p * dim + d];
1584 
1585                 // ------ Compute Chebyshev polynomial values
1586                 if (pass == d) {
1587                   // chebyshev_temp holds the original series values
1588                   // chebyshev_x holds the derivative of the original series
1589                   CeedScalar chebyshev_temp[3];
1590 
1591                   chebyshev_temp[1] = 1.0;
1592                   chebyshev_temp[2] = 2 * x;
1593                   chebyshev_x[0]    = 0.0;
1594                   chebyshev_x[1]    = 2.0;
1595                   for (CeedInt j = 2; j < Q_1d; j++) {
1596                     chebyshev_temp[0] = chebyshev_temp[1];
1597                     chebyshev_temp[1] = chebyshev_temp[2];
1598                     chebyshev_temp[2] = 2 * x * chebyshev_temp[1] - chebyshev_temp[0];
1599                     chebyshev_x[j]    = 2 * x * chebyshev_x[j - 1] + 2 * chebyshev_temp[1] - chebyshev_x[j - 2];
1600                   }
1601                 } else {
1602                   chebyshev_x[0] = 1.0;
1603                   chebyshev_x[1] = 2 * x;
1604                   for (CeedInt j = 2; j < Q_1d; j++) chebyshev_x[j] = 2 * x * chebyshev_x[j - 1] - chebyshev_x[j - 2];
1605                 }
1606                 // ------ Tensor contract
1607                 CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
1608                                                  d == (dim - 1) ? chebyshev_coeffs : tmp[d % 2],
1609                                                  d == 0 ? &v_array[p * num_comp * dim + pass] : tmp[(d + 1) % 2]));
1610                 pre /= Q_1d;
1611                 post *= 1;
1612               }
1613             }
1614           }
1615           break;
1616         }
1617         default:
1618           // Nothing to do, this won't occur
1619           break;
1620       }
1621       CeedCall(CeedVectorRestoreArrayRead(basis->vec_chebyshev, &chebyshev_coeffs));
1622       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
1623       CeedCall(CeedVectorRestoreArray(v, &v_array));
1624       break;
1625     }
1626     case CEED_TRANSPOSE: {
1627       // Arbitrary points to nodes
1628       CeedScalar       *chebyshev_coeffs;
1629       const CeedScalar *u_array, *x_array_read;
1630 
1631       // -- Transpose of evaluaton of Chebyshev polynomials at arbitrary points
1632       CeedCall(CeedVectorGetArrayWrite(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
1633       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
1634       CeedCall(CeedVectorGetArrayRead(u, CEED_MEM_HOST, &u_array));
1635       {
1636         CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
1637 
1638         // ---- Values at point
1639         for (CeedInt p = 0; p < num_points; p++) {
1640           CeedInt pre = num_comp * 1, post = 1;
1641 
1642           for (CeedInt d = dim - 1; d >= 0; d--) {
1643             // ------ Compute Chebyshev polynomial values
1644             {
1645               const CeedScalar x = x_array_read[p * dim + d];
1646 
1647               chebyshev_x[0] = 1.0;
1648               chebyshev_x[1] = 2 * x;
1649               for (CeedInt j = 2; j < Q_1d; j++) chebyshev_x[j] = 2 * x * chebyshev_x[j - 1] - chebyshev_x[j - 2];
1650             }
1651             // ------ Tensor contract
1652             CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode, p > 0 && d == 0,
1653                                              d == (dim - 1) ? &u_array[p * num_comp] : tmp[d % 2], d == 0 ? chebyshev_coeffs : tmp[(d + 1) % 2]));
1654             pre /= 1;
1655             post *= Q_1d;
1656           }
1657         }
1658       }
1659       CeedCall(CeedVectorRestoreArray(basis->vec_chebyshev, &chebyshev_coeffs));
1660       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
1661       CeedCall(CeedVectorRestoreArrayRead(u, &u_array));
1662 
1663       // -- Interpolate transpose from Chebyshev coefficients
1664       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
1665       break;
1666     }
1667   }
1668 
1669   return CEED_ERROR_SUCCESS;
1670 }
1671 
1672 /**
1673   @brief Get Ceed associated with a CeedBasis
1674 
1675   @param[in]  basis CeedBasis
1676   @param[out] ceed  Variable to store Ceed
1677 
1678   @return An error code: 0 - success, otherwise - failure
1679 
1680   @ref Advanced
1681 **/
1682 int CeedBasisGetCeed(CeedBasis basis, Ceed *ceed) {
1683   *ceed = basis->ceed;
1684   return CEED_ERROR_SUCCESS;
1685 }
1686 
1687 /**
1688   @brief Get dimension for given CeedBasis
1689 
1690   @param[in]  basis CeedBasis
1691   @param[out] dim   Variable to store dimension of basis
1692 
1693   @return An error code: 0 - success, otherwise - failure
1694 
1695   @ref Advanced
1696 **/
1697 int CeedBasisGetDimension(CeedBasis basis, CeedInt *dim) {
1698   *dim = basis->dim;
1699   return CEED_ERROR_SUCCESS;
1700 }
1701 
1702 /**
1703   @brief Get topology for given CeedBasis
1704 
1705   @param[in]  basis CeedBasis
1706   @param[out] topo  Variable to store topology of basis
1707 
1708   @return An error code: 0 - success, otherwise - failure
1709 
1710   @ref Advanced
1711 **/
1712 int CeedBasisGetTopology(CeedBasis basis, CeedElemTopology *topo) {
1713   *topo = basis->topo;
1714   return CEED_ERROR_SUCCESS;
1715 }
1716 
1717 /**
1718   @brief Get number of components for given CeedBasis
1719 
1720   @param[in]  basis    CeedBasis
1721   @param[out] num_comp Variable to store number of components of basis
1722 
1723   @return An error code: 0 - success, otherwise - failure
1724 
1725   @ref Advanced
1726 **/
1727 int CeedBasisGetNumComponents(CeedBasis basis, CeedInt *num_comp) {
1728   *num_comp = basis->num_comp;
1729   return CEED_ERROR_SUCCESS;
1730 }
1731 
1732 /**
1733   @brief Get total number of nodes (in dim dimensions) of a CeedBasis
1734 
1735   @param[in]  basis CeedBasis
1736   @param[out] P     Variable to store number of nodes
1737 
1738   @return An error code: 0 - success, otherwise - failure
1739 
1740   @ref Utility
1741 **/
1742 int CeedBasisGetNumNodes(CeedBasis basis, CeedInt *P) {
1743   *P = basis->P;
1744   return CEED_ERROR_SUCCESS;
1745 }
1746 
1747 /**
1748   @brief Get total number of nodes (in 1 dimension) of a CeedBasis
1749 
1750   @param[in]  basis CeedBasis
1751   @param[out] P_1d  Variable to store number of nodes
1752 
1753   @return An error code: 0 - success, otherwise - failure
1754 
1755   @ref Advanced
1756 **/
1757 int CeedBasisGetNumNodes1D(CeedBasis basis, CeedInt *P_1d) {
1758   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "Cannot supply P_1d for non-tensor basis");
1759   *P_1d = basis->P_1d;
1760   return CEED_ERROR_SUCCESS;
1761 }
1762 
1763 /**
1764   @brief Get total number of quadrature points (in dim dimensions) of a CeedBasis
1765 
1766   @param[in]  basis CeedBasis
1767   @param[out] Q     Variable to store number of quadrature points
1768 
1769   @return An error code: 0 - success, otherwise - failure
1770 
1771   @ref Utility
1772 **/
1773 int CeedBasisGetNumQuadraturePoints(CeedBasis basis, CeedInt *Q) {
1774   *Q = basis->Q;
1775   return CEED_ERROR_SUCCESS;
1776 }
1777 
1778 /**
1779   @brief Get total number of quadrature points (in 1 dimension) of a CeedBasis
1780 
1781   @param[in]  basis CeedBasis
1782   @param[out] Q_1d  Variable to store number of quadrature points
1783 
1784   @return An error code: 0 - success, otherwise - failure
1785 
1786   @ref Advanced
1787 **/
1788 int CeedBasisGetNumQuadraturePoints1D(CeedBasis basis, CeedInt *Q_1d) {
1789   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "Cannot supply Q_1d for non-tensor basis");
1790   *Q_1d = basis->Q_1d;
1791   return CEED_ERROR_SUCCESS;
1792 }
1793 
1794 /**
1795   @brief Get reference coordinates of quadrature points (in dim dimensions) of a CeedBasis
1796 
1797   @param[in]  basis CeedBasis
1798   @param[out] q_ref Variable to store reference coordinates of quadrature points
1799 
1800   @return An error code: 0 - success, otherwise - failure
1801 
1802   @ref Advanced
1803 **/
1804 int CeedBasisGetQRef(CeedBasis basis, const CeedScalar **q_ref) {
1805   *q_ref = basis->q_ref_1d;
1806   return CEED_ERROR_SUCCESS;
1807 }
1808 
1809 /**
1810   @brief Get quadrature weights of quadrature points (in dim dimensions) of a CeedBasis
1811 
1812   @param[in]  basis    CeedBasis
1813   @param[out] q_weight Variable to store quadrature weights
1814 
1815   @return An error code: 0 - success, otherwise - failure
1816 
1817   @ref Advanced
1818 **/
1819 int CeedBasisGetQWeights(CeedBasis basis, const CeedScalar **q_weight) {
1820   *q_weight = basis->q_weight_1d;
1821   return CEED_ERROR_SUCCESS;
1822 }
1823 
1824 /**
1825   @brief Get interpolation matrix of a CeedBasis
1826 
1827   @param[in]  basis  CeedBasis
1828   @param[out] interp Variable to store interpolation matrix
1829 
1830   @return An error code: 0 - success, otherwise - failure
1831 
1832   @ref Advanced
1833 **/
1834 int CeedBasisGetInterp(CeedBasis basis, const CeedScalar **interp) {
1835   if (!basis->interp && basis->is_tensor_basis) {
1836     // Allocate
1837     CeedCall(CeedMalloc(basis->Q * basis->P, &basis->interp));
1838 
1839     // Initialize
1840     for (CeedInt i = 0; i < basis->Q * basis->P; i++) basis->interp[i] = 1.0;
1841 
1842     // Calculate
1843     for (CeedInt d = 0; d < basis->dim; d++) {
1844       for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
1845         for (CeedInt node = 0; node < basis->P; node++) {
1846           CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
1847           CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
1848           basis->interp[qpt * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
1849         }
1850       }
1851     }
1852   }
1853   *interp = basis->interp;
1854   return CEED_ERROR_SUCCESS;
1855 }
1856 
1857 /**
1858   @brief Get 1D interpolation matrix of a tensor product CeedBasis
1859 
1860   @param[in]  basis     CeedBasis
1861   @param[out] interp_1d Variable to store interpolation matrix
1862 
1863   @return An error code: 0 - success, otherwise - failure
1864 
1865   @ref Backend
1866 **/
1867 int CeedBasisGetInterp1D(CeedBasis basis, const CeedScalar **interp_1d) {
1868   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "CeedBasis is not a tensor product basis.");
1869   *interp_1d = basis->interp_1d;
1870   return CEED_ERROR_SUCCESS;
1871 }
1872 
1873 /**
1874   @brief Get gradient matrix of a CeedBasis
1875 
1876   @param[in]  basis CeedBasis
1877   @param[out] grad  Variable to store gradient matrix
1878 
1879   @return An error code: 0 - success, otherwise - failure
1880 
1881   @ref Advanced
1882 **/
1883 int CeedBasisGetGrad(CeedBasis basis, const CeedScalar **grad) {
1884   if (!basis->grad && basis->is_tensor_basis) {
1885     // Allocate
1886     CeedCall(CeedMalloc(basis->dim * basis->Q * basis->P, &basis->grad));
1887 
1888     // Initialize
1889     for (CeedInt i = 0; i < basis->dim * basis->Q * basis->P; i++) basis->grad[i] = 1.0;
1890 
1891     // Calculate
1892     for (CeedInt d = 0; d < basis->dim; d++) {
1893       for (CeedInt i = 0; i < basis->dim; i++) {
1894         for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
1895           for (CeedInt node = 0; node < basis->P; node++) {
1896             CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
1897             CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
1898             if (i == d) basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->grad_1d[q * basis->P_1d + p];
1899             else basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
1900           }
1901         }
1902       }
1903     }
1904   }
1905   *grad = basis->grad;
1906   return CEED_ERROR_SUCCESS;
1907 }
1908 
1909 /**
1910   @brief Get 1D gradient matrix of a tensor product CeedBasis
1911 
1912   @param[in]  basis   CeedBasis
1913   @param[out] grad_1d Variable to store gradient matrix
1914 
1915   @return An error code: 0 - success, otherwise - failure
1916 
1917   @ref Advanced
1918 **/
1919 int CeedBasisGetGrad1D(CeedBasis basis, const CeedScalar **grad_1d) {
1920   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "CeedBasis is not a tensor product basis.");
1921   *grad_1d = basis->grad_1d;
1922   return CEED_ERROR_SUCCESS;
1923 }
1924 
1925 /**
1926   @brief Get divergence matrix of a CeedBasis
1927 
1928   @param[in]  basis CeedBasis
1929   @param[out] div   Variable to store divergence matrix
1930 
1931   @return An error code: 0 - success, otherwise - failure
1932 
1933   @ref Advanced
1934 **/
1935 int CeedBasisGetDiv(CeedBasis basis, const CeedScalar **div) {
1936   CeedCheck(basis->div, basis->ceed, CEED_ERROR_MINOR, "CeedBasis does not have divergence matrix.");
1937   *div = basis->div;
1938   return CEED_ERROR_SUCCESS;
1939 }
1940 
1941 /**
1942   @brief Get curl matrix of a CeedBasis
1943 
1944   @param[in]  basis CeedBasis
1945   @param[out] curl  Variable to store curl matrix
1946 
1947   @return An error code: 0 - success, otherwise - failure
1948 
1949   @ref Advanced
1950 **/
1951 int CeedBasisGetCurl(CeedBasis basis, const CeedScalar **curl) {
1952   CeedCheck(basis->curl, basis->ceed, CEED_ERROR_MINOR, "CeedBasis does not have curl matrix.");
1953   *curl = basis->curl;
1954   return CEED_ERROR_SUCCESS;
1955 }
1956 
1957 /**
1958   @brief Destroy a CeedBasis
1959 
1960   @param[in,out] basis CeedBasis to destroy
1961 
1962   @return An error code: 0 - success, otherwise - failure
1963 
1964   @ref User
1965 **/
1966 int CeedBasisDestroy(CeedBasis *basis) {
1967   if (!*basis || *basis == CEED_BASIS_COLLOCATED || --(*basis)->ref_count > 0) {
1968     *basis = NULL;
1969     return CEED_ERROR_SUCCESS;
1970   }
1971   if ((*basis)->Destroy) CeedCall((*basis)->Destroy(*basis));
1972   CeedCall(CeedTensorContractDestroy(&(*basis)->contract));
1973   CeedCall(CeedFree(&(*basis)->q_ref_1d));
1974   CeedCall(CeedFree(&(*basis)->q_weight_1d));
1975   CeedCall(CeedFree(&(*basis)->interp));
1976   CeedCall(CeedFree(&(*basis)->interp_1d));
1977   CeedCall(CeedFree(&(*basis)->grad));
1978   CeedCall(CeedFree(&(*basis)->grad_1d));
1979   CeedCall(CeedFree(&(*basis)->div));
1980   CeedCall(CeedFree(&(*basis)->curl));
1981   CeedCall(CeedVectorDestroy(&(*basis)->vec_chebyshev));
1982   CeedCall(CeedBasisDestroy(&(*basis)->basis_chebyshev));
1983   CeedCall(CeedDestroy(&(*basis)->ceed));
1984   CeedCall(CeedFree(basis));
1985   return CEED_ERROR_SUCCESS;
1986 }
1987 
1988 /**
1989   @brief Construct a Gauss-Legendre quadrature
1990 
1991   @param[in]  Q           Number of quadrature points (integrates polynomials of degree 2*Q-1 exactly)
1992   @param[out] q_ref_1d    Array of length Q to hold the abscissa on [-1, 1]
1993   @param[out] q_weight_1d Array of length Q to hold the weights
1994 
1995   @return An error code: 0 - success, otherwise - failure
1996 
1997   @ref Utility
1998 **/
1999 int CeedGaussQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2000   // Allocate
2001   CeedScalar P0, P1, P2, dP2, xi, wi, PI = 4.0 * atan(1.0);
2002   // Build q_ref_1d, q_weight_1d
2003   for (CeedInt i = 0; i <= Q / 2; i++) {
2004     // Guess
2005     xi = cos(PI * (CeedScalar)(2 * i + 1) / ((CeedScalar)(2 * Q)));
2006     // Pn(xi)
2007     P0 = 1.0;
2008     P1 = xi;
2009     P2 = 0.0;
2010     for (CeedInt j = 2; j <= Q; j++) {
2011       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2012       P0 = P1;
2013       P1 = P2;
2014     }
2015     // First Newton Step
2016     dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2017     xi  = xi - P2 / dP2;
2018     // Newton to convergence
2019     for (CeedInt k = 0; k < 100 && fabs(P2) > 10 * CEED_EPSILON; k++) {
2020       P0 = 1.0;
2021       P1 = xi;
2022       for (CeedInt j = 2; j <= Q; j++) {
2023         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2024         P0 = P1;
2025         P1 = P2;
2026       }
2027       dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2028       xi  = xi - P2 / dP2;
2029     }
2030     // Save xi, wi
2031     wi                     = 2.0 / ((1.0 - xi * xi) * dP2 * dP2);
2032     q_weight_1d[i]         = wi;
2033     q_weight_1d[Q - 1 - i] = wi;
2034     q_ref_1d[i]            = -xi;
2035     q_ref_1d[Q - 1 - i]    = xi;
2036   }
2037   return CEED_ERROR_SUCCESS;
2038 }
2039 
2040 /**
2041   @brief Construct a Gauss-Legendre-Lobatto quadrature
2042 
2043   @param[in]  Q           Number of quadrature points (integrates polynomials of degree 2*Q-3 exactly)
2044   @param[out] q_ref_1d    Array of length Q to hold the abscissa on [-1, 1]
2045   @param[out] q_weight_1d Array of length Q to hold the weights
2046 
2047   @return An error code: 0 - success, otherwise - failure
2048 
2049   @ref Utility
2050 **/
2051 int CeedLobattoQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2052   // Allocate
2053   CeedScalar P0, P1, P2, dP2, d2P2, xi, wi, PI = 4.0 * atan(1.0);
2054   // Build q_ref_1d, q_weight_1d
2055   // Set endpoints
2056   CeedCheck(Q > 1, NULL, CEED_ERROR_DIMENSION, "Cannot create Lobatto quadrature with Q=%" CeedInt_FMT " < 2 points", Q);
2057   wi = 2.0 / ((CeedScalar)(Q * (Q - 1)));
2058   if (q_weight_1d) {
2059     q_weight_1d[0]     = wi;
2060     q_weight_1d[Q - 1] = wi;
2061   }
2062   q_ref_1d[0]     = -1.0;
2063   q_ref_1d[Q - 1] = 1.0;
2064   // Interior
2065   for (CeedInt i = 1; i <= (Q - 1) / 2; i++) {
2066     // Guess
2067     xi = cos(PI * (CeedScalar)(i) / (CeedScalar)(Q - 1));
2068     // Pn(xi)
2069     P0 = 1.0;
2070     P1 = xi;
2071     P2 = 0.0;
2072     for (CeedInt j = 2; j < Q; j++) {
2073       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2074       P0 = P1;
2075       P1 = P2;
2076     }
2077     // First Newton step
2078     dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2079     d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2080     xi   = xi - dP2 / d2P2;
2081     // Newton to convergence
2082     for (CeedInt k = 0; k < 100 && fabs(dP2) > 10 * CEED_EPSILON; k++) {
2083       P0 = 1.0;
2084       P1 = xi;
2085       for (CeedInt j = 2; j < Q; j++) {
2086         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2087         P0 = P1;
2088         P1 = P2;
2089       }
2090       dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2091       d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2092       xi   = xi - dP2 / d2P2;
2093     }
2094     // Save xi, wi
2095     wi = 2.0 / (((CeedScalar)(Q * (Q - 1))) * P2 * P2);
2096     if (q_weight_1d) {
2097       q_weight_1d[i]         = wi;
2098       q_weight_1d[Q - 1 - i] = wi;
2099     }
2100     q_ref_1d[i]         = -xi;
2101     q_ref_1d[Q - 1 - i] = xi;
2102   }
2103   return CEED_ERROR_SUCCESS;
2104 }
2105 
2106 /// @}
2107