xref: /libCEED/interface/ceed-basis.c (revision 93639ffbf2bbfa4b6788194663945beabeb0bf2d)
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_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    is_tensor_to, is_tensor_from;
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, "Bases must have compatible quadrature spaces");
207   Q = Q_to;
208 
209   // Check for matching tensor or non-tensor
210   CeedCall(CeedBasisIsTensor(basis_to, &is_tensor_to));
211   CeedCall(CeedBasisIsTensor(basis_from, &is_tensor_from));
212   CeedCheck(is_tensor_to == is_tensor_from, ceed, CEED_ERROR_MINOR, "Bases must both be tensor or non-tensor");
213   if (is_tensor_to) {
214     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_to));
215     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_from));
216     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis_from, &Q));
217   } else {
218     CeedCall(CeedBasisGetNumNodes(basis_to, &P_to));
219     CeedCall(CeedBasisGetNumNodes(basis_from, &P_from));
220   }
221 
222   // Check for matching FE space
223   CeedFESpace fe_space_to, fe_space_from;
224   CeedCall(CeedBasisGetFESpace(basis_to, &fe_space_to));
225   CeedCall(CeedBasisGetFESpace(basis_from, &fe_space_from));
226   CeedCheck(fe_space_to == fe_space_from, ceed, CEED_ERROR_MINOR, "Bases must both be the same FE space type");
227 
228   // Get source matrices
229   CeedInt           dim, q_comp = 1;
230   CeedScalar       *interp_to_inv, *interp_from;
231   const CeedScalar *interp_to_source = NULL, *interp_from_source = NULL, *grad_from_source = NULL;
232 
233   CeedCall(CeedBasisGetDimension(basis_to, &dim));
234   if (is_tensor_to) {
235     CeedCall(CeedBasisGetInterp1D(basis_to, &interp_to_source));
236     CeedCall(CeedBasisGetInterp1D(basis_from, &interp_from_source));
237   } else {
238     CeedCall(CeedBasisGetNumQuadratureComponents(basis_from, CEED_EVAL_INTERP, &q_comp));
239     CeedCall(CeedBasisGetInterp(basis_to, &interp_to_source));
240     CeedCall(CeedBasisGetInterp(basis_from, &interp_from_source));
241   }
242   CeedCall(CeedMalloc(Q * P_from * q_comp, &interp_from));
243   CeedCall(CeedCalloc(P_to * P_from, interp_project));
244 
245   // `grad_project = interp_to^+ * grad_from` is computed for the H^1 space case so the
246   // projection basis will have a gradient operation (allocated even if not H^1 for the
247   // basis construction later on)
248   if (fe_space_to == CEED_FE_SPACE_H1) {
249     if (is_tensor_to) {
250       CeedCall(CeedBasisGetGrad1D(basis_from, &grad_from_source));
251     } else {
252       CeedCall(CeedBasisGetGrad(basis_from, &grad_from_source));
253     }
254   }
255   CeedCall(CeedCalloc(P_to * P_from * (is_tensor_to ? 1 : dim), grad_project));
256 
257   // Compute interp_to^+, pseudoinverse of interp_to
258   CeedCall(CeedCalloc(Q * q_comp * P_to, &interp_to_inv));
259   CeedCall(CeedMatrixPseudoinverse(ceed, (CeedScalar *)interp_to_source, Q * q_comp, P_to, interp_to_inv));
260   // Build matrices
261   CeedInt     num_matrices = 1 + (fe_space_to == CEED_FE_SPACE_H1) * (is_tensor_to ? 1 : dim);
262   CeedScalar *input_from[num_matrices], *output_project[num_matrices];
263 
264   input_from[0]     = (CeedScalar *)interp_from_source;
265   output_project[0] = *interp_project;
266   for (CeedInt m = 1; m < num_matrices; m++) {
267     input_from[m]     = (CeedScalar *)&grad_from_source[(m - 1) * Q * P_from];
268     output_project[m] = &((*grad_project)[(m - 1) * P_to * P_from]);
269   }
270   for (CeedInt m = 0; m < num_matrices; m++) {
271     // output_project = interp_to^+ * interp_from
272     memcpy(interp_from, input_from[m], Q * P_from * q_comp * sizeof(input_from[m][0]));
273     CeedCall(CeedMatrixMatrixMultiply(ceed, interp_to_inv, input_from[m], output_project[m], P_to, P_from, Q * q_comp));
274     // Round zero to machine precision
275     for (CeedInt i = 0; i < P_to * P_from; i++) {
276       if (fabs(output_project[m][i]) < 10 * CEED_EPSILON) output_project[m][i] = 0.0;
277     }
278   }
279 
280   // Cleanup
281   CeedCall(CeedFree(&interp_to_inv));
282   CeedCall(CeedFree(&interp_from));
283   return CEED_ERROR_SUCCESS;
284 }
285 
286 /// @}
287 
288 /// ----------------------------------------------------------------------------
289 /// Ceed Backend API
290 /// ----------------------------------------------------------------------------
291 /// @addtogroup CeedBasisBackend
292 /// @{
293 
294 /**
295   @brief Return collocated gradient matrix
296 
297   @param[in]  basis         `CeedBasis`
298   @param[out] collo_grad_1d Row-major (`Q_1d * Q_1d`) matrix expressing derivatives of basis functions at quadrature points
299 
300   @return An error code: 0 - success, otherwise - failure
301 
302   @ref Backend
303 **/
304 int CeedBasisGetCollocatedGrad(CeedBasis basis, CeedScalar *collo_grad_1d) {
305   Ceed        ceed;
306   CeedInt     P_1d, Q_1d;
307   CeedScalar *interp_1d_pinv;
308   // Note: This function is for backend use, so all errors are terminal and we do not need to clean up memory on failure.
309   CeedCall(CeedBasisGetCeed(basis, &ceed));
310   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
311   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
312 
313   // Compute interp_1d^+, pseudoinverse of interp_1d
314   CeedCall(CeedCalloc(P_1d * Q_1d, &interp_1d_pinv));
315 
316   CeedCall(CeedMatrixPseudoinverse(ceed, basis->interp_1d, Q_1d, P_1d, interp_1d_pinv));
317   CeedCall(CeedMatrixMatrixMultiply(ceed, basis->grad_1d, (const CeedScalar *)interp_1d_pinv, collo_grad_1d, Q_1d, Q_1d, P_1d));
318 
319   CeedCall(CeedFree(&interp_1d_pinv));
320   return CEED_ERROR_SUCCESS;
321 }
322 
323 /**
324   @brief Get tensor status for given `CeedBasis`
325 
326   @param[in]  basis     `CeedBasis`
327   @param[out] is_tensor Variable to store tensor status
328 
329   @return An error code: 0 - success, otherwise - failure
330 
331   @ref Backend
332 **/
333 int CeedBasisIsTensor(CeedBasis basis, bool *is_tensor) {
334   *is_tensor = basis->is_tensor_basis;
335   return CEED_ERROR_SUCCESS;
336 }
337 
338 /**
339   @brief Get backend data of a `CeedBasis`
340 
341   @param[in]  basis `CeedBasis`
342   @param[out] data  Variable to store data
343 
344   @return An error code: 0 - success, otherwise - failure
345 
346   @ref Backend
347 **/
348 int CeedBasisGetData(CeedBasis basis, void *data) {
349   *(void **)data = basis->data;
350   return CEED_ERROR_SUCCESS;
351 }
352 
353 /**
354   @brief Set backend data of a `CeedBasis`
355 
356   @param[in,out] basis  `CeedBasis`
357   @param[in]     data   Data to set
358 
359   @return An error code: 0 - success, otherwise - failure
360 
361   @ref Backend
362 **/
363 int CeedBasisSetData(CeedBasis basis, void *data) {
364   basis->data = data;
365   return CEED_ERROR_SUCCESS;
366 }
367 
368 /**
369   @brief Increment the reference counter for a `CeedBasis`
370 
371   @param[in,out] basis `CeedBasis` to increment the reference counter
372 
373   @return An error code: 0 - success, otherwise - failure
374 
375   @ref Backend
376 **/
377 int CeedBasisReference(CeedBasis basis) {
378   basis->ref_count++;
379   return CEED_ERROR_SUCCESS;
380 }
381 
382 /**
383   @brief Get number of Q-vector components for given `CeedBasis`
384 
385   @param[in]  basis     `CeedBasis`
386   @param[in]  eval_mode @ref CEED_EVAL_INTERP to use interpolated values,
387                           @ref CEED_EVAL_GRAD to use gradients,
388                           @ref CEED_EVAL_DIV to use divergence,
389                           @ref CEED_EVAL_CURL to use curl
390   @param[out] q_comp    Variable to store number of Q-vector components of basis
391 
392   @return An error code: 0 - success, otherwise - failure
393 
394   @ref Backend
395 **/
396 int CeedBasisGetNumQuadratureComponents(CeedBasis basis, CeedEvalMode eval_mode, CeedInt *q_comp) {
397   switch (eval_mode) {
398     case CEED_EVAL_INTERP:
399       *q_comp = (basis->fe_space == CEED_FE_SPACE_H1) ? 1 : basis->dim;
400       break;
401     case CEED_EVAL_GRAD:
402       *q_comp = basis->dim;
403       break;
404     case CEED_EVAL_DIV:
405       *q_comp = 1;
406       break;
407     case CEED_EVAL_CURL:
408       *q_comp = (basis->dim < 3) ? 1 : basis->dim;
409       break;
410     case CEED_EVAL_NONE:
411     case CEED_EVAL_WEIGHT:
412       *q_comp = 1;
413       break;
414   }
415   return CEED_ERROR_SUCCESS;
416 }
417 
418 /**
419   @brief Estimate number of FLOPs required to apply `CeedBasis` in `t_mode` and `eval_mode`
420 
421   @param[in]  basis     `CeedBasis` to estimate FLOPs for
422   @param[in]  t_mode    Apply basis or transpose
423   @param[in]  eval_mode @ref CeedEvalMode
424   @param[out] flops     Address of variable to hold FLOPs estimate
425 
426   @ref Backend
427 **/
428 int CeedBasisGetFlopsEstimate(CeedBasis basis, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedSize *flops) {
429   bool is_tensor;
430 
431   CeedCall(CeedBasisIsTensor(basis, &is_tensor));
432   if (is_tensor) {
433     CeedInt dim, num_comp, P_1d, Q_1d;
434 
435     CeedCall(CeedBasisGetDimension(basis, &dim));
436     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
437     CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
438     CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
439     if (t_mode == CEED_TRANSPOSE) {
440       P_1d = Q_1d;
441       Q_1d = P_1d;
442     }
443     CeedInt tensor_flops = 0, pre = num_comp * CeedIntPow(P_1d, dim - 1), post = 1;
444     for (CeedInt d = 0; d < dim; d++) {
445       tensor_flops += 2 * pre * P_1d * post * Q_1d;
446       pre /= P_1d;
447       post *= Q_1d;
448     }
449     switch (eval_mode) {
450       case CEED_EVAL_NONE:
451         *flops = 0;
452         break;
453       case CEED_EVAL_INTERP:
454         *flops = tensor_flops;
455         break;
456       case CEED_EVAL_GRAD:
457         *flops = tensor_flops * 2;
458         break;
459       case CEED_EVAL_DIV:
460       case CEED_EVAL_CURL:
461         // LCOV_EXCL_START
462         return CeedError(basis->ceed, CEED_ERROR_INCOMPATIBLE, "Tensor basis evaluation for %s not supported", CeedEvalModes[eval_mode]);
463         break;
464       // LCOV_EXCL_STOP
465       case CEED_EVAL_WEIGHT:
466         *flops = dim * CeedIntPow(Q_1d, dim);
467         break;
468     }
469   } else {
470     CeedInt dim, num_comp, q_comp, num_nodes, num_qpts;
471 
472     CeedCall(CeedBasisGetDimension(basis, &dim));
473     CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
474     CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
475     CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
476     CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
477     switch (eval_mode) {
478       case CEED_EVAL_NONE:
479         *flops = 0;
480         break;
481       case CEED_EVAL_INTERP:
482       case CEED_EVAL_GRAD:
483       case CEED_EVAL_DIV:
484       case CEED_EVAL_CURL:
485         *flops = num_nodes * num_qpts * num_comp * q_comp;
486         break;
487       case CEED_EVAL_WEIGHT:
488         *flops = 0;
489         break;
490     }
491   }
492   return CEED_ERROR_SUCCESS;
493 }
494 
495 /**
496   @brief Get `CeedFESpace` for a `CeedBasis`
497 
498   @param[in]  basis    `CeedBasis`
499   @param[out] fe_space Variable to store `CeedFESpace`
500 
501   @return An error code: 0 - success, otherwise - failure
502 
503   @ref Backend
504 **/
505 int CeedBasisGetFESpace(CeedBasis basis, CeedFESpace *fe_space) {
506   *fe_space = basis->fe_space;
507   return CEED_ERROR_SUCCESS;
508 }
509 
510 /**
511   @brief Get dimension for given `CeedElemTopology`
512 
513   @param[in]  topo `CeedElemTopology`
514   @param[out] dim  Variable to store dimension of topology
515 
516   @return An error code: 0 - success, otherwise - failure
517 
518   @ref Backend
519 **/
520 int CeedBasisGetTopologyDimension(CeedElemTopology topo, CeedInt *dim) {
521   *dim = (CeedInt)topo >> 16;
522   return CEED_ERROR_SUCCESS;
523 }
524 
525 /**
526   @brief Get `CeedTensorContract` of a `CeedBasis`
527 
528   @param[in]  basis     `CeedBasis`
529   @param[out] contract  Variable to store `CeedTensorContract`
530 
531   @return An error code: 0 - success, otherwise - failure
532 
533   @ref Backend
534 **/
535 int CeedBasisGetTensorContract(CeedBasis basis, CeedTensorContract *contract) {
536   *contract = basis->contract;
537   return CEED_ERROR_SUCCESS;
538 }
539 
540 /**
541   @brief Set `CeedTensorContract` of a `CeedBasis`
542 
543   @param[in,out] basis    `CeedBasis`
544   @param[in]     contract `CeedTensorContract` to set
545 
546   @return An error code: 0 - success, otherwise - failure
547 
548   @ref Backend
549 **/
550 int CeedBasisSetTensorContract(CeedBasis basis, CeedTensorContract contract) {
551   basis->contract = contract;
552   CeedCall(CeedTensorContractReference(contract));
553   return CEED_ERROR_SUCCESS;
554 }
555 
556 /**
557   @brief Return a reference implementation of matrix multiplication \f$C = A B\f$.
558 
559   Note: This is a reference implementation for CPU `CeedScalar` pointers that is not intended for high performance.
560 
561   @param[in]  ceed  `Ceed` context for error handling
562   @param[in]  mat_A Row-major matrix `A`
563   @param[in]  mat_B Row-major matrix `B`
564   @param[out] mat_C Row-major output matrix `C`
565   @param[in]  m     Number of rows of `C`
566   @param[in]  n     Number of columns of `C`
567   @param[in]  kk    Number of columns of `A`/rows of `B`
568 
569   @return An error code: 0 - success, otherwise - failure
570 
571   @ref Utility
572 **/
573 int CeedMatrixMatrixMultiply(Ceed ceed, const CeedScalar *mat_A, const CeedScalar *mat_B, CeedScalar *mat_C, CeedInt m, CeedInt n, CeedInt kk) {
574   for (CeedInt i = 0; i < m; i++) {
575     for (CeedInt j = 0; j < n; j++) {
576       CeedScalar sum = 0;
577 
578       for (CeedInt k = 0; k < kk; k++) sum += mat_A[k + i * kk] * mat_B[j + k * n];
579       mat_C[j + i * n] = sum;
580     }
581   }
582   return CEED_ERROR_SUCCESS;
583 }
584 
585 /**
586   @brief Return QR Factorization of a matrix
587 
588   @param[in]     ceed `Ceed` context for error handling
589   @param[in,out] mat  Row-major matrix to be factorized in place
590   @param[in,out] tau  Vector of length `m` of scaling factors
591   @param[in]     m    Number of rows
592   @param[in]     n    Number of columns
593 
594   @return An error code: 0 - success, otherwise - failure
595 
596   @ref Utility
597 **/
598 int CeedQRFactorization(Ceed ceed, CeedScalar *mat, CeedScalar *tau, CeedInt m, CeedInt n) {
599   CeedScalar v[m];
600 
601   // Check matrix shape
602   CeedCheck(n <= m, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute QR factorization with n > m");
603 
604   for (CeedInt i = 0; i < n; i++) {
605     CeedScalar sigma = 0.0;
606 
607     if (i >= m - 1) {  // last row of matrix, no reflection needed
608       tau[i] = 0.;
609       break;
610     }
611     // Calculate Householder vector, magnitude
612     v[i] = mat[i + n * i];
613     for (CeedInt j = i + 1; j < m; j++) {
614       v[j] = mat[i + n * j];
615       sigma += v[j] * v[j];
616     }
617     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:m]
618     const CeedScalar R_ii = -copysign(norm, v[i]);
619 
620     v[i] -= R_ii;
621     // norm of v[i:m] after modification above and scaling below
622     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
623     //   tau = 2 / (norm*norm)
624     tau[i] = 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
625     for (CeedInt j = i + 1; j < m; j++) v[j] /= v[i];
626 
627     // Apply Householder reflector to lower right panel
628     CeedHouseholderReflect(&mat[i * n + i + 1], &v[i], tau[i], m - i, n - i - 1, n, 1);
629     // Save v
630     mat[i + n * i] = R_ii;
631     for (CeedInt j = i + 1; j < m; j++) mat[i + n * j] = v[j];
632   }
633   return CEED_ERROR_SUCCESS;
634 }
635 
636 /**
637   @brief Apply Householder Q matrix
638 
639   Compute `mat_A = mat_Q mat_A`, where `mat_Q` is \f$m \times m\f$ and `mat_A` is \f$m \times n\f$.
640 
641   @param[in,out] mat_A  Matrix to apply Householder Q to, in place
642   @param[in]     mat_Q  Householder Q matrix
643   @param[in]     tau    Householder scaling factors
644   @param[in]     t_mode Transpose mode for application
645   @param[in]     m      Number of rows in `A`
646   @param[in]     n      Number of columns in `A`
647   @param[in]     k      Number of elementary reflectors in Q, `k < m`
648   @param[in]     row    Row stride in `A`
649   @param[in]     col    Col stride in `A`
650 
651   @return An error code: 0 - success, otherwise - failure
652 
653   @ref Utility
654 **/
655 int CeedHouseholderApplyQ(CeedScalar *mat_A, const CeedScalar *mat_Q, const CeedScalar *tau, CeedTransposeMode t_mode, CeedInt m, CeedInt n,
656                           CeedInt k, CeedInt row, CeedInt col) {
657   CeedScalar *v;
658 
659   CeedCall(CeedMalloc(m, &v));
660   for (CeedInt ii = 0; ii < k; ii++) {
661     CeedInt i = t_mode == CEED_TRANSPOSE ? ii : k - 1 - ii;
662     for (CeedInt j = i + 1; j < m; j++) v[j] = mat_Q[j * k + i];
663     // Apply Householder reflector (I - tau v v^T) collo_grad_1d^T
664     CeedCall(CeedHouseholderReflect(&mat_A[i * row], &v[i], tau[i], m - i, n, row, col));
665   }
666   CeedCall(CeedFree(&v));
667   return CEED_ERROR_SUCCESS;
668 }
669 
670 /**
671   @brief Return pseudoinverse of a matrix
672 
673   @param[in]     ceed      Ceed context for error handling
674   @param[in]     mat       Row-major matrix to compute pseudoinverse of
675   @param[in]     m         Number of rows
676   @param[in]     n         Number of columns
677   @param[out]    mat_pinv  Row-major pseudoinverse matrix
678 
679   @return An error code: 0 - success, otherwise - failure
680 
681   @ref Utility
682 **/
683 int CeedMatrixPseudoinverse(Ceed ceed, CeedScalar *mat, CeedInt m, CeedInt n, CeedScalar *mat_pinv) {
684   CeedScalar *tau, *I, *mat_copy;
685 
686   CeedCall(CeedCalloc(m, &tau));
687   CeedCall(CeedCalloc(m * m, &I));
688   CeedCall(CeedCalloc(m * n, &mat_copy));
689   memcpy(mat_copy, mat, m * n * sizeof mat[0]);
690 
691   // QR Factorization, mat = Q R
692   CeedCall(CeedQRFactorization(ceed, mat_copy, tau, m, n));
693 
694   // -- Apply Q^T, I = Q^T * I
695   for (CeedInt i = 0; i < m; i++) I[i * m + i] = 1.0;
696   CeedCall(CeedHouseholderApplyQ(I, mat_copy, tau, CEED_TRANSPOSE, m, m, n, m, 1));
697   // -- Apply R_inv, mat_pinv = R_inv * Q^T
698   for (CeedInt j = 0; j < m; j++) {  // Column j
699     mat_pinv[j + m * (n - 1)] = I[j + m * (n - 1)] / mat_copy[n * n - 1];
700     for (CeedInt i = n - 2; i >= 0; i--) {  // Row i
701       mat_pinv[j + m * i] = I[j + m * i];
702       for (CeedInt k = i + 1; k < n; k++) mat_pinv[j + m * i] -= mat_copy[k + n * i] * mat_pinv[j + m * k];
703       mat_pinv[j + m * i] /= mat_copy[i + n * i];
704     }
705   }
706 
707   // Cleanup
708   CeedCall(CeedFree(&I));
709   CeedCall(CeedFree(&tau));
710   CeedCall(CeedFree(&mat_copy));
711   return CEED_ERROR_SUCCESS;
712 }
713 
714 /**
715   @brief Return symmetric Schur decomposition of the symmetric matrix mat via symmetric QR factorization
716 
717   @param[in]     ceed   `Ceed` context for error handling
718   @param[in,out] mat    Row-major matrix to be factorized in place
719   @param[out]    lambda Vector of length n of eigenvalues
720   @param[in]     n      Number of rows/columns
721 
722   @return An error code: 0 - success, otherwise - failure
723 
724   @ref Utility
725 **/
726 CeedPragmaOptimizeOff
727 int CeedSymmetricSchurDecomposition(Ceed ceed, CeedScalar *mat, CeedScalar *lambda, CeedInt n) {
728   // Check bounds for clang-tidy
729   CeedCheck(n > 1, ceed, CEED_ERROR_UNSUPPORTED, "Cannot compute symmetric Schur decomposition of scalars");
730 
731   CeedScalar v[n - 1], tau[n - 1], mat_T[n * n];
732 
733   // Copy mat to mat_T and set mat to I
734   memcpy(mat_T, mat, n * n * sizeof(mat[0]));
735   for (CeedInt i = 0; i < n; i++) {
736     for (CeedInt j = 0; j < n; j++) mat[j + n * i] = (i == j) ? 1 : 0;
737   }
738 
739   // Reduce to tridiagonal
740   for (CeedInt i = 0; i < n - 1; i++) {
741     // Calculate Householder vector, magnitude
742     CeedScalar sigma = 0.0;
743 
744     v[i] = mat_T[i + n * (i + 1)];
745     for (CeedInt j = i + 1; j < n - 1; j++) {
746       v[j] = mat_T[i + n * (j + 1)];
747       sigma += v[j] * v[j];
748     }
749     const CeedScalar norm = sqrt(v[i] * v[i] + sigma);  // norm of v[i:n-1]
750     const CeedScalar R_ii = -copysign(norm, v[i]);
751 
752     v[i] -= R_ii;
753     // norm of v[i:m] after modification above and scaling below
754     //   norm = sqrt(v[i]*v[i] + sigma) / v[i];
755     //   tau = 2 / (norm*norm)
756     tau[i] = i == n - 2 ? 2 : 2 * v[i] * v[i] / (v[i] * v[i] + sigma);
757     for (CeedInt j = i + 1; j < n - 1; j++) v[j] /= v[i];
758 
759     // Update sub and super diagonal
760     for (CeedInt j = i + 2; j < n; j++) {
761       mat_T[i + n * j] = 0;
762       mat_T[j + n * i] = 0;
763     }
764     // Apply symmetric Householder reflector to lower right panel
765     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
766     CeedHouseholderReflect(&mat_T[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), 1, n);
767 
768     // Save v
769     mat_T[i + n * (i + 1)] = R_ii;
770     mat_T[(i + 1) + n * i] = R_ii;
771     for (CeedInt j = i + 1; j < n - 1; j++) {
772       mat_T[i + n * (j + 1)] = v[j];
773     }
774   }
775   // Backwards accumulation of Q
776   for (CeedInt i = n - 2; i >= 0; i--) {
777     if (tau[i] > 0.0) {
778       v[i] = 1;
779       for (CeedInt j = i + 1; j < n - 1; j++) {
780         v[j]                   = mat_T[i + n * (j + 1)];
781         mat_T[i + n * (j + 1)] = 0;
782       }
783       CeedHouseholderReflect(&mat[(i + 1) + n * (i + 1)], &v[i], tau[i], n - (i + 1), n - (i + 1), n, 1);
784     }
785   }
786 
787   // Reduce sub and super diagonal
788   CeedInt    p = 0, q = 0, itr = 0, max_itr = n * n * n * n;
789   CeedScalar tol = CEED_EPSILON;
790 
791   while (itr < max_itr) {
792     // Update p, q, size of reduced portions of diagonal
793     p = 0;
794     q = 0;
795     for (CeedInt i = n - 2; i >= 0; i--) {
796       if (fabs(mat_T[i + n * (i + 1)]) < tol) q += 1;
797       else break;
798     }
799     for (CeedInt i = 0; i < n - q - 1; i++) {
800       if (fabs(mat_T[i + n * (i + 1)]) < tol) p += 1;
801       else break;
802     }
803     if (q == n - 1) break;  // Finished reducing
804 
805     // Reduce tridiagonal portion
806     CeedScalar t_nn = mat_T[(n - 1 - q) + n * (n - 1 - q)], t_nnm1 = mat_T[(n - 2 - q) + n * (n - 1 - q)];
807     CeedScalar d  = (mat_T[(n - 2 - q) + n * (n - 2 - q)] - t_nn) / 2;
808     CeedScalar mu = t_nn - t_nnm1 * t_nnm1 / (d + copysign(sqrt(d * d + t_nnm1 * t_nnm1), d));
809     CeedScalar x  = mat_T[p + n * p] - mu;
810     CeedScalar z  = mat_T[p + n * (p + 1)];
811 
812     for (CeedInt k = p; k < n - q - 1; k++) {
813       // Compute Givens rotation
814       CeedScalar c = 1, s = 0;
815 
816       if (fabs(z) > tol) {
817         if (fabs(z) > fabs(x)) {
818           const CeedScalar tau = -x / z;
819 
820           s = 1 / sqrt(1 + tau * tau);
821           c = s * tau;
822         } else {
823           const CeedScalar tau = -z / x;
824 
825           c = 1 / sqrt(1 + tau * tau);
826           s = c * tau;
827         }
828       }
829 
830       // Apply Givens rotation to T
831       CeedGivensRotation(mat_T, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
832       CeedGivensRotation(mat_T, c, s, CEED_TRANSPOSE, k, k + 1, n, n);
833 
834       // Apply Givens rotation to Q
835       CeedGivensRotation(mat, c, s, CEED_NOTRANSPOSE, k, k + 1, n, n);
836 
837       // Update x, z
838       if (k < n - q - 2) {
839         x = mat_T[k + n * (k + 1)];
840         z = mat_T[k + n * (k + 2)];
841       }
842     }
843     itr++;
844   }
845 
846   // Save eigenvalues
847   for (CeedInt i = 0; i < n; i++) lambda[i] = mat_T[i + n * i];
848 
849   // Check convergence
850   CeedCheck(itr < max_itr || q > n, ceed, CEED_ERROR_MINOR, "Symmetric QR failed to converge");
851   return CEED_ERROR_SUCCESS;
852 }
853 CeedPragmaOptimizeOn
854 
855 /**
856   @brief Return Simultaneous Diagonalization of two matrices.
857 
858   This solves the generalized eigenvalue problem `A x = lambda B x`, where `A` and `B` are symmetric and `B` is positive definite.
859   We generate the matrix `X` and vector `Lambda` such that `X^T A X = Lambda` and `X^T B X = I`.
860   This is equivalent to the LAPACK routine 'sygv' with `TYPE = 1`.
861 
862   @param[in]  ceed   `Ceed` context for error handling
863   @param[in]  mat_A  Row-major matrix to be factorized with eigenvalues
864   @param[in]  mat_B  Row-major matrix to be factorized to identity
865   @param[out] mat_X  Row-major orthogonal matrix
866   @param[out] lambda Vector of length `n` of generalized eigenvalues
867   @param[in]  n      Number of rows/columns
868 
869   @return An error code: 0 - success, otherwise - failure
870 
871   @ref Utility
872 **/
873 CeedPragmaOptimizeOff
874 int CeedSimultaneousDiagonalization(Ceed ceed, CeedScalar *mat_A, CeedScalar *mat_B, CeedScalar *mat_X, CeedScalar *lambda, CeedInt n) {
875   CeedScalar *mat_C, *mat_G, *vec_D;
876 
877   CeedCall(CeedCalloc(n * n, &mat_C));
878   CeedCall(CeedCalloc(n * n, &mat_G));
879   CeedCall(CeedCalloc(n, &vec_D));
880 
881   // Compute B = G D G^T
882   memcpy(mat_G, mat_B, n * n * sizeof(mat_B[0]));
883   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_G, vec_D, n));
884 
885   // Sort eigenvalues
886   for (CeedInt i = n - 1; i >= 0; i--) {
887     for (CeedInt j = 0; j < i; j++) {
888       if (fabs(vec_D[j]) > fabs(vec_D[j + 1])) {
889         CeedScalarSwap(vec_D[j], vec_D[j + 1]);
890         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_G[k * n + j], mat_G[k * n + j + 1]);
891       }
892     }
893   }
894 
895   // Compute C = (G D^1/2)^-1 A (G D^1/2)^-T
896   //           = D^-1/2 G^T A G D^-1/2
897   // -- D = D^-1/2
898   for (CeedInt i = 0; i < n; i++) vec_D[i] = 1. / sqrt(vec_D[i]);
899   // -- G = G D^-1/2
900   // -- C = D^-1/2 G^T
901   for (CeedInt i = 0; i < n; i++) {
902     for (CeedInt j = 0; j < n; j++) {
903       mat_G[i * n + j] *= vec_D[j];
904       mat_C[j * n + i] = mat_G[i * n + j];
905     }
906   }
907   // -- X = (D^-1/2 G^T) A
908   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_C, (const CeedScalar *)mat_A, mat_X, n, n, n));
909   // -- C = (D^-1/2 G^T A) (G D^-1/2)
910   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_X, (const CeedScalar *)mat_G, mat_C, n, n, n));
911 
912   // Compute Q^T C Q = lambda
913   CeedCall(CeedSymmetricSchurDecomposition(ceed, mat_C, lambda, n));
914 
915   // Sort eigenvalues
916   for (CeedInt i = n - 1; i >= 0; i--) {
917     for (CeedInt j = 0; j < i; j++) {
918       if (fabs(lambda[j]) > fabs(lambda[j + 1])) {
919         CeedScalarSwap(lambda[j], lambda[j + 1]);
920         for (CeedInt k = 0; k < n; k++) CeedScalarSwap(mat_C[k * n + j], mat_C[k * n + j + 1]);
921       }
922     }
923   }
924 
925   // Set X = (G D^1/2)^-T Q
926   //       = G D^-1/2 Q
927   CeedCall(CeedMatrixMatrixMultiply(ceed, (const CeedScalar *)mat_G, (const CeedScalar *)mat_C, mat_X, n, n, n));
928 
929   // Cleanup
930   CeedCall(CeedFree(&mat_C));
931   CeedCall(CeedFree(&mat_G));
932   CeedCall(CeedFree(&vec_D));
933   return CEED_ERROR_SUCCESS;
934 }
935 CeedPragmaOptimizeOn
936 
937 /// @}
938 
939 /// ----------------------------------------------------------------------------
940 /// CeedBasis Public API
941 /// ----------------------------------------------------------------------------
942 /// @addtogroup CeedBasisUser
943 /// @{
944 
945 /**
946   @brief Create a tensor-product basis for \f$H^1\f$ discretizations
947 
948   @param[in]  ceed        `Ceed` object used to create the `CeedBasis`
949   @param[in]  dim         Topological dimension
950   @param[in]  num_comp    Number of field components (1 for scalar fields)
951   @param[in]  P_1d        Number of nodes in one dimension
952   @param[in]  Q_1d        Number of quadrature points in one dimension
953   @param[in]  interp_1d   Row-major (`Q_1d * P_1d`) matrix expressing the values of nodal basis functions at quadrature points
954   @param[in]  grad_1d     Row-major (`Q_1d * P_1d`) matrix expressing derivatives of nodal basis functions at quadrature points
955   @param[in]  q_ref_1d    Array of length `Q_1d` holding the locations of quadrature points on the 1D reference element `[-1, 1]`
956   @param[in]  q_weight_1d Array of length `Q_1d` holding the quadrature weights on the reference element
957   @param[out] basis       Address of the variable where the newly created `CeedBasis` will be stored
958 
959   @return An error code: 0 - success, otherwise - failure
960 
961   @ref User
962 **/
963 int CeedBasisCreateTensorH1(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P_1d, CeedInt Q_1d, const CeedScalar *interp_1d,
964                             const CeedScalar *grad_1d, const CeedScalar *q_ref_1d, const CeedScalar *q_weight_1d, CeedBasis *basis) {
965   if (!ceed->BasisCreateTensorH1) {
966     Ceed delegate;
967 
968     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
969     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not support BasisCreateTensorH1");
970     CeedCall(CeedBasisCreateTensorH1(delegate, dim, num_comp, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
971     return CEED_ERROR_SUCCESS;
972   }
973 
974   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
975   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
976   CeedCheck(P_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
977   CeedCheck(Q_1d > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
978 
979   CeedElemTopology topo = dim == 1 ? CEED_TOPOLOGY_LINE : dim == 2 ? CEED_TOPOLOGY_QUAD : CEED_TOPOLOGY_HEX;
980 
981   CeedCall(CeedCalloc(1, basis));
982   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
983   (*basis)->ref_count       = 1;
984   (*basis)->is_tensor_basis = true;
985   (*basis)->dim             = dim;
986   (*basis)->topo            = topo;
987   (*basis)->num_comp        = num_comp;
988   (*basis)->P_1d            = P_1d;
989   (*basis)->Q_1d            = Q_1d;
990   (*basis)->P               = CeedIntPow(P_1d, dim);
991   (*basis)->Q               = CeedIntPow(Q_1d, dim);
992   (*basis)->fe_space        = CEED_FE_SPACE_H1;
993   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_ref_1d));
994   CeedCall(CeedCalloc(Q_1d, &(*basis)->q_weight_1d));
995   if (q_ref_1d) memcpy((*basis)->q_ref_1d, q_ref_1d, Q_1d * sizeof(q_ref_1d[0]));
996   if (q_weight_1d) memcpy((*basis)->q_weight_1d, q_weight_1d, Q_1d * sizeof(q_weight_1d[0]));
997   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->interp_1d));
998   CeedCall(CeedCalloc(Q_1d * P_1d, &(*basis)->grad_1d));
999   if (interp_1d) memcpy((*basis)->interp_1d, interp_1d, Q_1d * P_1d * sizeof(interp_1d[0]));
1000   if (grad_1d) memcpy((*basis)->grad_1d, grad_1d, Q_1d * P_1d * sizeof(grad_1d[0]));
1001   CeedCall(ceed->BasisCreateTensorH1(dim, P_1d, Q_1d, interp_1d, grad_1d, q_ref_1d, q_weight_1d, *basis));
1002   return CEED_ERROR_SUCCESS;
1003 }
1004 
1005 /**
1006   @brief Create a tensor-product \f$H^1\f$ Lagrange basis
1007 
1008   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1009   @param[in]  dim       Topological dimension of element
1010   @param[in]  num_comp  Number of field components (1 for scalar fields)
1011   @param[in]  P         Number of Gauss-Lobatto nodes in one dimension.
1012                           The polynomial degree of the resulting `Q_k` element is `k = P - 1`.
1013   @param[in]  Q         Number of quadrature points in one dimension.
1014   @param[in]  quad_mode Distribution of the `Q` quadrature points (affects order of accuracy for the quadrature)
1015   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1016 
1017   @return An error code: 0 - success, otherwise - failure
1018 
1019   @ref User
1020 **/
1021 int CeedBasisCreateTensorH1Lagrange(Ceed ceed, CeedInt dim, CeedInt num_comp, CeedInt P, CeedInt Q, CeedQuadMode quad_mode, CeedBasis *basis) {
1022   // Allocate
1023   int        ierr = CEED_ERROR_SUCCESS;
1024   CeedScalar c1, c2, c3, c4, dx, *nodes, *interp_1d, *grad_1d, *q_ref_1d, *q_weight_1d;
1025 
1026   CeedCheck(dim > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis dimension must be a positive value");
1027   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1028   CeedCheck(P > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1029   CeedCheck(Q > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1030 
1031   // Get Nodes and Weights
1032   CeedCall(CeedCalloc(P * Q, &interp_1d));
1033   CeedCall(CeedCalloc(P * Q, &grad_1d));
1034   CeedCall(CeedCalloc(P, &nodes));
1035   CeedCall(CeedCalloc(Q, &q_ref_1d));
1036   CeedCall(CeedCalloc(Q, &q_weight_1d));
1037   if (CeedLobattoQuadrature(P, nodes, NULL) != CEED_ERROR_SUCCESS) goto cleanup;
1038   switch (quad_mode) {
1039     case CEED_GAUSS:
1040       ierr = CeedGaussQuadrature(Q, q_ref_1d, q_weight_1d);
1041       break;
1042     case CEED_GAUSS_LOBATTO:
1043       ierr = CeedLobattoQuadrature(Q, q_ref_1d, q_weight_1d);
1044       break;
1045   }
1046   if (ierr != CEED_ERROR_SUCCESS) goto cleanup;
1047 
1048   // Build B, D matrix
1049   // Fornberg, 1998
1050   for (CeedInt i = 0; i < Q; i++) {
1051     c1                   = 1.0;
1052     c3                   = nodes[0] - q_ref_1d[i];
1053     interp_1d[i * P + 0] = 1.0;
1054     for (CeedInt j = 1; j < P; j++) {
1055       c2 = 1.0;
1056       c4 = c3;
1057       c3 = nodes[j] - q_ref_1d[i];
1058       for (CeedInt k = 0; k < j; k++) {
1059         dx = nodes[j] - nodes[k];
1060         c2 *= dx;
1061         if (k == j - 1) {
1062           grad_1d[i * P + j]   = c1 * (interp_1d[i * P + k] - c4 * grad_1d[i * P + k]) / c2;
1063           interp_1d[i * P + j] = -c1 * c4 * interp_1d[i * P + k] / c2;
1064         }
1065         grad_1d[i * P + k]   = (c3 * grad_1d[i * P + k] - interp_1d[i * P + k]) / dx;
1066         interp_1d[i * P + k] = c3 * interp_1d[i * P + k] / dx;
1067       }
1068       c1 = c2;
1069     }
1070   }
1071   // Pass to CeedBasisCreateTensorH1
1072   CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P, Q, interp_1d, grad_1d, q_ref_1d, q_weight_1d, basis));
1073 cleanup:
1074   CeedCall(CeedFree(&interp_1d));
1075   CeedCall(CeedFree(&grad_1d));
1076   CeedCall(CeedFree(&nodes));
1077   CeedCall(CeedFree(&q_ref_1d));
1078   CeedCall(CeedFree(&q_weight_1d));
1079   return CEED_ERROR_SUCCESS;
1080 }
1081 
1082 /**
1083   @brief Create a non tensor-product basis for \f$H^1\f$ discretizations
1084 
1085   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1086   @param[in]  topo      Topology of element, e.g. hypercube, simplex, ect
1087   @param[in]  num_comp  Number of field components (1 for scalar fields)
1088   @param[in]  num_nodes Total number of nodes
1089   @param[in]  num_qpts  Total number of quadrature points
1090   @param[in]  interp    Row-major (`num_qpts * num_nodes`) matrix expressing the values of nodal basis functions at quadrature points
1091   @param[in]  grad      Row-major (`dim * num_qpts * num_nodes`) matrix expressing derivatives of nodal basis functions at quadrature points
1092   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1093   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1094   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1095 
1096   @return An error code: 0 - success, otherwise - failure
1097 
1098   @ref User
1099 **/
1100 int CeedBasisCreateH1(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1101                       const CeedScalar *grad, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1102   CeedInt P = num_nodes, Q = num_qpts, dim = 0;
1103 
1104   if (!ceed->BasisCreateH1) {
1105     Ceed delegate;
1106 
1107     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1108     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not support BasisCreateH1");
1109     CeedCall(CeedBasisCreateH1(delegate, topo, num_comp, num_nodes, num_qpts, interp, grad, q_ref, q_weight, basis));
1110     return CEED_ERROR_SUCCESS;
1111   }
1112 
1113   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1114   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1115   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1116 
1117   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1118 
1119   CeedCall(CeedCalloc(1, basis));
1120   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1121   (*basis)->ref_count       = 1;
1122   (*basis)->is_tensor_basis = false;
1123   (*basis)->dim             = dim;
1124   (*basis)->topo            = topo;
1125   (*basis)->num_comp        = num_comp;
1126   (*basis)->P               = P;
1127   (*basis)->Q               = Q;
1128   (*basis)->fe_space        = CEED_FE_SPACE_H1;
1129   CeedCall(CeedCalloc(Q * dim, &(*basis)->q_ref_1d));
1130   CeedCall(CeedCalloc(Q, &(*basis)->q_weight_1d));
1131   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1132   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1133   CeedCall(CeedCalloc(Q * P, &(*basis)->interp));
1134   CeedCall(CeedCalloc(dim * Q * P, &(*basis)->grad));
1135   if (interp) memcpy((*basis)->interp, interp, Q * P * sizeof(interp[0]));
1136   if (grad) memcpy((*basis)->grad, grad, dim * Q * P * sizeof(grad[0]));
1137   CeedCall(ceed->BasisCreateH1(topo, dim, P, Q, interp, grad, q_ref, q_weight, *basis));
1138   return CEED_ERROR_SUCCESS;
1139 }
1140 
1141 /**
1142   @brief Create a non tensor-product basis for \f$H(\mathrm{div})\f$ discretizations
1143 
1144   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1145   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1146   @param[in]  num_comp  Number of components (usually 1 for vectors in H(div) bases)
1147   @param[in]  num_nodes Total number of nodes (DoFs per element)
1148   @param[in]  num_qpts  Total number of quadrature points
1149   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1150   @param[in]  div       Row-major (`num_qpts * num_nodes`) matrix expressing divergence of basis functions at quadrature points
1151   @param[in]  q_ref     Array of length `num_qpts` * dim holding the locations of quadrature points on the reference element
1152   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1153   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1154 
1155   @return An error code: 0 - success, otherwise - failure
1156 
1157   @ref User
1158 **/
1159 int CeedBasisCreateHdiv(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1160                         const CeedScalar *div, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1161   CeedInt Q = num_qpts, P = num_nodes, dim = 0;
1162 
1163   if (!ceed->BasisCreateHdiv) {
1164     Ceed delegate;
1165 
1166     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1167     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHdiv");
1168     CeedCall(CeedBasisCreateHdiv(delegate, topo, num_comp, num_nodes, num_qpts, interp, div, q_ref, q_weight, basis));
1169     return CEED_ERROR_SUCCESS;
1170   }
1171 
1172   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1173   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1174   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1175 
1176   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1177 
1178   CeedCall(CeedCalloc(1, basis));
1179   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1180   (*basis)->ref_count       = 1;
1181   (*basis)->is_tensor_basis = false;
1182   (*basis)->dim             = dim;
1183   (*basis)->topo            = topo;
1184   (*basis)->num_comp        = num_comp;
1185   (*basis)->P               = P;
1186   (*basis)->Q               = Q;
1187   (*basis)->fe_space        = CEED_FE_SPACE_HDIV;
1188   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1189   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1190   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1191   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1192   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1193   CeedCall(CeedMalloc(Q * P, &(*basis)->div));
1194   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1195   if (div) memcpy((*basis)->div, div, Q * P * sizeof(div[0]));
1196   CeedCall(ceed->BasisCreateHdiv(topo, dim, P, Q, interp, div, q_ref, q_weight, *basis));
1197   return CEED_ERROR_SUCCESS;
1198 }
1199 
1200 /**
1201   @brief Create a non tensor-product basis for \f$H(\mathrm{curl})\f$ discretizations
1202 
1203   @param[in]  ceed      `Ceed` object used to create the `CeedBasis`
1204   @param[in]  topo      Topology of element (`CEED_TOPOLOGY_QUAD`, `CEED_TOPOLOGY_PRISM`, etc.), dimension of which is used in some array sizes below
1205   @param[in]  num_comp  Number of components (usually 1 for vectors in \f$H(\mathrm{curl})\f$ bases)
1206   @param[in]  num_nodes Total number of nodes (DoFs per element)
1207   @param[in]  num_qpts  Total number of quadrature points
1208   @param[in]  interp    Row-major (`dim * num_qpts * num_nodes`) matrix expressing the values of basis functions at quadrature points
1209   @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
1210   @param[in]  q_ref     Array of length `num_qpts * dim` holding the locations of quadrature points on the reference element
1211   @param[in]  q_weight  Array of length `num_qpts` holding the quadrature weights on the reference element
1212   @param[out] basis     Address of the variable where the newly created `CeedBasis` will be stored
1213 
1214   @return An error code: 0 - success, otherwise - failure
1215 
1216   @ref User
1217 **/
1218 int CeedBasisCreateHcurl(Ceed ceed, CeedElemTopology topo, CeedInt num_comp, CeedInt num_nodes, CeedInt num_qpts, const CeedScalar *interp,
1219                          const CeedScalar *curl, const CeedScalar *q_ref, const CeedScalar *q_weight, CeedBasis *basis) {
1220   CeedInt Q = num_qpts, P = num_nodes, dim = 0, curl_comp = 0;
1221 
1222   if (!ceed->BasisCreateHcurl) {
1223     Ceed delegate;
1224 
1225     CeedCall(CeedGetObjectDelegate(ceed, &delegate, "Basis"));
1226     CeedCheck(delegate, ceed, CEED_ERROR_UNSUPPORTED, "Backend does not implement BasisCreateHcurl");
1227     CeedCall(CeedBasisCreateHcurl(delegate, topo, num_comp, num_nodes, num_qpts, interp, curl, q_ref, q_weight, basis));
1228     return CEED_ERROR_SUCCESS;
1229   }
1230 
1231   CeedCheck(num_comp > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 component");
1232   CeedCheck(num_nodes > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 node");
1233   CeedCheck(num_qpts > 0, ceed, CEED_ERROR_DIMENSION, "CeedBasis must have at least 1 quadrature point");
1234 
1235   CeedCall(CeedBasisGetTopologyDimension(topo, &dim));
1236   curl_comp = (dim < 3) ? 1 : dim;
1237 
1238   CeedCall(CeedCalloc(1, basis));
1239   CeedCall(CeedReferenceCopy(ceed, &(*basis)->ceed));
1240   (*basis)->ref_count       = 1;
1241   (*basis)->is_tensor_basis = false;
1242   (*basis)->dim             = dim;
1243   (*basis)->topo            = topo;
1244   (*basis)->num_comp        = num_comp;
1245   (*basis)->P               = P;
1246   (*basis)->Q               = Q;
1247   (*basis)->fe_space        = CEED_FE_SPACE_HCURL;
1248   CeedCall(CeedMalloc(Q * dim, &(*basis)->q_ref_1d));
1249   CeedCall(CeedMalloc(Q, &(*basis)->q_weight_1d));
1250   if (q_ref) memcpy((*basis)->q_ref_1d, q_ref, Q * dim * sizeof(q_ref[0]));
1251   if (q_weight) memcpy((*basis)->q_weight_1d, q_weight, Q * sizeof(q_weight[0]));
1252   CeedCall(CeedMalloc(dim * Q * P, &(*basis)->interp));
1253   CeedCall(CeedMalloc(curl_comp * Q * P, &(*basis)->curl));
1254   if (interp) memcpy((*basis)->interp, interp, dim * Q * P * sizeof(interp[0]));
1255   if (curl) memcpy((*basis)->curl, curl, curl_comp * Q * P * sizeof(curl[0]));
1256   CeedCall(ceed->BasisCreateHcurl(topo, dim, P, Q, interp, curl, q_ref, q_weight, *basis));
1257   return CEED_ERROR_SUCCESS;
1258 }
1259 
1260 /**
1261   @brief Create a `CeedBasis` for projection from the nodes of `basis_from` to the nodes of `basis_to`.
1262 
1263   Only @ref CEED_EVAL_INTERP will be valid for the new basis, `basis_project`.
1264   For \f$H^1\f$ spaces, @ref CEED_EVAL_GRAD will also be valid.
1265   The interpolation is given by `interp_project = interp_to^+ * interp_from`, where the pseudoinverse `interp_to^+` is given by QR factorization.
1266   The gradient (for the \f$H^1\f$ case) is given by `grad_project = interp_to^+ * grad_from`.
1267 
1268   Note: `basis_from` and `basis_to` must have compatible quadrature spaces.
1269 
1270   Note: `basis_project` will have the same number of components as `basis_from`, regardless of the number of components that `basis_to` has.
1271         If `basis_from` has 3 components and `basis_to` has 5 components, then `basis_project` will have 3 components.
1272 
1273   @param[in]  basis_from    `CeedBasis` to prolong from
1274   @param[in]  basis_to      `CeedBasis` to prolong to
1275   @param[out] basis_project Address of the variable where the newly created `CeedBasis` will be stored
1276 
1277   @return An error code: 0 - success, otherwise - failure
1278 
1279   @ref User
1280 **/
1281 int CeedBasisCreateProjection(CeedBasis basis_from, CeedBasis basis_to, CeedBasis *basis_project) {
1282   Ceed        ceed;
1283   bool        is_tensor;
1284   CeedInt     dim, num_comp;
1285   CeedScalar *q_ref, *q_weight, *interp_project, *grad_project;
1286 
1287   CeedCall(CeedBasisGetCeed(basis_to, &ceed));
1288 
1289   // Create projection matrix
1290   CeedCall(CeedBasisCreateProjectionMatrices(basis_from, basis_to, &interp_project, &grad_project));
1291 
1292   // Build basis
1293   CeedCall(CeedBasisIsTensor(basis_to, &is_tensor));
1294   CeedCall(CeedBasisGetDimension(basis_to, &dim));
1295   CeedCall(CeedBasisGetNumComponents(basis_from, &num_comp));
1296   if (is_tensor) {
1297     CeedInt P_1d_to, P_1d_from;
1298 
1299     CeedCall(CeedBasisGetNumNodes1D(basis_from, &P_1d_from));
1300     CeedCall(CeedBasisGetNumNodes1D(basis_to, &P_1d_to));
1301     CeedCall(CeedCalloc(P_1d_to, &q_ref));
1302     CeedCall(CeedCalloc(P_1d_to, &q_weight));
1303     CeedCall(CeedBasisCreateTensorH1(ceed, dim, num_comp, P_1d_from, P_1d_to, interp_project, grad_project, q_ref, q_weight, basis_project));
1304   } else {
1305     // Even if basis_to and basis_from are not H1, the resulting basis is H1 for interpolation to work
1306     CeedInt          num_nodes_to, num_nodes_from;
1307     CeedElemTopology topo;
1308 
1309     CeedCall(CeedBasisGetTopology(basis_to, &topo));
1310     CeedCall(CeedBasisGetNumNodes(basis_from, &num_nodes_from));
1311     CeedCall(CeedBasisGetNumNodes(basis_to, &num_nodes_to));
1312     CeedCall(CeedCalloc(num_nodes_to * dim, &q_ref));
1313     CeedCall(CeedCalloc(num_nodes_to, &q_weight));
1314     CeedCall(CeedBasisCreateH1(ceed, topo, num_comp, num_nodes_from, num_nodes_to, interp_project, grad_project, q_ref, q_weight, basis_project));
1315   }
1316 
1317   // Cleanup
1318   CeedCall(CeedFree(&interp_project));
1319   CeedCall(CeedFree(&grad_project));
1320   CeedCall(CeedFree(&q_ref));
1321   CeedCall(CeedFree(&q_weight));
1322   return CEED_ERROR_SUCCESS;
1323 }
1324 
1325 /**
1326   @brief Copy the pointer to a `CeedBasis`.
1327 
1328   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`.
1329         This `CeedBasis` will be destroyed if `*basis_copy` is the only reference to this `CeedBasis`.
1330 
1331   @param[in]     basis      `CeedBasis` to copy reference to
1332   @param[in,out] basis_copy Variable to store copied reference
1333 
1334   @return An error code: 0 - success, otherwise - failure
1335 
1336   @ref User
1337 **/
1338 int CeedBasisReferenceCopy(CeedBasis basis, CeedBasis *basis_copy) {
1339   if (basis != CEED_BASIS_NONE) CeedCall(CeedBasisReference(basis));
1340   CeedCall(CeedBasisDestroy(basis_copy));
1341   *basis_copy = basis;
1342   return CEED_ERROR_SUCCESS;
1343 }
1344 
1345 /**
1346   @brief View a `CeedBasis`
1347 
1348   @param[in] basis  `CeedBasis` to view
1349   @param[in] stream Stream to view to, e.g., `stdout`
1350 
1351   @return An error code: 0 - success, otherwise - failure
1352 
1353   @ref User
1354 **/
1355 int CeedBasisView(CeedBasis basis, FILE *stream) {
1356   CeedInt          q_comp   = 0;
1357   CeedElemTopology topo     = basis->topo;
1358   CeedFESpace      fe_space = basis->fe_space;
1359 
1360   // Print FE space and element topology of the basis
1361   fprintf(stream, "CeedBasis in a %s on a %s element\n", CeedFESpaces[fe_space], CeedElemTopologies[topo]);
1362   if (basis->is_tensor_basis) {
1363     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P_1d, basis->Q_1d);
1364   } else {
1365     fprintf(stream, "  P: %" CeedInt_FMT "\n  Q: %" CeedInt_FMT "\n", basis->P, basis->Q);
1366   }
1367   fprintf(stream, "  dimension: %" CeedInt_FMT "\n  field components: %" CeedInt_FMT "\n", basis->dim, basis->num_comp);
1368   // Print quadrature data, interpolation/gradient/divergence/curl of the basis
1369   if (basis->is_tensor_basis) {  // tensor basis
1370     CeedCall(CeedScalarView("qref1d", "\t% 12.8f", 1, basis->Q_1d, basis->q_ref_1d, stream));
1371     CeedCall(CeedScalarView("qweight1d", "\t% 12.8f", 1, basis->Q_1d, basis->q_weight_1d, stream));
1372     CeedCall(CeedScalarView("interp1d", "\t% 12.8f", basis->Q_1d, basis->P_1d, basis->interp_1d, stream));
1373     CeedCall(CeedScalarView("grad1d", "\t% 12.8f", basis->Q_1d, basis->P_1d, basis->grad_1d, stream));
1374   } else {  // non-tensor basis
1375     CeedCall(CeedScalarView("qref", "\t% 12.8f", 1, basis->Q * basis->dim, basis->q_ref_1d, stream));
1376     CeedCall(CeedScalarView("qweight", "\t% 12.8f", 1, basis->Q, basis->q_weight_1d, stream));
1377     CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_INTERP, &q_comp));
1378     CeedCall(CeedScalarView("interp", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->interp, stream));
1379     if (basis->grad) {
1380       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_GRAD, &q_comp));
1381       CeedCall(CeedScalarView("grad", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->grad, stream));
1382     }
1383     if (basis->div) {
1384       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_DIV, &q_comp));
1385       CeedCall(CeedScalarView("div", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->div, stream));
1386     }
1387     if (basis->curl) {
1388       CeedCall(CeedBasisGetNumQuadratureComponents(basis, CEED_EVAL_CURL, &q_comp));
1389       CeedCall(CeedScalarView("curl", "\t% 12.8f", q_comp * basis->Q, basis->P, basis->curl, stream));
1390     }
1391   }
1392   return CEED_ERROR_SUCCESS;
1393 }
1394 
1395 /**
1396   @brief Apply basis evaluation from nodes to quadrature points or vice versa
1397 
1398   @param[in]  basis     `CeedBasis` to evaluate
1399   @param[in]  num_elem  The number of elements to apply the basis evaluation to;
1400                           the backend will specify the ordering in @ref CeedElemRestrictionCreate()
1401   @param[in]  t_mode    @ref CEED_NOTRANSPOSE to evaluate from nodes to quadrature points;
1402                           @ref CEED_TRANSPOSE to apply the transpose, mapping from quadrature points to nodes
1403   @param[in]  eval_mode @ref CEED_EVAL_NONE to use values directly,
1404                           @ref CEED_EVAL_INTERP to use interpolated values,
1405                           @ref CEED_EVAL_GRAD to use gradients,
1406                           @ref CEED_EVAL_DIV to use divergence,
1407                           @ref CEED_EVAL_CURL to use curl,
1408                           @ref CEED_EVAL_WEIGHT to use quadrature weights
1409   @param[in]  u         Input `CeedVector`
1410   @param[out] v         Output `CeedVector`
1411 
1412   @return An error code: 0 - success, otherwise - failure
1413 
1414   @ref User
1415 **/
1416 int CeedBasisApply(CeedBasis basis, CeedInt num_elem, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector u, CeedVector v) {
1417   CeedInt  dim, num_comp, q_comp, num_nodes, num_qpts;
1418   CeedSize u_length = 0, v_length;
1419 
1420   CeedCall(CeedBasisGetDimension(basis, &dim));
1421   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1422   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &q_comp));
1423   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1424   CeedCall(CeedBasisGetNumQuadraturePoints(basis, &num_qpts));
1425   CeedCall(CeedVectorGetLength(v, &v_length));
1426   if (u) CeedCall(CeedVectorGetLength(u, &u_length));
1427 
1428   CeedCheck(basis->Apply, basis->ceed, CEED_ERROR_UNSUPPORTED, "Backend does not support CeedBasisApply");
1429 
1430   // Check compatibility of topological and geometrical dimensions
1431   CeedCheck((t_mode == CEED_TRANSPOSE && v_length % num_nodes == 0 && u_length % num_qpts == 0) ||
1432                 (t_mode == CEED_NOTRANSPOSE && u_length % num_nodes == 0 && v_length % num_qpts == 0),
1433             basis->ceed, CEED_ERROR_DIMENSION, "Length of input/output vectors incompatible with basis dimensions");
1434 
1435   // Check vector lengths to prevent out of bounds issues
1436   bool good_dims = true;
1437   switch (eval_mode) {
1438     case CEED_EVAL_NONE:
1439     case CEED_EVAL_INTERP:
1440     case CEED_EVAL_GRAD:
1441     case CEED_EVAL_DIV:
1442     case CEED_EVAL_CURL:
1443       good_dims =
1444           ((t_mode == CEED_TRANSPOSE && u_length >= num_elem * num_comp * num_qpts * q_comp && v_length >= num_elem * num_comp * num_nodes) ||
1445            (t_mode == CEED_NOTRANSPOSE && v_length >= num_elem * num_qpts * num_comp * q_comp && u_length >= num_elem * num_comp * num_nodes));
1446       break;
1447     case CEED_EVAL_WEIGHT:
1448       good_dims = v_length >= num_elem * num_qpts;
1449       break;
1450   }
1451   CeedCheck(good_dims, basis->ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
1452 
1453   CeedCall(basis->Apply(basis, num_elem, t_mode, eval_mode, u, v));
1454   return CEED_ERROR_SUCCESS;
1455 }
1456 
1457 /**
1458   @brief Apply basis evaluation from nodes to arbitrary points
1459 
1460   @param[in]  basis      `CeedBasis` to evaluate
1461   @param[in]  num_points The number of points to apply the basis evaluation to
1462   @param[in]  t_mode     @ref CEED_NOTRANSPOSE to evaluate from nodes to points;
1463                            @ref CEED_TRANSPOSE to apply the transpose, mapping from points to nodes
1464   @param[in]  eval_mode  @ref CEED_EVAL_INTERP to use interpolated values,
1465                            @ref CEED_EVAL_GRAD to use gradients,
1466                            @ref CEED_EVAL_WEIGHT to use quadrature weights
1467   @param[in]  x_ref      `CeedVector` holding reference coordinates of each point
1468   @param[in]  u          Input `CeedVector`, of length `num_nodes * num_comp` for @ref CEED_NOTRANSPOSE
1469   @param[out] v          Output `CeedVector`, of length `num_points * num_q_comp` for @ref CEED_NOTRANSPOSE with @ref CEED_EVAL_INTERP
1470 
1471   @return An error code: 0 - success, otherwise - failure
1472 
1473   @ref User
1474 **/
1475 int CeedBasisApplyAtPoints(CeedBasis basis, CeedInt num_points, CeedTransposeMode t_mode, CeedEvalMode eval_mode, CeedVector x_ref, CeedVector u,
1476                            CeedVector v) {
1477   CeedInt  dim, num_comp, num_q_comp, num_nodes, P_1d = 1, Q_1d = 1;
1478   CeedSize x_length = 0, u_length = 0, v_length;
1479 
1480   CeedCall(CeedBasisGetDimension(basis, &dim));
1481   CeedCall(CeedBasisGetNumNodes1D(basis, &P_1d));
1482   CeedCall(CeedBasisGetNumQuadraturePoints1D(basis, &Q_1d));
1483   CeedCall(CeedBasisGetNumComponents(basis, &num_comp));
1484   CeedCall(CeedBasisGetNumQuadratureComponents(basis, eval_mode, &num_q_comp));
1485   CeedCall(CeedBasisGetNumNodes(basis, &num_nodes));
1486   CeedCall(CeedVectorGetLength(v, &v_length));
1487   if (x_ref != CEED_VECTOR_NONE) CeedCall(CeedVectorGetLength(x_ref, &x_length));
1488   if (u != CEED_VECTOR_NONE) CeedCall(CeedVectorGetLength(u, &u_length));
1489 
1490   // Check compatibility of topological and geometrical dimensions
1491   CeedCheck((t_mode == CEED_TRANSPOSE && v_length % num_nodes == 0) || (t_mode == CEED_NOTRANSPOSE && u_length % num_nodes == 0) ||
1492                 (eval_mode == CEED_EVAL_WEIGHT),
1493             basis->ceed, CEED_ERROR_DIMENSION, "Length of input/output vectors incompatible with basis dimensions and number of points");
1494 
1495   // Check compatibility coordinates vector
1496   CeedCheck((x_length >= num_points * dim) || (eval_mode == CEED_EVAL_WEIGHT), basis->ceed, CEED_ERROR_DIMENSION,
1497             "Length of reference coordinate vector incompatible with basis dimension and number of points");
1498 
1499   // Check CEED_EVAL_WEIGHT only on CEED_NOTRANSPOSE
1500   CeedCheck(eval_mode != CEED_EVAL_WEIGHT || t_mode == CEED_NOTRANSPOSE, basis->ceed, CEED_ERROR_UNSUPPORTED,
1501             "CEED_EVAL_WEIGHT only supported with CEED_NOTRANSPOSE");
1502 
1503   // Check vector lengths to prevent out of bounds issues
1504   bool good_dims = false;
1505   switch (eval_mode) {
1506     case CEED_EVAL_INTERP:
1507       good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= num_points * num_q_comp || v_length >= num_nodes * num_comp)) ||
1508                    (t_mode == CEED_NOTRANSPOSE && (v_length >= num_points * num_q_comp || u_length >= num_nodes * num_comp)));
1509       break;
1510     case CEED_EVAL_GRAD:
1511       good_dims = ((t_mode == CEED_TRANSPOSE && (u_length >= num_points * num_q_comp * dim || v_length >= num_nodes * num_comp)) ||
1512                    (t_mode == CEED_NOTRANSPOSE && (v_length >= num_points * num_q_comp * dim || u_length >= num_nodes * num_comp)));
1513       break;
1514     case CEED_EVAL_WEIGHT:
1515       good_dims = t_mode == CEED_NOTRANSPOSE && (v_length >= num_points);
1516       break;
1517     case CEED_EVAL_NONE:
1518     case CEED_EVAL_DIV:
1519     case CEED_EVAL_CURL:
1520       // LCOV_EXCL_START
1521       return CeedError(basis->ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points not supported for %s", CeedEvalModes[eval_mode]);
1522       // LCOV_EXCL_STOP
1523   }
1524   CeedCheck(good_dims, basis->ceed, CEED_ERROR_DIMENSION, "Input/output vectors too short for basis and evaluation mode");
1525 
1526   // Backend method
1527   if (basis->ApplyAtPoints) {
1528     CeedCall(basis->ApplyAtPoints(basis, num_points, t_mode, eval_mode, x_ref, u, v));
1529     return CEED_ERROR_SUCCESS;
1530   }
1531 
1532   // Default implementation
1533   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_UNSUPPORTED, "Evaluation at arbitrary points only supported for tensor product bases");
1534   if (eval_mode == CEED_EVAL_WEIGHT) {
1535     CeedCall(CeedVectorSetValue(v, 1.0));
1536     return CEED_ERROR_SUCCESS;
1537   }
1538   if (!basis->basis_chebyshev) {
1539     // Build matrix mapping from quadrature point values to Chebyshev coefficients
1540     CeedScalar       *C, *chebyshev_coeffs_1d_inv;
1541     const CeedScalar *q_ref_1d;
1542 
1543     // Build coefficient matrix
1544     // -- Note: Clang-tidy needs this check because it does not understand the is_tensor_basis check above
1545     CeedCheck(P_1d > 0 && Q_1d > 0, basis->ceed, CEED_ERROR_INCOMPATIBLE, "CeedBasis dimensions are malformed");
1546     CeedCall(CeedCalloc(Q_1d * Q_1d, &C));
1547     CeedCall(CeedBasisGetQRef(basis, &q_ref_1d));
1548     for (CeedInt i = 0; i < Q_1d; i++) CeedCall(CeedChebyshevPolynomialsAtPoint(q_ref_1d[i], Q_1d, &C[i * Q_1d]));
1549 
1550     // Compute C^+, pseudoinverse of coefficient matrix
1551     CeedCall(CeedCalloc(Q_1d * Q_1d, &chebyshev_coeffs_1d_inv));
1552     CeedCall(CeedMatrixPseudoinverse(basis->ceed, C, Q_1d, Q_1d, chebyshev_coeffs_1d_inv));
1553 
1554     // Build basis mapping from nodes to Chebyshev coefficients
1555     CeedScalar       *chebyshev_interp_1d, *chebyshev_grad_1d, *chebyshev_q_weight_1d;
1556     const CeedScalar *interp_1d;
1557 
1558     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_interp_1d));
1559     CeedCall(CeedCalloc(P_1d * Q_1d, &chebyshev_grad_1d));
1560     CeedCall(CeedCalloc(Q_1d, &chebyshev_q_weight_1d));
1561     CeedCall(CeedBasisGetInterp1D(basis, &interp_1d));
1562     CeedCall(CeedMatrixMatrixMultiply(basis->ceed, chebyshev_coeffs_1d_inv, interp_1d, chebyshev_interp_1d, Q_1d, P_1d, Q_1d));
1563 
1564     CeedCall(CeedVectorCreate(basis->ceed, num_comp * CeedIntPow(Q_1d, dim), &basis->vec_chebyshev));
1565     CeedCall(CeedBasisCreateTensorH1(basis->ceed, dim, num_comp, P_1d, Q_1d, chebyshev_interp_1d, chebyshev_grad_1d, q_ref_1d, chebyshev_q_weight_1d,
1566                                      &basis->basis_chebyshev));
1567 
1568     // Cleanup
1569     CeedCall(CeedFree(&C));
1570     CeedCall(CeedFree(&chebyshev_coeffs_1d_inv));
1571     CeedCall(CeedFree(&chebyshev_interp_1d));
1572     CeedCall(CeedFree(&chebyshev_grad_1d));
1573     CeedCall(CeedFree(&chebyshev_q_weight_1d));
1574   }
1575 
1576   // Create TensorContract object if needed, such as a basis from the GPU backends
1577   if (!basis->contract) {
1578     Ceed      ceed_ref;
1579     CeedBasis basis_ref = NULL;
1580 
1581     CeedCall(CeedInit("/cpu/self", &ceed_ref));
1582     // Only need matching tensor contraction dimensions, any type of basis will work
1583     CeedCall(CeedBasisCreateTensorH1Lagrange(ceed_ref, dim, num_comp, P_1d, Q_1d, CEED_GAUSS, &basis_ref));
1584     // Note - clang-tidy doesn't know basis_ref->contract must be valid here
1585     CeedCheck(basis_ref && basis_ref->contract, basis->ceed, CEED_ERROR_UNSUPPORTED,
1586               "Reference CPU ceed failed to create a tensor contraction object");
1587     CeedCall(CeedTensorContractReferenceCopy(basis_ref->contract, &basis->contract));
1588     CeedCall(CeedBasisDestroy(&basis_ref));
1589     CeedCall(CeedDestroy(&ceed_ref));
1590   }
1591 
1592   // Basis evaluation
1593   switch (t_mode) {
1594     case CEED_NOTRANSPOSE: {
1595       // Nodes to arbitrary points
1596       CeedScalar       *v_array;
1597       const CeedScalar *chebyshev_coeffs, *x_array_read;
1598 
1599       // -- Interpolate to Chebyshev coefficients
1600       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_NOTRANSPOSE, CEED_EVAL_INTERP, u, basis->vec_chebyshev));
1601 
1602       // -- Evaluate Chebyshev polynomials at arbitrary points
1603       CeedCall(CeedVectorGetArrayRead(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
1604       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
1605       CeedCall(CeedVectorGetArrayWrite(v, CEED_MEM_HOST, &v_array));
1606       switch (eval_mode) {
1607         case CEED_EVAL_INTERP: {
1608           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
1609 
1610           // ---- Values at point
1611           for (CeedInt p = 0; p < num_points; p++) {
1612             CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
1613 
1614             for (CeedInt d = 0; d < dim; d++) {
1615               // ------ Tensor contract with current Chebyshev polynomial values
1616               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * num_points + p], Q_1d, chebyshev_x));
1617               CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
1618                                                d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
1619               pre /= Q_1d;
1620               post *= 1;
1621             }
1622             for (CeedInt c = 0; c < num_comp; c++) v_array[c * num_points + p] = tmp[dim % 2][c];
1623           }
1624           break;
1625         }
1626         case CEED_EVAL_GRAD: {
1627           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
1628 
1629           // ---- Values at point
1630           for (CeedInt p = 0; p < num_points; p++) {
1631             // Dim**2 contractions, apply grad when pass == dim
1632             for (CeedInt pass = 0; pass < dim; pass++) {
1633               CeedInt pre = num_comp * CeedIntPow(Q_1d, dim - 1), post = 1;
1634 
1635               for (CeedInt d = 0; d < dim; d++) {
1636                 // ------ Tensor contract with current Chebyshev polynomial values
1637                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * num_points + p], Q_1d, chebyshev_x));
1638                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * num_points + p], Q_1d, chebyshev_x));
1639                 CeedCall(CeedTensorContractApply(basis->contract, pre, Q_1d, post, 1, chebyshev_x, t_mode, false,
1640                                                  d == 0 ? chebyshev_coeffs : tmp[d % 2], tmp[(d + 1) % 2]));
1641                 pre /= Q_1d;
1642                 post *= 1;
1643               }
1644               for (CeedInt c = 0; c < num_comp; c++) v_array[(pass * num_comp + c) * num_points + p] = tmp[dim % 2][c];
1645             }
1646           }
1647           break;
1648         }
1649         default:
1650           // Nothing to do, excluded above
1651           break;
1652       }
1653       CeedCall(CeedVectorRestoreArrayRead(basis->vec_chebyshev, &chebyshev_coeffs));
1654       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
1655       CeedCall(CeedVectorRestoreArray(v, &v_array));
1656       break;
1657     }
1658     case CEED_TRANSPOSE: {
1659       // Note: No switch on e_mode here because only CEED_EVAL_INTERP is supported at this time
1660       // Arbitrary points to nodes
1661       CeedScalar       *chebyshev_coeffs;
1662       const CeedScalar *u_array, *x_array_read;
1663 
1664       // -- Transpose of evaluation of Chebyshev polynomials at arbitrary points
1665       CeedCall(CeedVectorGetArrayWrite(basis->vec_chebyshev, CEED_MEM_HOST, &chebyshev_coeffs));
1666       CeedCall(CeedVectorGetArrayRead(x_ref, CEED_MEM_HOST, &x_array_read));
1667       CeedCall(CeedVectorGetArrayRead(u, CEED_MEM_HOST, &u_array));
1668 
1669       switch (eval_mode) {
1670         case CEED_EVAL_INTERP: {
1671           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
1672 
1673           // ---- Values at point
1674           for (CeedInt p = 0; p < num_points; p++) {
1675             CeedInt pre = num_comp * 1, post = 1;
1676 
1677             for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[c * num_points + p];
1678             for (CeedInt d = 0; d < dim; d++) {
1679               // ------ Tensor contract with current Chebyshev polynomial values
1680               CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * num_points + p], Q_1d, chebyshev_x));
1681               CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode, p > 0 && d == (dim - 1), tmp[d % 2],
1682                                                d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
1683               pre /= 1;
1684               post *= Q_1d;
1685             }
1686           }
1687           break;
1688         }
1689         case CEED_EVAL_GRAD: {
1690           CeedScalar tmp[2][num_comp * CeedIntPow(Q_1d, dim)], chebyshev_x[Q_1d];
1691 
1692           // ---- Values at point
1693           for (CeedInt p = 0; p < num_points; p++) {
1694             // Dim**2 contractions, apply grad when pass == dim
1695             for (CeedInt pass = 0; pass < dim; pass++) {
1696               CeedInt pre = num_comp * 1, post = 1;
1697 
1698               for (CeedInt c = 0; c < num_comp; c++) tmp[0][c] = u_array[(pass * num_comp + c) * num_points + p];
1699               for (CeedInt d = 0; d < dim; d++) {
1700                 // ------ Tensor contract with current Chebyshev polynomial values
1701                 if (pass == d) CeedCall(CeedChebyshevDerivativeAtPoint(x_array_read[d * num_points + p], Q_1d, chebyshev_x));
1702                 else CeedCall(CeedChebyshevPolynomialsAtPoint(x_array_read[d * num_points + p], Q_1d, chebyshev_x));
1703                 CeedCall(CeedTensorContractApply(basis->contract, pre, 1, post, Q_1d, chebyshev_x, t_mode,
1704                                                  (p > 0 || (p == 0 && pass > 0)) && d == (dim - 1), tmp[d % 2],
1705                                                  d == (dim - 1) ? chebyshev_coeffs : tmp[(d + 1) % 2]));
1706                 pre /= 1;
1707                 post *= Q_1d;
1708               }
1709             }
1710           }
1711           break;
1712         }
1713         default:
1714           // Nothing to do, excluded above
1715           break;
1716       }
1717       CeedCall(CeedVectorRestoreArray(basis->vec_chebyshev, &chebyshev_coeffs));
1718       CeedCall(CeedVectorRestoreArrayRead(x_ref, &x_array_read));
1719       CeedCall(CeedVectorRestoreArrayRead(u, &u_array));
1720 
1721       // -- Interpolate transpose from Chebyshev coefficients
1722       CeedCall(CeedBasisApply(basis->basis_chebyshev, 1, CEED_TRANSPOSE, CEED_EVAL_INTERP, basis->vec_chebyshev, v));
1723       break;
1724     }
1725   }
1726   return CEED_ERROR_SUCCESS;
1727 }
1728 
1729 /**
1730   @brief Get `Ceed` associated with a `CeedBasis`
1731 
1732   @param[in]  basis `CeedBasis`
1733   @param[out] ceed  Variable to store `Ceed`
1734 
1735   @return An error code: 0 - success, otherwise - failure
1736 
1737   @ref Advanced
1738 **/
1739 int CeedBasisGetCeed(CeedBasis basis, Ceed *ceed) {
1740   *ceed = basis->ceed;
1741   return CEED_ERROR_SUCCESS;
1742 }
1743 
1744 /**
1745   @brief Get dimension for given `CeedBasis`
1746 
1747   @param[in]  basis `CeedBasis`
1748   @param[out] dim   Variable to store dimension of basis
1749 
1750   @return An error code: 0 - success, otherwise - failure
1751 
1752   @ref Advanced
1753 **/
1754 int CeedBasisGetDimension(CeedBasis basis, CeedInt *dim) {
1755   *dim = basis->dim;
1756   return CEED_ERROR_SUCCESS;
1757 }
1758 
1759 /**
1760   @brief Get topology for given `CeedBasis`
1761 
1762   @param[in]  basis `CeedBasis`
1763   @param[out] topo  Variable to store topology of basis
1764 
1765   @return An error code: 0 - success, otherwise - failure
1766 
1767   @ref Advanced
1768 **/
1769 int CeedBasisGetTopology(CeedBasis basis, CeedElemTopology *topo) {
1770   *topo = basis->topo;
1771   return CEED_ERROR_SUCCESS;
1772 }
1773 
1774 /**
1775   @brief Get number of components for given `CeedBasis`
1776 
1777   @param[in]  basis    `CeedBasis`
1778   @param[out] num_comp Variable to store number of components
1779 
1780   @return An error code: 0 - success, otherwise - failure
1781 
1782   @ref Advanced
1783 **/
1784 int CeedBasisGetNumComponents(CeedBasis basis, CeedInt *num_comp) {
1785   *num_comp = basis->num_comp;
1786   return CEED_ERROR_SUCCESS;
1787 }
1788 
1789 /**
1790   @brief Get total number of nodes (in `dim` dimensions) of a `CeedBasis`
1791 
1792   @param[in]  basis `CeedBasis`
1793   @param[out] P     Variable to store number of nodes
1794 
1795   @return An error code: 0 - success, otherwise - failure
1796 
1797   @ref Utility
1798 **/
1799 int CeedBasisGetNumNodes(CeedBasis basis, CeedInt *P) {
1800   *P = basis->P;
1801   return CEED_ERROR_SUCCESS;
1802 }
1803 
1804 /**
1805   @brief Get total number of nodes (in 1 dimension) of a `CeedBasis`
1806 
1807   @param[in]  basis `CeedBasis`
1808   @param[out] P_1d  Variable to store number of nodes
1809 
1810   @return An error code: 0 - success, otherwise - failure
1811 
1812   @ref Advanced
1813 **/
1814 int CeedBasisGetNumNodes1D(CeedBasis basis, CeedInt *P_1d) {
1815   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "Cannot supply P_1d for non-tensor CeedBasis");
1816   *P_1d = basis->P_1d;
1817   return CEED_ERROR_SUCCESS;
1818 }
1819 
1820 /**
1821   @brief Get total number of quadrature points (in `dim` dimensions) of a `CeedBasis`
1822 
1823   @param[in]  basis `CeedBasis`
1824   @param[out] Q     Variable to store number of quadrature points
1825 
1826   @return An error code: 0 - success, otherwise - failure
1827 
1828   @ref Utility
1829 **/
1830 int CeedBasisGetNumQuadraturePoints(CeedBasis basis, CeedInt *Q) {
1831   *Q = basis->Q;
1832   return CEED_ERROR_SUCCESS;
1833 }
1834 
1835 /**
1836   @brief Get total number of quadrature points (in 1 dimension) of a `CeedBasis`
1837 
1838   @param[in]  basis `CeedBasis`
1839   @param[out] Q_1d  Variable to store number of quadrature points
1840 
1841   @return An error code: 0 - success, otherwise - failure
1842 
1843   @ref Advanced
1844 **/
1845 int CeedBasisGetNumQuadraturePoints1D(CeedBasis basis, CeedInt *Q_1d) {
1846   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "Cannot supply Q_1d for non-tensor CeedBasis");
1847   *Q_1d = basis->Q_1d;
1848   return CEED_ERROR_SUCCESS;
1849 }
1850 
1851 /**
1852   @brief Get reference coordinates of quadrature points (in `dim` dimensions) of a `CeedBasis`
1853 
1854   @param[in]  basis `CeedBasis`
1855   @param[out] q_ref Variable to store reference coordinates of quadrature points
1856 
1857   @return An error code: 0 - success, otherwise - failure
1858 
1859   @ref Advanced
1860 **/
1861 int CeedBasisGetQRef(CeedBasis basis, const CeedScalar **q_ref) {
1862   *q_ref = basis->q_ref_1d;
1863   return CEED_ERROR_SUCCESS;
1864 }
1865 
1866 /**
1867   @brief Get quadrature weights of quadrature points (in `dim` dimensions) of a `CeedBasis`
1868 
1869   @param[in]  basis    `CeedBasis`
1870   @param[out] q_weight Variable to store quadrature weights
1871 
1872   @return An error code: 0 - success, otherwise - failure
1873 
1874   @ref Advanced
1875 **/
1876 int CeedBasisGetQWeights(CeedBasis basis, const CeedScalar **q_weight) {
1877   *q_weight = basis->q_weight_1d;
1878   return CEED_ERROR_SUCCESS;
1879 }
1880 
1881 /**
1882   @brief Get interpolation matrix of a `CeedBasis`
1883 
1884   @param[in]  basis  `CeedBasis`
1885   @param[out] interp Variable to store interpolation matrix
1886 
1887   @return An error code: 0 - success, otherwise - failure
1888 
1889   @ref Advanced
1890 **/
1891 int CeedBasisGetInterp(CeedBasis basis, const CeedScalar **interp) {
1892   if (!basis->interp && basis->is_tensor_basis) {
1893     // Allocate
1894     CeedCall(CeedMalloc(basis->Q * basis->P, &basis->interp));
1895 
1896     // Initialize
1897     for (CeedInt i = 0; i < basis->Q * basis->P; i++) basis->interp[i] = 1.0;
1898 
1899     // Calculate
1900     for (CeedInt d = 0; d < basis->dim; d++) {
1901       for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
1902         for (CeedInt node = 0; node < basis->P; node++) {
1903           CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
1904           CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
1905 
1906           basis->interp[qpt * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
1907         }
1908       }
1909     }
1910   }
1911   *interp = basis->interp;
1912   return CEED_ERROR_SUCCESS;
1913 }
1914 
1915 /**
1916   @brief Get 1D interpolation matrix of a tensor product `CeedBasis`
1917 
1918   @param[in]  basis     `CeedBasis`
1919   @param[out] interp_1d Variable to store interpolation matrix
1920 
1921   @return An error code: 0 - success, otherwise - failure
1922 
1923   @ref Backend
1924 **/
1925 int CeedBasisGetInterp1D(CeedBasis basis, const CeedScalar **interp_1d) {
1926   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
1927   *interp_1d = basis->interp_1d;
1928   return CEED_ERROR_SUCCESS;
1929 }
1930 
1931 /**
1932   @brief Get gradient matrix of a `CeedBasis`
1933 
1934   @param[in]  basis `CeedBasis`
1935   @param[out] grad  Variable to store gradient matrix
1936 
1937   @return An error code: 0 - success, otherwise - failure
1938 
1939   @ref Advanced
1940 **/
1941 int CeedBasisGetGrad(CeedBasis basis, const CeedScalar **grad) {
1942   if (!basis->grad && basis->is_tensor_basis) {
1943     // Allocate
1944     CeedCall(CeedMalloc(basis->dim * basis->Q * basis->P, &basis->grad));
1945 
1946     // Initialize
1947     for (CeedInt i = 0; i < basis->dim * basis->Q * basis->P; i++) basis->grad[i] = 1.0;
1948 
1949     // Calculate
1950     for (CeedInt d = 0; d < basis->dim; d++) {
1951       for (CeedInt i = 0; i < basis->dim; i++) {
1952         for (CeedInt qpt = 0; qpt < basis->Q; qpt++) {
1953           for (CeedInt node = 0; node < basis->P; node++) {
1954             CeedInt p = (node / CeedIntPow(basis->P_1d, d)) % basis->P_1d;
1955             CeedInt q = (qpt / CeedIntPow(basis->Q_1d, d)) % basis->Q_1d;
1956 
1957             if (i == d) basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->grad_1d[q * basis->P_1d + p];
1958             else basis->grad[(i * basis->Q + qpt) * (basis->P) + node] *= basis->interp_1d[q * basis->P_1d + p];
1959           }
1960         }
1961       }
1962     }
1963   }
1964   *grad = basis->grad;
1965   return CEED_ERROR_SUCCESS;
1966 }
1967 
1968 /**
1969   @brief Get 1D gradient matrix of a tensor product `CeedBasis`
1970 
1971   @param[in]  basis   `CeedBasis`
1972   @param[out] grad_1d Variable to store gradient matrix
1973 
1974   @return An error code: 0 - success, otherwise - failure
1975 
1976   @ref Advanced
1977 **/
1978 int CeedBasisGetGrad1D(CeedBasis basis, const CeedScalar **grad_1d) {
1979   CeedCheck(basis->is_tensor_basis, basis->ceed, CEED_ERROR_MINOR, "CeedBasis is not a tensor product CeedBasis");
1980   *grad_1d = basis->grad_1d;
1981   return CEED_ERROR_SUCCESS;
1982 }
1983 
1984 /**
1985   @brief Get divergence matrix of a `CeedBasis`
1986 
1987   @param[in]  basis `CeedBasis`
1988   @param[out] div   Variable to store divergence matrix
1989 
1990   @return An error code: 0 - success, otherwise - failure
1991 
1992   @ref Advanced
1993 **/
1994 int CeedBasisGetDiv(CeedBasis basis, const CeedScalar **div) {
1995   CeedCheck(basis->div, basis->ceed, CEED_ERROR_MINOR, "CeedBasis does not have divergence matrix");
1996   *div = basis->div;
1997   return CEED_ERROR_SUCCESS;
1998 }
1999 
2000 /**
2001   @brief Get curl matrix of a `CeedBasis`
2002 
2003   @param[in]  basis `CeedBasis`
2004   @param[out] curl  Variable to store curl matrix
2005 
2006   @return An error code: 0 - success, otherwise - failure
2007 
2008   @ref Advanced
2009 **/
2010 int CeedBasisGetCurl(CeedBasis basis, const CeedScalar **curl) {
2011   CeedCheck(basis->curl, basis->ceed, CEED_ERROR_MINOR, "CeedBasis does not have curl matrix");
2012   *curl = basis->curl;
2013   return CEED_ERROR_SUCCESS;
2014 }
2015 
2016 /**
2017   @brief Destroy a @ref  CeedBasis
2018 
2019   @param[in,out] basis `CeedBasis` to destroy
2020 
2021   @return An error code: 0 - success, otherwise - failure
2022 
2023   @ref User
2024 **/
2025 int CeedBasisDestroy(CeedBasis *basis) {
2026   if (!*basis || *basis == CEED_BASIS_NONE || --(*basis)->ref_count > 0) {
2027     *basis = NULL;
2028     return CEED_ERROR_SUCCESS;
2029   }
2030   if ((*basis)->Destroy) CeedCall((*basis)->Destroy(*basis));
2031   CeedCall(CeedTensorContractDestroy(&(*basis)->contract));
2032   CeedCall(CeedFree(&(*basis)->q_ref_1d));
2033   CeedCall(CeedFree(&(*basis)->q_weight_1d));
2034   CeedCall(CeedFree(&(*basis)->interp));
2035   CeedCall(CeedFree(&(*basis)->interp_1d));
2036   CeedCall(CeedFree(&(*basis)->grad));
2037   CeedCall(CeedFree(&(*basis)->grad_1d));
2038   CeedCall(CeedFree(&(*basis)->div));
2039   CeedCall(CeedFree(&(*basis)->curl));
2040   CeedCall(CeedVectorDestroy(&(*basis)->vec_chebyshev));
2041   CeedCall(CeedBasisDestroy(&(*basis)->basis_chebyshev));
2042   CeedCall(CeedDestroy(&(*basis)->ceed));
2043   CeedCall(CeedFree(basis));
2044   return CEED_ERROR_SUCCESS;
2045 }
2046 
2047 /**
2048   @brief Construct a Gauss-Legendre quadrature
2049 
2050   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-1` exactly)
2051   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2052   @param[out] q_weight_1d Array of length `Q` to hold the weights
2053 
2054   @return An error code: 0 - success, otherwise - failure
2055 
2056   @ref Utility
2057 **/
2058 int CeedGaussQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2059   CeedScalar P0, P1, P2, dP2, xi, wi, PI = 4.0 * atan(1.0);
2060 
2061   // Build q_ref_1d, q_weight_1d
2062   for (CeedInt i = 0; i <= Q / 2; i++) {
2063     // Guess
2064     xi = cos(PI * (CeedScalar)(2 * i + 1) / ((CeedScalar)(2 * Q)));
2065     // Pn(xi)
2066     P0 = 1.0;
2067     P1 = xi;
2068     P2 = 0.0;
2069     for (CeedInt j = 2; j <= Q; j++) {
2070       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2071       P0 = P1;
2072       P1 = P2;
2073     }
2074     // First Newton Step
2075     dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2076     xi  = xi - P2 / dP2;
2077     // Newton to convergence
2078     for (CeedInt k = 0; k < 100 && fabs(P2) > 10 * CEED_EPSILON; k++) {
2079       P0 = 1.0;
2080       P1 = xi;
2081       for (CeedInt j = 2; j <= Q; j++) {
2082         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2083         P0 = P1;
2084         P1 = P2;
2085       }
2086       dP2 = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2087       xi  = xi - P2 / dP2;
2088     }
2089     // Save xi, wi
2090     wi                     = 2.0 / ((1.0 - xi * xi) * dP2 * dP2);
2091     q_weight_1d[i]         = wi;
2092     q_weight_1d[Q - 1 - i] = wi;
2093     q_ref_1d[i]            = -xi;
2094     q_ref_1d[Q - 1 - i]    = xi;
2095   }
2096   return CEED_ERROR_SUCCESS;
2097 }
2098 
2099 /**
2100   @brief Construct a Gauss-Legendre-Lobatto quadrature
2101 
2102   @param[in]  Q           Number of quadrature points (integrates polynomials of degree `2*Q-3` exactly)
2103   @param[out] q_ref_1d    Array of length `Q` to hold the abscissa on `[-1, 1]`
2104   @param[out] q_weight_1d Array of length `Q` to hold the weights
2105 
2106   @return An error code: 0 - success, otherwise - failure
2107 
2108   @ref Utility
2109 **/
2110 int CeedLobattoQuadrature(CeedInt Q, CeedScalar *q_ref_1d, CeedScalar *q_weight_1d) {
2111   CeedScalar P0, P1, P2, dP2, d2P2, xi, wi, PI = 4.0 * atan(1.0);
2112 
2113   // Build q_ref_1d, q_weight_1d
2114   // Set endpoints
2115   CeedCheck(Q > 1, NULL, CEED_ERROR_DIMENSION, "Cannot create Lobatto quadrature with Q=%" CeedInt_FMT " < 2 points", Q);
2116   wi = 2.0 / ((CeedScalar)(Q * (Q - 1)));
2117   if (q_weight_1d) {
2118     q_weight_1d[0]     = wi;
2119     q_weight_1d[Q - 1] = wi;
2120   }
2121   q_ref_1d[0]     = -1.0;
2122   q_ref_1d[Q - 1] = 1.0;
2123   // Interior
2124   for (CeedInt i = 1; i <= (Q - 1) / 2; i++) {
2125     // Guess
2126     xi = cos(PI * (CeedScalar)(i) / (CeedScalar)(Q - 1));
2127     // Pn(xi)
2128     P0 = 1.0;
2129     P1 = xi;
2130     P2 = 0.0;
2131     for (CeedInt j = 2; j < Q; j++) {
2132       P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2133       P0 = P1;
2134       P1 = P2;
2135     }
2136     // First Newton step
2137     dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2138     d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2139     xi   = xi - dP2 / d2P2;
2140     // Newton to convergence
2141     for (CeedInt k = 0; k < 100 && fabs(dP2) > 10 * CEED_EPSILON; k++) {
2142       P0 = 1.0;
2143       P1 = xi;
2144       for (CeedInt j = 2; j < Q; j++) {
2145         P2 = (((CeedScalar)(2 * j - 1)) * xi * P1 - ((CeedScalar)(j - 1)) * P0) / ((CeedScalar)(j));
2146         P0 = P1;
2147         P1 = P2;
2148       }
2149       dP2  = (xi * P2 - P0) * (CeedScalar)Q / (xi * xi - 1.0);
2150       d2P2 = (2 * xi * dP2 - (CeedScalar)(Q * (Q - 1)) * P2) / (1.0 - xi * xi);
2151       xi   = xi - dP2 / d2P2;
2152     }
2153     // Save xi, wi
2154     wi = 2.0 / (((CeedScalar)(Q * (Q - 1))) * P2 * P2);
2155     if (q_weight_1d) {
2156       q_weight_1d[i]         = wi;
2157       q_weight_1d[Q - 1 - i] = wi;
2158     }
2159     q_ref_1d[i]         = -xi;
2160     q_ref_1d[Q - 1 - i] = xi;
2161   }
2162   return CEED_ERROR_SUCCESS;
2163 }
2164 
2165 /// @}
2166