Actual source code: mffd.c
1: #include <../src/mat/impls/shell/shell.h>
2: #include <../src/mat/impls/mffd/mffdimpl.h>
4: PetscFunctionList MatMFFDList = NULL;
5: PetscBool MatMFFDRegisterAllCalled = PETSC_FALSE;
7: PetscClassId MATMFFD_CLASSID;
8: PetscLogEvent MATMFFD_Mult;
10: static PetscBool MatMFFDPackageInitialized = PETSC_FALSE;
12: /*@C
13: MatMFFDFinalizePackage - This function destroys everything in the MATMFFD` package. It is
14: called from `PetscFinalize()`.
16: Level: developer
18: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `PetscFinalize()`, `MatCreateMFFD()`, `MatCreateSNESMF()`
19: @*/
20: PetscErrorCode MatMFFDFinalizePackage(void)
21: {
22: PetscFunctionBegin;
23: PetscCall(PetscFunctionListDestroy(&MatMFFDList));
24: MatMFFDPackageInitialized = PETSC_FALSE;
25: MatMFFDRegisterAllCalled = PETSC_FALSE;
26: PetscFunctionReturn(PETSC_SUCCESS);
27: }
29: /*@C
30: MatMFFDInitializePackage - This function initializes everything in the MATMFFD` package. It is called
31: from `MatInitializePackage()`.
33: Level: developer
35: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `PetscInitialize()`
36: @*/
37: PetscErrorCode MatMFFDInitializePackage(void)
38: {
39: char logList[256];
40: PetscBool opt, pkg;
42: PetscFunctionBegin;
43: if (MatMFFDPackageInitialized) PetscFunctionReturn(PETSC_SUCCESS);
44: MatMFFDPackageInitialized = PETSC_TRUE;
45: /* Register Classes */
46: PetscCall(PetscClassIdRegister("MatMFFD", &MATMFFD_CLASSID));
47: /* Register Constructors */
48: PetscCall(MatMFFDRegisterAll());
49: /* Register Events */
50: PetscCall(PetscLogEventRegister("MatMult MF", MATMFFD_CLASSID, &MATMFFD_Mult));
51: /* Process Info */
52: {
53: PetscClassId classids[1];
55: classids[0] = MATMFFD_CLASSID;
56: PetscCall(PetscInfoProcessClass("matmffd", 1, classids));
57: }
58: /* Process summary exclusions */
59: PetscCall(PetscOptionsGetString(NULL, NULL, "-log_exclude", logList, sizeof(logList), &opt));
60: if (opt) {
61: PetscCall(PetscStrInList("matmffd", logList, ',', &pkg));
62: if (pkg) PetscCall(PetscLogEventExcludeClass(MATMFFD_CLASSID));
63: }
64: /* Register package finalizer */
65: PetscCall(PetscRegisterFinalize(MatMFFDFinalizePackage));
66: PetscFunctionReturn(PETSC_SUCCESS);
67: }
69: static PetscErrorCode MatMFFDSetType_MFFD(Mat mat, MatMFFDType ftype)
70: {
71: MatMFFD ctx;
72: PetscBool match;
73: PetscErrorCode (*r)(MatMFFD);
75: PetscFunctionBegin;
77: PetscAssertPointer(ftype, 2);
78: PetscCall(MatShellGetContext(mat, &ctx));
80: /* already set, so just return */
81: PetscCall(PetscObjectTypeCompare((PetscObject)ctx, ftype, &match));
82: if (match) PetscFunctionReturn(PETSC_SUCCESS);
84: /* destroy the old one if it exists */
85: PetscTryTypeMethod(ctx, destroy);
87: PetscCall(PetscFunctionListFind(MatMFFDList, ftype, &r));
88: PetscCheck(r, PetscObjectComm((PetscObject)mat), PETSC_ERR_ARG_UNKNOWN_TYPE, "Unknown MatMFFD type %s given", ftype);
89: PetscCall((*r)(ctx));
90: PetscCall(PetscObjectChangeTypeName((PetscObject)ctx, ftype));
91: PetscFunctionReturn(PETSC_SUCCESS);
92: }
94: /*@
95: MatMFFDSetType - Sets the method that is used to compute the
96: differencing parameter for finite difference matrix-free formulations.
98: Input Parameters:
99: + mat - the "matrix-free" matrix created via `MatCreateSNESMF()`, or `MatCreateMFFD()`
100: or `MatSetType`(mat,`MATMFFD`);
101: - ftype - the type requested, either `MATMFFD_WP` or `MATMFFD_DS`
103: Level: advanced
105: Note:
106: For example, such routines can compute `h` for use in
107: Jacobian-vector products of the form
108: .vb
110: F(x+ha) - F(x)
111: F'(u)a ~= ----------------
112: h
113: .ve
115: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MATMFFD_WP`, `MATMFFD_DS`, `MatCreateSNESMF()`, `MatMFFDRegister()`, `MatMFFDSetFunction()`, `MatCreateMFFD()`
116: @*/
117: PetscErrorCode MatMFFDSetType(Mat mat, MatMFFDType ftype)
118: {
119: PetscFunctionBegin;
121: PetscAssertPointer(ftype, 2);
122: PetscTryMethod(mat, "MatMFFDSetType_C", (Mat, MatMFFDType), (mat, ftype));
123: PetscFunctionReturn(PETSC_SUCCESS);
124: }
126: static PetscErrorCode MatGetDiagonal_MFFD(Mat, Vec);
128: typedef PetscErrorCode (*FCN1)(void *, Vec); /* force argument to next function to not be extern C*/
129: static PetscErrorCode MatMFFDSetFunctioniBase_MFFD(Mat mat, FCN1 func)
130: {
131: MatMFFD ctx;
133: PetscFunctionBegin;
134: PetscCall(MatShellGetContext(mat, &ctx));
135: ctx->funcisetbase = func;
136: PetscFunctionReturn(PETSC_SUCCESS);
137: }
139: typedef PetscErrorCode (*FCN2)(void *, PetscInt, Vec, PetscScalar *); /* force argument to next function to not be extern C*/
140: static PetscErrorCode MatMFFDSetFunctioni_MFFD(Mat mat, FCN2 funci)
141: {
142: MatMFFD ctx;
144: PetscFunctionBegin;
145: PetscCall(MatShellGetContext(mat, &ctx));
146: ctx->funci = funci;
147: PetscCall(MatShellSetOperation(mat, MATOP_GET_DIAGONAL, (void (*)(void))MatGetDiagonal_MFFD));
148: PetscFunctionReturn(PETSC_SUCCESS);
149: }
151: static PetscErrorCode MatMFFDGetH_MFFD(Mat mat, PetscScalar *h)
152: {
153: MatMFFD ctx;
155: PetscFunctionBegin;
156: PetscCall(MatShellGetContext(mat, &ctx));
157: *h = ctx->currenth;
158: PetscFunctionReturn(PETSC_SUCCESS);
159: }
161: static PetscErrorCode MatMFFDResetHHistory_MFFD(Mat J)
162: {
163: MatMFFD ctx;
165: PetscFunctionBegin;
166: PetscCall(MatShellGetContext(J, &ctx));
167: ctx->ncurrenth = 0;
168: PetscFunctionReturn(PETSC_SUCCESS);
169: }
171: /*@C
172: MatMFFDRegister - Adds a method to the `MATMFFD` registry.
174: Not Collective, No Fortran Support
176: Input Parameters:
177: + sname - name of a new user-defined compute-h module
178: - function - routine to create method context
180: Level: developer
182: Note:
183: `MatMFFDRegister()` may be called multiple times to add several user-defined solvers.
185: Example Usage:
186: .vb
187: MatMFFDRegister("my_h", MyHCreate);
188: .ve
190: Then, your solver can be chosen with the procedural interface via `MatMFFDSetType`(mfctx, "my_h")` or at runtime via the option
191: `-mat_mffd_type my_h`
193: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatMFFDRegisterAll()`, `MatMFFDRegisterDestroy()`
194: @*/
195: PetscErrorCode MatMFFDRegister(const char sname[], PetscErrorCode (*function)(MatMFFD))
196: {
197: PetscFunctionBegin;
198: PetscCall(MatInitializePackage());
199: PetscCall(PetscFunctionListAdd(&MatMFFDList, sname, function));
200: PetscFunctionReturn(PETSC_SUCCESS);
201: }
203: static PetscErrorCode MatDestroy_MFFD(Mat mat)
204: {
205: MatMFFD ctx;
207: PetscFunctionBegin;
208: PetscCall(MatShellGetContext(mat, &ctx));
209: PetscCall(VecDestroy(&ctx->w));
210: PetscCall(VecDestroy(&ctx->current_u));
211: if (ctx->current_f_allocated) PetscCall(VecDestroy(&ctx->current_f));
212: PetscTryTypeMethod(ctx, destroy);
213: PetscCall(PetscHeaderDestroy(&ctx));
215: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetBase_C", NULL));
216: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetFunctioniBase_C", NULL));
217: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetFunctioni_C", NULL));
218: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetFunction_C", NULL));
219: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetFunctionError_C", NULL));
220: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetCheckh_C", NULL));
221: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetPeriod_C", NULL));
222: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDResetHHistory_C", NULL));
223: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetHHistory_C", NULL));
224: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDSetType_C", NULL));
225: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatMFFDGetH_C", NULL));
226: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatSNESMFSetReuseBase_C", NULL));
227: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatSNESMFGetReuseBase_C", NULL));
228: PetscCall(PetscObjectComposeFunction((PetscObject)mat, "MatShellSetContext_C", NULL));
229: PetscFunctionReturn(PETSC_SUCCESS);
230: }
232: /*
233: MatMFFDView_MFFD - Views matrix-free parameters.
235: */
236: static PetscErrorCode MatView_MFFD(Mat J, PetscViewer viewer)
237: {
238: MatMFFD ctx;
239: PetscBool iascii, viewbase, viewfunction;
240: const char *prefix;
242: PetscFunctionBegin;
243: PetscCall(MatShellGetContext(J, &ctx));
244: PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &iascii));
245: if (iascii) {
246: PetscCall(PetscViewerASCIIPrintf(viewer, "Matrix-free approximation:\n"));
247: PetscCall(PetscViewerASCIIPushTab(viewer));
248: PetscCall(PetscViewerASCIIPrintf(viewer, "err=%g (relative error in function evaluation)\n", (double)ctx->error_rel));
249: if (!((PetscObject)ctx)->type_name) {
250: PetscCall(PetscViewerASCIIPrintf(viewer, "The compute h routine has not yet been set\n"));
251: } else {
252: PetscCall(PetscViewerASCIIPrintf(viewer, "Using %s compute h routine\n", ((PetscObject)ctx)->type_name));
253: }
254: #if defined(PETSC_USE_COMPLEX)
255: if (ctx->usecomplex) PetscCall(PetscViewerASCIIPrintf(viewer, "Using Lyness complex number trick to compute the matrix-vector product\n"));
256: #endif
257: PetscTryTypeMethod(ctx, view, viewer);
258: PetscCall(PetscObjectGetOptionsPrefix((PetscObject)J, &prefix));
260: PetscCall(PetscOptionsHasName(((PetscObject)J)->options, prefix, "-mat_mffd_view_base", &viewbase));
261: if (viewbase) {
262: PetscCall(PetscViewerASCIIPrintf(viewer, "Base:\n"));
263: PetscCall(VecView(ctx->current_u, viewer));
264: }
265: PetscCall(PetscOptionsHasName(((PetscObject)J)->options, prefix, "-mat_mffd_view_function", &viewfunction));
266: if (viewfunction) {
267: PetscCall(PetscViewerASCIIPrintf(viewer, "Function:\n"));
268: PetscCall(VecView(ctx->current_f, viewer));
269: }
270: PetscCall(PetscViewerASCIIPopTab(viewer));
271: }
272: PetscFunctionReturn(PETSC_SUCCESS);
273: }
275: /*
276: MatAssemblyEnd_MFFD - Resets the ctx->ncurrenth to zero. This
277: allows the user to indicate the beginning of a new linear solve by calling
278: MatAssemblyXXX() on the matrix-free matrix. This then allows the
279: MatCreateMFFD_WP() to properly compute ||U|| only the first time
280: in the linear solver rather than every time.
282: This function is referenced directly from MatAssemblyEnd_SNESMF(), which may be in a different shared library hence
283: it must be labeled as PETSC_EXTERN
284: */
285: PETSC_EXTERN PetscErrorCode MatAssemblyEnd_MFFD(Mat J, MatAssemblyType mt)
286: {
287: MatMFFD j;
289: PetscFunctionBegin;
290: PetscCall(MatShellGetContext(J, &j));
291: PetscCall(MatMFFDResetHHistory(J));
292: PetscFunctionReturn(PETSC_SUCCESS);
293: }
295: /*
296: MatMult_MFFD - Default matrix-free form for Jacobian-vector product, y = F'(u)*a:
298: y ~= (F(u + ha) - F(u))/h,
299: where F = nonlinear function, as set by SNESSetFunction()
300: u = current iterate
301: h = difference interval
302: */
303: static PetscErrorCode MatMult_MFFD(Mat mat, Vec a, Vec y)
304: {
305: MatMFFD ctx;
306: PetscScalar h;
307: Vec w, U, F;
308: PetscBool zeroa;
310: PetscFunctionBegin;
311: PetscCall(MatShellGetContext(mat, &ctx));
312: PetscCheck(ctx->current_u, PetscObjectComm((PetscObject)mat), PETSC_ERR_ARG_WRONGSTATE, "MatMFFDSetBase() has not been called, this is often caused by forgetting to call MatAssemblyBegin/End on the first Mat in the SNES compute function");
313: /* We log matrix-free matrix-vector products separately, so that we can
314: separate the performance monitoring from the cases that use conventional
315: storage. We may eventually modify event logging to associate events
316: with particular objects, hence alleviating the more general problem. */
317: PetscCall(PetscLogEventBegin(MATMFFD_Mult, a, y, 0, 0));
319: w = ctx->w;
320: U = ctx->current_u;
321: F = ctx->current_f;
322: /*
323: Compute differencing parameter
324: */
325: if (!((PetscObject)ctx)->type_name) {
326: PetscCall(MatMFFDSetType(mat, MATMFFD_WP));
327: PetscCall(MatSetFromOptions(mat));
328: }
329: PetscUseTypeMethod(ctx, compute, U, a, &h, &zeroa);
330: if (zeroa) {
331: PetscCall(VecSet(y, 0.0));
332: PetscCall(PetscLogEventEnd(MATMFFD_Mult, a, y, 0, 0));
333: PetscFunctionReturn(PETSC_SUCCESS);
334: }
336: PetscCheck(!mat->erroriffailure || !PetscIsInfOrNanScalar(h), PETSC_COMM_SELF, PETSC_ERR_PLIB, "Computed Nan differencing parameter h");
337: if (ctx->checkh) PetscCall((*ctx->checkh)(ctx->checkhctx, U, a, &h));
339: /* keep a record of the current differencing parameter h */
340: ctx->currenth = h;
341: #if defined(PETSC_USE_COMPLEX)
342: PetscCall(PetscInfo(mat, "Current differencing parameter: %g + %g i\n", (double)PetscRealPart(h), (double)PetscImaginaryPart(h)));
343: #else
344: PetscCall(PetscInfo(mat, "Current differencing parameter: %15.12e\n", (double)PetscRealPart(h)));
345: #endif
346: if (ctx->historyh && ctx->ncurrenth < ctx->maxcurrenth) ctx->historyh[ctx->ncurrenth] = h;
347: ctx->ncurrenth++;
349: #if defined(PETSC_USE_COMPLEX)
350: if (ctx->usecomplex) h = PETSC_i * h;
351: #endif
353: /* w = u + ha */
354: PetscCall(VecWAXPY(w, h, a, U));
356: /* compute func(U) as base for differencing; only needed first time in and not when provided by user */
357: if (ctx->ncurrenth == 1 && ctx->current_f_allocated) PetscCall((*ctx->func)(ctx->funcctx, U, F));
358: PetscCall((*ctx->func)(ctx->funcctx, w, y));
360: #if defined(PETSC_USE_COMPLEX)
361: if (ctx->usecomplex) {
362: PetscCall(VecImaginaryPart(y));
363: h = PetscImaginaryPart(h);
364: } else {
365: PetscCall(VecAXPY(y, -1.0, F));
366: }
367: #else
368: PetscCall(VecAXPY(y, -1.0, F));
369: #endif
370: PetscCall(VecScale(y, 1.0 / h));
371: if (mat->nullsp) PetscCall(MatNullSpaceRemove(mat->nullsp, y));
373: PetscCall(PetscLogEventEnd(MATMFFD_Mult, a, y, 0, 0));
374: PetscFunctionReturn(PETSC_SUCCESS);
375: }
377: /*
378: MatGetDiagonal_MFFD - Gets the diagonal for a matrix-free matrix
380: y ~= (F(u + ha) - F(u))/h,
381: where F = nonlinear function, as set by SNESSetFunction()
382: u = current iterate
383: h = difference interval
384: */
385: static PetscErrorCode MatGetDiagonal_MFFD(Mat mat, Vec a)
386: {
387: MatMFFD ctx;
388: PetscScalar h, *aa, *ww, v;
389: PetscReal epsilon = PETSC_SQRT_MACHINE_EPSILON, umin = 100.0 * PETSC_SQRT_MACHINE_EPSILON;
390: Vec w, U;
391: PetscInt i, rstart, rend;
393: PetscFunctionBegin;
394: PetscCall(MatShellGetContext(mat, &ctx));
395: PetscCheck(ctx->func, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Requires calling MatMFFDSetFunction() first");
396: PetscCheck(ctx->funci, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Requires calling MatMFFDSetFunctioni() first");
397: w = ctx->w;
398: U = ctx->current_u;
399: PetscCall((*ctx->func)(ctx->funcctx, U, a));
400: if (ctx->funcisetbase) PetscCall((*ctx->funcisetbase)(ctx->funcctx, U));
401: PetscCall(VecCopy(U, w));
403: PetscCall(VecGetOwnershipRange(a, &rstart, &rend));
404: PetscCall(VecGetArray(a, &aa));
405: for (i = rstart; i < rend; i++) {
406: PetscCall(VecGetArray(w, &ww));
407: h = ww[i - rstart];
408: if (h == 0.0) h = 1.0;
409: if (PetscAbsScalar(h) < umin && PetscRealPart(h) >= 0.0) h = umin;
410: else if (PetscRealPart(h) < 0.0 && PetscAbsScalar(h) < umin) h = -umin;
411: h *= epsilon;
413: ww[i - rstart] += h;
414: PetscCall(VecRestoreArray(w, &ww));
415: PetscCall((*ctx->funci)(ctx->funcctx, i, w, &v));
416: aa[i - rstart] = (v - aa[i - rstart]) / h;
418: PetscCall(VecGetArray(w, &ww));
419: ww[i - rstart] -= h;
420: PetscCall(VecRestoreArray(w, &ww));
421: }
422: PetscCall(VecRestoreArray(a, &aa));
423: PetscFunctionReturn(PETSC_SUCCESS);
424: }
426: PETSC_EXTERN PetscErrorCode MatMFFDSetBase_MFFD(Mat J, Vec U, Vec F)
427: {
428: MatMFFD ctx;
430: PetscFunctionBegin;
431: PetscCall(MatShellGetContext(J, &ctx));
432: PetscCall(MatMFFDResetHHistory(J));
433: if (!ctx->current_u) {
434: PetscCall(VecDuplicate(U, &ctx->current_u));
435: PetscCall(VecLockReadPush(ctx->current_u));
436: }
437: PetscCall(VecLockReadPop(ctx->current_u));
438: PetscCall(VecCopy(U, ctx->current_u));
439: PetscCall(VecLockReadPush(ctx->current_u));
440: if (F) {
441: if (ctx->current_f_allocated) PetscCall(VecDestroy(&ctx->current_f));
442: ctx->current_f = F;
443: ctx->current_f_allocated = PETSC_FALSE;
444: } else if (!ctx->current_f_allocated) {
445: PetscCall(MatCreateVecs(J, NULL, &ctx->current_f));
446: ctx->current_f_allocated = PETSC_TRUE;
447: }
448: if (!ctx->w) PetscCall(VecDuplicate(ctx->current_u, &ctx->w));
449: J->assembled = PETSC_TRUE;
450: PetscFunctionReturn(PETSC_SUCCESS);
451: }
453: typedef PetscErrorCode (*FCN3)(void *, Vec, Vec, PetscScalar *); /* force argument to next function to not be extern C*/
455: static PetscErrorCode MatMFFDSetCheckh_MFFD(Mat J, FCN3 fun, void *ectx)
456: {
457: MatMFFD ctx;
459: PetscFunctionBegin;
460: PetscCall(MatShellGetContext(J, &ctx));
461: ctx->checkh = fun;
462: ctx->checkhctx = ectx;
463: PetscFunctionReturn(PETSC_SUCCESS);
464: }
466: /*@
467: MatMFFDSetOptionsPrefix - Sets the prefix used for searching for all
468: MATMFFD` options in the database.
470: Collective
472: Input Parameters:
473: + mat - the `MATMFFD` context
474: - prefix - the prefix to prepend to all option names
476: Note:
477: A hyphen (-) must NOT be given at the beginning of the prefix name.
478: The first character of all runtime options is AUTOMATICALLY the hyphen.
480: Level: advanced
482: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatSetFromOptions()`, `MatCreateSNESMF()`, `MatCreateMFFD()`
483: @*/
484: PetscErrorCode MatMFFDSetOptionsPrefix(Mat mat, const char prefix[])
485: {
486: MatMFFD mfctx;
488: PetscFunctionBegin;
490: PetscCall(MatShellGetContext(mat, &mfctx));
492: PetscCall(PetscObjectSetOptionsPrefix((PetscObject)mfctx, prefix));
493: PetscFunctionReturn(PETSC_SUCCESS);
494: }
496: static PetscErrorCode MatSetFromOptions_MFFD(Mat mat, PetscOptionItems *PetscOptionsObject)
497: {
498: MatMFFD mfctx;
499: PetscBool flg;
500: char ftype[256];
502: PetscFunctionBegin;
503: PetscCall(MatShellGetContext(mat, &mfctx));
505: PetscObjectOptionsBegin((PetscObject)mfctx);
506: PetscCall(PetscOptionsFList("-mat_mffd_type", "Matrix free type", "MatMFFDSetType", MatMFFDList, ((PetscObject)mfctx)->type_name, ftype, 256, &flg));
507: if (flg) PetscCall(MatMFFDSetType(mat, ftype));
509: PetscCall(PetscOptionsReal("-mat_mffd_err", "set sqrt relative error in function", "MatMFFDSetFunctionError", mfctx->error_rel, &mfctx->error_rel, NULL));
510: PetscCall(PetscOptionsInt("-mat_mffd_period", "how often h is recomputed", "MatMFFDSetPeriod", mfctx->recomputeperiod, &mfctx->recomputeperiod, NULL));
512: flg = PETSC_FALSE;
513: PetscCall(PetscOptionsBool("-mat_mffd_check_positivity", "Insure that U + h*a is nonnegative", "MatMFFDSetCheckh", flg, &flg, NULL));
514: if (flg) PetscCall(MatMFFDSetCheckh(mat, MatMFFDCheckPositivity, NULL));
515: #if defined(PETSC_USE_COMPLEX)
516: PetscCall(PetscOptionsBool("-mat_mffd_complex", "Use Lyness complex number trick to compute the matrix-vector product", "None", mfctx->usecomplex, &mfctx->usecomplex, NULL));
517: #endif
518: PetscTryTypeMethod(mfctx, setfromoptions, PetscOptionsObject);
519: PetscOptionsEnd();
520: PetscFunctionReturn(PETSC_SUCCESS);
521: }
523: static PetscErrorCode MatMFFDSetPeriod_MFFD(Mat mat, PetscInt period)
524: {
525: MatMFFD ctx;
527: PetscFunctionBegin;
528: PetscCall(MatShellGetContext(mat, &ctx));
529: ctx->recomputeperiod = period;
530: PetscFunctionReturn(PETSC_SUCCESS);
531: }
533: static PetscErrorCode MatMFFDSetFunction_MFFD(Mat mat, PetscErrorCode (*func)(void *, Vec, Vec), void *funcctx)
534: {
535: MatMFFD ctx;
537: PetscFunctionBegin;
538: PetscCall(MatShellGetContext(mat, &ctx));
539: ctx->func = func;
540: ctx->funcctx = funcctx;
541: PetscFunctionReturn(PETSC_SUCCESS);
542: }
544: static PetscErrorCode MatMFFDSetFunctionError_MFFD(Mat mat, PetscReal error)
545: {
546: PetscFunctionBegin;
547: if (error != (PetscReal)PETSC_DEFAULT) {
548: MatMFFD ctx;
550: PetscCall(MatShellGetContext(mat, &ctx));
551: ctx->error_rel = error;
552: }
553: PetscFunctionReturn(PETSC_SUCCESS);
554: }
556: static PetscErrorCode MatMFFDSetHHistory_MFFD(Mat J, PetscScalar history[], PetscInt nhistory)
557: {
558: MatMFFD ctx;
560: PetscFunctionBegin;
561: PetscCall(MatShellGetContext(J, &ctx));
562: ctx->historyh = history;
563: ctx->maxcurrenth = nhistory;
564: ctx->currenth = 0.;
565: PetscFunctionReturn(PETSC_SUCCESS);
566: }
568: /*MC
569: MATMFFD - "mffd" - A matrix-free matrix type.
571: Level: advanced
573: Developer Notes:
574: This is implemented on top of `MATSHELL` to get support for scaling and shifting without requiring duplicate code
576: Users should not MatShell... operations on this class, there is some error checking for that incorrect usage
578: .seealso: [](ch_matrices), `Mat`, `MatCreateMFFD()`, `MatCreateSNESMF()`, `MatMFFDSetFunction()`, `MatMFFDSetType()`,
579: `MatMFFDSetFunctionError()`, `MatMFFDDSSetUmin()`, `MatMFFDSetFunction()`
580: `MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`, `MatCreateSNESMF()`,
581: `MatMFFDGetH()`,
582: M*/
583: PETSC_EXTERN PetscErrorCode MatCreate_MFFD(Mat A)
584: {
585: MatMFFD mfctx;
587: PetscFunctionBegin;
588: PetscCall(MatMFFDInitializePackage());
590: PetscCall(PetscHeaderCreate(mfctx, MATMFFD_CLASSID, "MatMFFD", "Matrix-free Finite Differencing", "Mat", PetscObjectComm((PetscObject)A), NULL, NULL));
592: mfctx->error_rel = PETSC_SQRT_MACHINE_EPSILON;
593: mfctx->recomputeperiod = 1;
594: mfctx->count = 0;
595: mfctx->currenth = 0.0;
596: mfctx->historyh = NULL;
597: mfctx->ncurrenth = 0;
598: mfctx->maxcurrenth = 0;
599: ((PetscObject)mfctx)->type_name = NULL;
601: /*
602: Create the empty data structure to contain compute-h routines.
603: These will be filled in below from the command line options or
604: a later call with MatMFFDSetType() or if that is not called
605: then it will default in the first use of MatMult_MFFD()
606: */
607: mfctx->ops->compute = NULL;
608: mfctx->ops->destroy = NULL;
609: mfctx->ops->view = NULL;
610: mfctx->ops->setfromoptions = NULL;
611: mfctx->hctx = NULL;
613: mfctx->func = NULL;
614: mfctx->funcctx = NULL;
615: mfctx->w = NULL;
616: mfctx->mat = A;
618: PetscCall(MatSetType(A, MATSHELL));
619: PetscCall(MatShellSetContext(A, mfctx));
620: PetscCall(MatShellSetOperation(A, MATOP_MULT, (void (*)(void))MatMult_MFFD));
621: PetscCall(MatShellSetOperation(A, MATOP_DESTROY, (void (*)(void))MatDestroy_MFFD));
622: PetscCall(MatShellSetOperation(A, MATOP_VIEW, (void (*)(void))MatView_MFFD));
623: PetscCall(MatShellSetOperation(A, MATOP_ASSEMBLY_END, (void (*)(void))MatAssemblyEnd_MFFD));
624: PetscCall(MatShellSetOperation(A, MATOP_SET_FROM_OPTIONS, (void (*)(void))MatSetFromOptions_MFFD));
625: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatShellSetContext_C", MatShellSetContext_Immutable));
626: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatShellSetContextDestroy_C", MatShellSetContextDestroy_Immutable));
627: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatShellSetManageScalingShifts_C", MatShellSetManageScalingShifts_Immutable));
629: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetBase_C", MatMFFDSetBase_MFFD));
630: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetFunctioniBase_C", MatMFFDSetFunctioniBase_MFFD));
631: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetFunctioni_C", MatMFFDSetFunctioni_MFFD));
632: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetFunction_C", MatMFFDSetFunction_MFFD));
633: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetCheckh_C", MatMFFDSetCheckh_MFFD));
634: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetPeriod_C", MatMFFDSetPeriod_MFFD));
635: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetFunctionError_C", MatMFFDSetFunctionError_MFFD));
636: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDResetHHistory_C", MatMFFDResetHHistory_MFFD));
637: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetHHistory_C", MatMFFDSetHHistory_MFFD));
638: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDSetType_C", MatMFFDSetType_MFFD));
639: PetscCall(PetscObjectComposeFunction((PetscObject)A, "MatMFFDGetH_C", MatMFFDGetH_MFFD));
640: PetscCall(PetscObjectChangeTypeName((PetscObject)A, MATMFFD));
641: PetscFunctionReturn(PETSC_SUCCESS);
642: }
644: /*@
645: MatCreateMFFD - Creates a matrix-free matrix of type `MATMFFD`. See also `MatCreateSNESMF()`
647: Collective
649: Input Parameters:
650: + comm - MPI communicator
651: . m - number of local rows (or `PETSC_DECIDE` to have calculated if `M` is given)
652: This value should be the same as the local size used in creating the
653: y vector for the matrix-vector product y = Ax.
654: . n - This value should be the same as the local size used in creating the
655: x vector for the matrix-vector product y = Ax. (or `PETSC_DECIDE` to have
656: calculated if `N` is given) For square matrices `n` is almost always `m`.
657: . M - number of global rows (or `PETSC_DETERMINE` to have calculated if `m` is given)
658: - N - number of global columns (or `PETSC_DETERMINE` to have calculated if `n` is given)
660: Output Parameter:
661: . J - the matrix-free matrix
663: Options Database Keys:
664: + -mat_mffd_type - wp or ds (see `MATMFFD_WP` or `MATMFFD_DS`)
665: . -mat_mffd_err - square root of estimated relative error in function evaluation
666: . -mat_mffd_period - how often h is recomputed, defaults to 1, every time
667: . -mat_mffd_check_positivity - possibly decrease `h` until U + h*a has only positive values
668: . -mat_mffd_umin <umin> - Sets umin (for default PETSc routine that computes h only)
669: - -mat_mffd_complex - use the Lyness trick with complex numbers to compute the matrix-vector product instead of differencing
670: (requires real valued functions but that PETSc be configured for complex numbers)
672: Level: advanced
674: Notes:
675: The matrix-free matrix context merely contains the function pointers
676: and work space for performing finite difference approximations of
677: Jacobian-vector products, F'(u)*a,
679: The default code uses the following approach to compute h
681: .vb
682: F'(u)*a = [F(u+h*a) - F(u)]/h where
683: h = error_rel*u'a/||a||^2 if |u'a| > umin*||a||_{1}
684: = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2 otherwise
685: where
686: error_rel = square root of relative error in function evaluation
687: umin = minimum iterate parameter
688: .ve
690: You can call `SNESSetJacobian()` with `MatMFFDComputeJacobian()` if you are using matrix and not a different
691: preconditioner matrix
693: The user can set the error_rel via `MatMFFDSetFunctionError()` and
694: umin via `MatMFFDDSSetUmin()`.
696: The user should call `MatDestroy()` when finished with the matrix-free
697: matrix context.
699: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatDestroy()`, `MatMFFDSetFunctionError()`, `MatMFFDDSSetUmin()`, `MatMFFDSetFunction()`
700: `MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`, `MatCreateSNESMF()`,
701: `MatMFFDGetH()`, `MatMFFDRegister()`, `MatMFFDComputeJacobian()`
702: @*/
703: PetscErrorCode MatCreateMFFD(MPI_Comm comm, PetscInt m, PetscInt n, PetscInt M, PetscInt N, Mat *J)
704: {
705: PetscFunctionBegin;
706: PetscCall(MatCreate(comm, J));
707: PetscCall(MatSetSizes(*J, m, n, M, N));
708: PetscCall(MatSetType(*J, MATMFFD));
709: PetscCall(MatSetUp(*J));
710: PetscFunctionReturn(PETSC_SUCCESS);
711: }
713: /*@
714: MatMFFDGetH - Gets the last value that was used as the differencing for a `MATMFFD` matrix
715: parameter.
717: Not Collective
719: Input Parameters:
720: . mat - the `MATMFFD` matrix
722: Output Parameter:
723: . h - the differencing step size
725: Level: advanced
727: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatCreateSNESMF()`, `MatMFFDSetHHistory()`, `MatCreateMFFD()`, `MatMFFDResetHHistory()`
728: @*/
729: PetscErrorCode MatMFFDGetH(Mat mat, PetscScalar *h)
730: {
731: PetscFunctionBegin;
733: PetscAssertPointer(h, 2);
734: PetscUseMethod(mat, "MatMFFDGetH_C", (Mat, PetscScalar *), (mat, h));
735: PetscFunctionReturn(PETSC_SUCCESS);
736: }
738: /*@C
739: MatMFFDSetFunction - Sets the function used in applying the matrix-free `MATMFFD` matrix.
741: Logically Collective
743: Input Parameters:
744: + mat - the matrix-free matrix `MATMFFD` created via `MatCreateSNESMF()` or `MatCreateMFFD()`
745: . func - the function to use
746: - funcctx - optional function context passed to function
748: Calling sequence of `func`:
749: + funcctx - user provided context
750: . x - input vector
751: - f - computed output function
753: Level: advanced
755: Notes:
756: If you use this you MUST call `MatAssemblyBegin()` and `MatAssemblyEnd()` on the matrix-free
757: matrix inside your compute Jacobian routine
759: If this is not set then it will use the function set with `SNESSetFunction()` if `MatCreateSNESMF()` was used.
761: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatCreateSNESMF()`, `MatMFFDGetH()`, `MatCreateMFFD()`,
762: `MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`, `SNESSetFunction()`
763: @*/
764: PetscErrorCode MatMFFDSetFunction(Mat mat, PetscErrorCode (*func)(void *funcctx, Vec x, Vec f), void *funcctx)
765: {
766: PetscFunctionBegin;
768: PetscTryMethod(mat, "MatMFFDSetFunction_C", (Mat, PetscErrorCode (*)(void *, Vec, Vec), void *), (mat, func, funcctx));
769: PetscFunctionReturn(PETSC_SUCCESS);
770: }
772: /*@C
773: MatMFFDSetFunctioni - Sets the function for a single component for a `MATMFFD` matrix
775: Logically Collective
777: Input Parameters:
778: + mat - the matrix-free matrix `MATMFFD`
779: - funci - the function to use
781: Level: advanced
783: Notes:
784: If you use this you MUST call `MatAssemblyBegin()` and `MatAssemblyEnd()` on the matrix-free
785: matrix inside your compute Jacobian routine.
787: This function is necessary to compute the diagonal of the matrix.
788: funci must not contain any MPI call as it is called inside a loop on the local portion of the vector.
790: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatCreateSNESMF()`, `MatMFFDGetH()`, `MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`, `SNESetFunction()`, `MatGetDiagonal()`
791: @*/
792: PetscErrorCode MatMFFDSetFunctioni(Mat mat, PetscErrorCode (*funci)(void *, PetscInt, Vec, PetscScalar *))
793: {
794: PetscFunctionBegin;
796: PetscTryMethod(mat, "MatMFFDSetFunctioni_C", (Mat, PetscErrorCode (*)(void *, PetscInt, Vec, PetscScalar *)), (mat, funci));
797: PetscFunctionReturn(PETSC_SUCCESS);
798: }
800: /*@C
801: MatMFFDSetFunctioniBase - Sets the base vector for a single component function evaluation for a `MATMFFD` matrix
803: Logically Collective
805: Input Parameters:
806: + mat - the `MATMFFD` matrix-free matrix
807: - func - the function to use
809: Level: advanced
811: Notes:
812: If you use this you MUST call `MatAssemblyBegin()` and `MatAssemblyEnd()` on the matrix-free
813: matrix inside your compute Jacobian routine.
815: This function is necessary to compute the diagonal of the matrix, used for example with `PCJACOBI`
817: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatCreateSNESMF()`, `MatMFFDGetH()`, `MatCreateMFFD()`,
818: `MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`, `SNESetFunction()`, `MatGetDiagonal()`
819: @*/
820: PetscErrorCode MatMFFDSetFunctioniBase(Mat mat, PetscErrorCode (*func)(void *, Vec))
821: {
822: PetscFunctionBegin;
824: PetscTryMethod(mat, "MatMFFDSetFunctioniBase_C", (Mat, PetscErrorCode (*)(void *, Vec)), (mat, func));
825: PetscFunctionReturn(PETSC_SUCCESS);
826: }
828: /*@
829: MatMFFDSetPeriod - Sets how often h is recomputed for a `MATMFFD` matrix, by default it is every time
831: Logically Collective
833: Input Parameters:
834: + mat - the `MATMFFD` matrix-free matrix
835: - period - 1 for every time, 2 for every second etc
837: Options Database Key:
838: . -mat_mffd_period <period> - Sets how often `h` is recomputed
840: Level: advanced
842: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatCreateSNESMF()`, `MatMFFDGetH()`,
843: `MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`
844: @*/
845: PetscErrorCode MatMFFDSetPeriod(Mat mat, PetscInt period)
846: {
847: PetscFunctionBegin;
850: PetscTryMethod(mat, "MatMFFDSetPeriod_C", (Mat, PetscInt), (mat, period));
851: PetscFunctionReturn(PETSC_SUCCESS);
852: }
854: /*@
855: MatMFFDSetFunctionError - Sets the error_rel for the approximation of matrix-vector products using finite differences with the `MATMFFD` matrix
857: Logically Collective
859: Input Parameters:
860: + mat - the `MATMFFD` matrix-free matrix
861: - error - relative error (should be set to the square root of the relative error in the function evaluations)
863: Options Database Key:
864: . -mat_mffd_err <error_rel> - Sets error_rel
866: Level: advanced
868: Note:
869: The default matrix-free matrix-vector product routine computes
870: .vb
871: F'(u)*a = [F(u+h*a) - F(u)]/h where
872: h = error_rel*u'a/||a||^2 if |u'a| > umin*||a||_{1}
873: = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2 else
874: .ve
876: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatCreateSNESMF()`, `MatMFFDGetH()`, `MatCreateMFFD()`,
877: `MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`
878: @*/
879: PetscErrorCode MatMFFDSetFunctionError(Mat mat, PetscReal error)
880: {
881: PetscFunctionBegin;
884: PetscTryMethod(mat, "MatMFFDSetFunctionError_C", (Mat, PetscReal), (mat, error));
885: PetscFunctionReturn(PETSC_SUCCESS);
886: }
888: /*@
889: MatMFFDSetHHistory - Sets an array to collect a history of the
890: differencing values (h) computed for the matrix-free product `MATMFFD` matrix
892: Logically Collective
894: Input Parameters:
895: + J - the `MATMFFD` matrix-free matrix
896: . history - space to hold the history
897: - nhistory - number of entries in history, if more entries are generated than
898: nhistory, then the later ones are discarded
900: Level: advanced
902: Note:
903: Use `MatMFFDResetHHistory()` to reset the history counter and collect
904: a new batch of differencing parameters, h.
906: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatMFFDGetH()`, `MatCreateSNESMF()`,
907: `MatMFFDResetHHistory()`, `MatMFFDSetFunctionError()`
908: @*/
909: PetscErrorCode MatMFFDSetHHistory(Mat J, PetscScalar history[], PetscInt nhistory)
910: {
911: PetscFunctionBegin;
913: if (history) PetscAssertPointer(history, 2);
915: PetscUseMethod(J, "MatMFFDSetHHistory_C", (Mat, PetscScalar[], PetscInt), (J, history, nhistory));
916: PetscFunctionReturn(PETSC_SUCCESS);
917: }
919: /*@
920: MatMFFDResetHHistory - Resets the counter to zero to begin
921: collecting a new set of differencing histories for the `MATMFFD` matrix
923: Logically Collective
925: Input Parameter:
926: . J - the matrix-free matrix context
928: Level: advanced
930: Note:
931: Use `MatMFFDSetHHistory()` to create the original history counter.
933: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatMFFDGetH()`, `MatCreateSNESMF()`,
934: `MatMFFDSetHHistory()`, `MatMFFDSetFunctionError()`
935: @*/
936: PetscErrorCode MatMFFDResetHHistory(Mat J)
937: {
938: PetscFunctionBegin;
940: PetscTryMethod(J, "MatMFFDResetHHistory_C", (Mat), (J));
941: PetscFunctionReturn(PETSC_SUCCESS);
942: }
944: /*@
945: MatMFFDSetBase - Sets the vector `U` at which matrix vector products of the
946: Jacobian are computed for the `MATMFFD` matrix
948: Logically Collective
950: Input Parameters:
951: + J - the `MATMFFD` matrix
952: . U - the vector
953: - F - (optional) vector that contains F(u) if it has been already computed
955: Level: advanced
957: Notes:
958: This is rarely used directly
960: If `F` is provided then it is not recomputed. Otherwise the function is evaluated at the base
961: point during the first `MatMult()` after each call to `MatMFFDSetBase()`.
963: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatMult()`
964: @*/
965: PetscErrorCode MatMFFDSetBase(Mat J, Vec U, Vec F)
966: {
967: PetscFunctionBegin;
971: PetscTryMethod(J, "MatMFFDSetBase_C", (Mat, Vec, Vec), (J, U, F));
972: PetscFunctionReturn(PETSC_SUCCESS);
973: }
975: /*@C
976: MatMFFDSetCheckh - Sets a function that checks the computed h and adjusts
977: it to satisfy some criteria for the `MATMFFD` matrix
979: Logically Collective
981: Input Parameters:
982: + J - the `MATMFFD` matrix
983: . fun - the function that checks `h`
984: - ctx - any context needed by the function
986: Options Database Keys:
987: . -mat_mffd_check_positivity <bool> - Insure that U + h*a is non-negative
989: Level: advanced
991: Notes:
992: For example, `MatMFFDCheckPositivity()` insures that all entries of U + h*a are non-negative
994: The function you provide is called after the default `h` has been computed and allows you to
995: modify it.
997: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatMFFDCheckPositivity()`
998: @*/
999: PetscErrorCode MatMFFDSetCheckh(Mat J, PetscErrorCode (*fun)(void *, Vec, Vec, PetscScalar *), void *ctx)
1000: {
1001: PetscFunctionBegin;
1003: PetscTryMethod(J, "MatMFFDSetCheckh_C", (Mat, PetscErrorCode (*)(void *, Vec, Vec, PetscScalar *), void *), (J, fun, ctx));
1004: PetscFunctionReturn(PETSC_SUCCESS);
1005: }
1007: /*@
1008: MatMFFDCheckPositivity - Checks that all entries in U + h*a are positive or
1009: zero, decreases h until this is satisfied for a `MATMFFD` matrix
1011: Logically Collective
1013: Input Parameters:
1014: + U - base vector that is added to
1015: . a - vector that is added
1016: . h - scaling factor on a
1017: - dummy - context variable (unused)
1019: Options Database Keys:
1020: . -mat_mffd_check_positivity <bool> - Insure that U + h*a is nonnegative
1022: Level: advanced
1024: Note:
1025: This is rarely used directly, rather it is passed as an argument to `MatMFFDSetCheckh()`
1027: .seealso: [](ch_matrices), `Mat`, `MATMFFD`, `MatMFFDSetCheckh()`
1028: @*/
1029: PetscErrorCode MatMFFDCheckPositivity(void *dummy, Vec U, Vec a, PetscScalar *h)
1030: {
1031: PetscReal val, minval;
1032: PetscScalar *u_vec, *a_vec;
1033: PetscInt i, n;
1034: MPI_Comm comm;
1036: PetscFunctionBegin;
1039: PetscAssertPointer(h, 4);
1040: PetscCall(PetscObjectGetComm((PetscObject)U, &comm));
1041: PetscCall(VecGetArray(U, &u_vec));
1042: PetscCall(VecGetArray(a, &a_vec));
1043: PetscCall(VecGetLocalSize(U, &n));
1044: minval = PetscAbsScalar(*h) * PetscRealConstant(1.01);
1045: for (i = 0; i < n; i++) {
1046: if (PetscRealPart(u_vec[i] + *h * a_vec[i]) <= 0.0) {
1047: val = PetscAbsScalar(u_vec[i] / a_vec[i]);
1048: if (val < minval) minval = val;
1049: }
1050: }
1051: PetscCall(VecRestoreArray(U, &u_vec));
1052: PetscCall(VecRestoreArray(a, &a_vec));
1053: PetscCallMPI(MPIU_Allreduce(&minval, &val, 1, MPIU_REAL, MPIU_MIN, comm));
1054: if (val <= PetscAbsScalar(*h)) {
1055: val = 0.99 * val;
1056: PetscCall(PetscInfo(U, "Scaling back h from %g to %g\n", (double)PetscRealPart(*h), (double)val));
1057: if (PetscRealPart(*h) > 0.0) *h = val;
1058: else *h = -val;
1059: }
1060: PetscFunctionReturn(PETSC_SUCCESS);
1061: }