Actual source code: gcr.c
2: #include <petsc/private/kspimpl.h>
4: typedef struct {
5: PetscInt restart;
6: PetscInt n_restarts;
7: PetscScalar *val;
8: Vec *VV, *SS;
9: Vec R;
11: PetscErrorCode (*modifypc)(KSP,PetscInt,PetscReal,void*); /* function to modify the preconditioner*/
12: PetscErrorCode (*modifypc_destroy)(void*); /* function to destroy the user context for the modifypc function */
14: void *modifypc_ctx; /* user defined data for the modifypc function */
15: } KSP_GCR;
17: static PetscErrorCode KSPSolve_GCR_cycle(KSP ksp)
18: {
19: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
21: PetscScalar r_dot_v;
22: Mat A, B;
23: PC pc;
24: Vec s,v,r;
25: /*
26: The residual norm will not be computed when ksp->its > ksp->chknorm hence need to initialize norm_r with some dummy value
27: */
28: PetscReal norm_r = 0.0,nrm;
29: PetscInt k, i, restart;
30: Vec x;
33: restart = ctx->restart;
34: KSPGetPC(ksp, &pc);
35: KSPGetOperators(ksp, &A, &B);
37: x = ksp->vec_sol;
38: r = ctx->R;
40: for (k=0; k<restart; k++) {
41: v = ctx->VV[k];
42: s = ctx->SS[k];
43: if (ctx->modifypc) {
44: (*ctx->modifypc)(ksp,ksp->its,ksp->rnorm,ctx->modifypc_ctx);
45: }
47: KSP_PCApply(ksp, r, s); /* s = B^{-1} r */
48: KSP_MatMult(ksp,A, s, v); /* v = A s */
50: VecMDot(v,k, ctx->VV, ctx->val);
51: for (i=0; i<k; i++) ctx->val[i] = -ctx->val[i];
52: VecMAXPY(v,k,ctx->val,ctx->VV); /* v = v - sum_{i=0}^{k-1} alpha_i v_i */
53: VecMAXPY(s,k,ctx->val,ctx->SS); /* s = s - sum_{i=0}^{k-1} alpha_i s_i */
55: VecDotNorm2(r,v,&r_dot_v,&nrm);
56: nrm = PetscSqrtReal(nrm);
57: r_dot_v = r_dot_v/nrm;
58: VecScale(v, 1.0/nrm);
59: VecScale(s, 1.0/nrm);
60: VecAXPY(x, r_dot_v, s);
61: VecAXPY(r, -r_dot_v, v);
62: if (ksp->its > ksp->chknorm && ksp->normtype != KSP_NORM_NONE) {
63: VecNorm(r, NORM_2, &norm_r);
64: KSPCheckNorm(ksp,norm_r);
65: }
66: /* update the local counter and the global counter */
67: ksp->its++;
68: ksp->rnorm = norm_r;
70: KSPLogResidualHistory(ksp,norm_r);
71: KSPMonitor(ksp,ksp->its,norm_r);
73: if (ksp->its-1 > ksp->chknorm) {
74: (*ksp->converged)(ksp,ksp->its,norm_r,&ksp->reason,ksp->cnvP);
75: if (ksp->reason) break;
76: }
78: if (ksp->its >= ksp->max_it) {
79: ksp->reason = KSP_CONVERGED_ITS;
80: break;
81: }
82: }
83: ctx->n_restarts++;
84: return(0);
85: }
87: static PetscErrorCode KSPSolve_GCR(KSP ksp)
88: {
89: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
91: Mat A, B;
92: Vec r,b,x;
93: PetscReal norm_r = 0.0;
96: KSPGetOperators(ksp, &A, &B);
97: x = ksp->vec_sol;
98: b = ksp->vec_rhs;
99: r = ctx->R;
101: /* compute initial residual */
102: KSP_MatMult(ksp,A, x, r);
103: VecAYPX(r, -1.0, b); /* r = b - A x */
104: if (ksp->normtype != KSP_NORM_NONE) {
105: VecNorm(r, NORM_2, &norm_r);
106: KSPCheckNorm(ksp,norm_r);
107: }
108: ksp->its = 0;
109: ksp->rnorm0 = norm_r;
111: KSPLogResidualHistory(ksp,ksp->rnorm0);
112: KSPMonitor(ksp,ksp->its,ksp->rnorm0);
113: (*ksp->converged)(ksp,ksp->its,ksp->rnorm0,&ksp->reason,ksp->cnvP);
114: if (ksp->reason) return(0);
116: do {
117: KSPSolve_GCR_cycle(ksp);
118: if (ksp->reason) return(0); /* catch case when convergence occurs inside the cycle */
119: } while (ksp->its < ksp->max_it);
121: if (ksp->its >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
122: return(0);
123: }
125: static PetscErrorCode KSPView_GCR(KSP ksp, PetscViewer viewer)
126: {
127: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
129: PetscBool iascii;
132: PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
133: if (iascii) {
134: PetscViewerASCIIPrintf(viewer," restart = %D \n", ctx->restart);
135: PetscViewerASCIIPrintf(viewer," restarts performed = %D \n", ctx->n_restarts);
136: }
137: return(0);
138: }
140: static PetscErrorCode KSPSetUp_GCR(KSP ksp)
141: {
142: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
144: Mat A;
145: PetscBool diagonalscale;
148: PCGetDiagonalScale(ksp->pc,&diagonalscale);
149: if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);
151: KSPGetOperators(ksp, &A, NULL);
152: MatCreateVecs(A, &ctx->R, NULL);
153: VecDuplicateVecs(ctx->R, ctx->restart, &ctx->VV);
154: VecDuplicateVecs(ctx->R, ctx->restart, &ctx->SS);
156: PetscMalloc1(ctx->restart, &ctx->val);
157: return(0);
158: }
160: static PetscErrorCode KSPReset_GCR(KSP ksp)
161: {
163: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
166: VecDestroy(&ctx->R);
167: VecDestroyVecs(ctx->restart,&ctx->VV);
168: VecDestroyVecs(ctx->restart,&ctx->SS);
169: if (ctx->modifypc_destroy) {
170: (*ctx->modifypc_destroy)(ctx->modifypc_ctx);
171: }
172: PetscFree(ctx->val);
173: return(0);
174: }
176: static PetscErrorCode KSPDestroy_GCR(KSP ksp)
177: {
181: KSPReset_GCR(ksp);
182: KSPDestroyDefault(ksp);
183: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRSetRestart_C",NULL);
184: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRGetRestart_C",NULL);
185: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRSetModifyPC_C",NULL);
186: return(0);
187: }
189: static PetscErrorCode KSPSetFromOptions_GCR(PetscOptionItems *PetscOptionsObject,KSP ksp)
190: {
192: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
193: PetscInt restart;
194: PetscBool flg;
197: PetscOptionsHead(PetscOptionsObject,"KSP GCR options");
198: PetscOptionsInt("-ksp_gcr_restart","Number of Krylov search directions","KSPGCRSetRestart",ctx->restart,&restart,&flg);
199: if (flg) { KSPGCRSetRestart(ksp,restart); }
200: PetscOptionsTail();
201: return(0);
202: }
205: typedef PetscErrorCode (*KSPGCRModifyPCFunction)(KSP,PetscInt,PetscReal,void*);
206: typedef PetscErrorCode (*KSPGCRDestroyFunction)(void*);
208: static PetscErrorCode KSPGCRSetModifyPC_GCR(KSP ksp,KSPGCRModifyPCFunction function,void *data,KSPGCRDestroyFunction destroy)
209: {
210: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
214: ctx->modifypc = function;
215: ctx->modifypc_destroy = destroy;
216: ctx->modifypc_ctx = data;
217: return(0);
218: }
220: /*@C
221: KSPGCRSetModifyPC - Sets the routine used by GCR to modify the preconditioner.
223: Logically Collective on ksp
225: Input Parameters:
226: + ksp - iterative context obtained from KSPCreate()
227: . function - user defined function to modify the preconditioner
228: . ctx - user provided context for the modify preconditioner function
229: - destroy - the function to use to destroy the user provided application context.
231: Calling Sequence of function:
232: PetscErrorCode function (KSP ksp, PetscInt n, PetscReal rnorm, void *ctx)
234: ksp - iterative context
235: n - the total number of GCR iterations that have occurred
236: rnorm - 2-norm residual value
237: ctx - the user provided application context
239: Level: intermediate
241: Notes:
242: The default modifypc routine is KSPGCRModifyPCNoChange()
244: .seealso: KSPGCRModifyPCNoChange()
246: @*/
247: PetscErrorCode KSPGCRSetModifyPC(KSP ksp,PetscErrorCode (*function)(KSP,PetscInt,PetscReal,void*),void *data,PetscErrorCode (*destroy)(void*))
248: {
252: PetscUseMethod(ksp,"KSPGCRSetModifyPC_C",(KSP,PetscErrorCode (*)(KSP,PetscInt,PetscReal,void*),void *data,PetscErrorCode (*)(void*)),(ksp,function,data,destroy));
253: return(0);
254: }
256: static PetscErrorCode KSPGCRSetRestart_GCR(KSP ksp,PetscInt restart)
257: {
258: KSP_GCR *ctx;
261: ctx = (KSP_GCR*)ksp->data;
262: ctx->restart = restart;
263: return(0);
264: }
266: static PetscErrorCode KSPGCRGetRestart_GCR(KSP ksp,PetscInt *restart)
267: {
268: KSP_GCR *ctx;
271: ctx = (KSP_GCR*)ksp->data;
272: *restart = ctx->restart;
273: return(0);
274: }
276: /*@
277: KSPGCRSetRestart - Sets number of iterations at which GCR restarts.
279: Not Collective
281: Input Parameters:
282: + ksp - the Krylov space context
283: - restart - integer restart value
285: Note: The default value is 30.
287: Level: intermediate
289: .seealso: KSPSetTolerances(), KSPGCRGetRestart(), KSPGMRESSetRestart()
290: @*/
291: PetscErrorCode KSPGCRSetRestart(KSP ksp, PetscInt restart)
292: {
296: PetscTryMethod(ksp,"KSPGCRSetRestart_C",(KSP,PetscInt),(ksp,restart));
297: return(0);
298: }
300: /*@
301: KSPGCRGetRestart - Gets number of iterations at which GCR restarts.
303: Not Collective
305: Input Parameter:
306: . ksp - the Krylov space context
308: Output Parameter:
309: . restart - integer restart value
311: Note: The default value is 30.
313: Level: intermediate
315: .seealso: KSPSetTolerances(), KSPGCRSetRestart(), KSPGMRESGetRestart()
316: @*/
317: PetscErrorCode KSPGCRGetRestart(KSP ksp, PetscInt *restart)
318: {
322: PetscTryMethod(ksp,"KSPGCRGetRestart_C",(KSP,PetscInt*),(ksp,restart));
323: return(0);
324: }
326: static PetscErrorCode KSPBuildSolution_GCR(KSP ksp, Vec v, Vec *V)
327: {
329: Vec x;
332: x = ksp->vec_sol;
333: if (v) {
334: VecCopy(x, v);
335: if (V) *V = v;
336: } else if (V) {
337: *V = ksp->vec_sol;
338: }
339: return(0);
340: }
342: static PetscErrorCode KSPBuildResidual_GCR(KSP ksp, Vec t, Vec v, Vec *V)
343: {
345: KSP_GCR *ctx;
348: ctx = (KSP_GCR*)ksp->data;
349: if (v) {
350: VecCopy(ctx->R, v);
351: if (V) *V = v;
352: } else if (V) {
353: *V = ctx->R;
354: }
355: return(0);
356: }
358: /*MC
359: KSPGCR - Implements the preconditioned Generalized Conjugate Residual method.
361: Options Database Keys:
362: . -ksp_gcr_restart <restart> - the number of stored vectors to orthogonalize against
364: Level: beginner
366: Notes:
367: The GCR Krylov method supports non-symmetric matrices and permits the use of a preconditioner
368: which may vary from one iteration to the next. Users can can define a method to vary the
369: preconditioner between iterates via KSPGCRSetModifyPC().
371: Restarts are solves with x0 not equal to zero. When a restart occurs, the initial starting
372: solution is given by the current estimate for x which was obtained by the last restart
373: iterations of the GCR algorithm.
375: Unlike GMRES and FGMRES, when using GCR, the solution and residual vector can be directly accessed at any iterate,
376: with zero computational cost, via a call to KSPBuildSolution() and KSPBuildResidual() respectively.
378: This implementation of GCR will only apply the stopping condition test whenever ksp->its > ksp->chknorm,
379: where ksp->chknorm is specified via the command line argument -ksp_check_norm_iteration or via
380: the function KSPSetCheckNormIteration(). Hence the residual norm reported by the monitor and stored
381: in the residual history will be listed as 0.0 before this iteration. It is actually not 0.0; just not calculated.
383: The method implemented requires the storage of 2 x restart + 1 vectors, twice as much as GMRES.
384: Support only for right preconditioning.
386: Contributed by Dave May
388: References:
389: . 1. - S. C. Eisenstat, H. C. Elman, and H. C. Schultz. Variational iterative methods for
390: nonsymmetric systems of linear equations. SIAM J. Numer. Anal., 20, 1983
392: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP,
393: KSPGCRSetRestart(), KSPGCRSetModifyPC(), KSPGMRES, KSPFGMRES
395: M*/
396: PETSC_EXTERN PetscErrorCode KSPCreate_GCR(KSP ksp)
397: {
399: KSP_GCR *ctx;
402: PetscNewLog(ksp,&ctx);
404: ctx->restart = 30;
405: ctx->n_restarts = 0;
406: ksp->data = (void*)ctx;
408: KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);
409: KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,3);
411: ksp->ops->setup = KSPSetUp_GCR;
412: ksp->ops->solve = KSPSolve_GCR;
413: ksp->ops->reset = KSPReset_GCR;
414: ksp->ops->destroy = KSPDestroy_GCR;
415: ksp->ops->view = KSPView_GCR;
416: ksp->ops->setfromoptions = KSPSetFromOptions_GCR;
417: ksp->ops->buildsolution = KSPBuildSolution_GCR;
418: ksp->ops->buildresidual = KSPBuildResidual_GCR;
420: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRSetRestart_C",KSPGCRSetRestart_GCR);
421: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRGetRestart_C",KSPGCRGetRestart_GCR);
422: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRSetModifyPC_C",KSPGCRSetModifyPC_GCR);
423: return(0);
424: }