Actual source code: gcr.c
petsc-3.10.5 2019-03-28
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) {
63: VecNorm(r, NORM_2, &norm_r);
64: }
65: /* update the local counter and the global counter */
66: ksp->its++;
67: ksp->rnorm = norm_r;
69: KSPLogResidualHistory(ksp,norm_r);
70: KSPMonitor(ksp,ksp->its,norm_r);
72: if (ksp->its-1 > ksp->chknorm) {
73: (*ksp->converged)(ksp,ksp->its,norm_r,&ksp->reason,ksp->cnvP);
74: if (ksp->reason) break;
75: }
77: if (ksp->its >= ksp->max_it) {
78: ksp->reason = KSP_CONVERGED_ITS;
79: break;
80: }
81: }
82: ctx->n_restarts++;
83: return(0);
84: }
86: static PetscErrorCode KSPSolve_GCR(KSP ksp)
87: {
88: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
90: Mat A, B;
91: Vec r,b,x;
92: PetscReal norm_r;
95: KSPGetOperators(ksp, &A, &B);
96: x = ksp->vec_sol;
97: b = ksp->vec_rhs;
98: r = ctx->R;
100: /* compute initial residual */
101: KSP_MatMult(ksp,A, x, r);
102: VecAYPX(r, -1.0, b); /* r = b - A x */
103: VecNorm(r, NORM_2, &norm_r);
105: ksp->its = 0;
106: ksp->rnorm0 = norm_r;
108: KSPLogResidualHistory(ksp,ksp->rnorm0);
109: KSPMonitor(ksp,ksp->its,ksp->rnorm0);
110: (*ksp->converged)(ksp,ksp->its,ksp->rnorm0,&ksp->reason,ksp->cnvP);
111: if (ksp->reason) return(0);
113: do {
114: KSPSolve_GCR_cycle(ksp);
115: if (ksp->reason) break; /* catch case when convergence occurs inside the cycle */
116: } while (ksp->its < ksp->max_it);
118: if (ksp->its >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
119: return(0);
120: }
122: static PetscErrorCode KSPView_GCR(KSP ksp, PetscViewer viewer)
123: {
124: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
126: PetscBool iascii;
129: PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
130: if (iascii) {
131: PetscViewerASCIIPrintf(viewer," restart = %D \n", ctx->restart);
132: PetscViewerASCIIPrintf(viewer," restarts performed = %D \n", ctx->n_restarts);
133: }
134: return(0);
135: }
138: static PetscErrorCode KSPSetUp_GCR(KSP ksp)
139: {
140: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
142: Mat A;
143: PetscBool diagonalscale;
146: PCGetDiagonalScale(ksp->pc,&diagonalscale);
147: if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);
149: KSPGetOperators(ksp, &A, NULL);
150: MatCreateVecs(A, &ctx->R, NULL);
151: VecDuplicateVecs(ctx->R, ctx->restart, &ctx->VV);
152: VecDuplicateVecs(ctx->R, ctx->restart, &ctx->SS);
154: PetscMalloc1(ctx->restart, &ctx->val);
155: return(0);
156: }
158: static PetscErrorCode KSPReset_GCR(KSP ksp)
159: {
161: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
164: VecDestroy(&ctx->R);
165: VecDestroyVecs(ctx->restart,&ctx->VV);
166: VecDestroyVecs(ctx->restart,&ctx->SS);
167: if (ctx->modifypc_destroy) {
168: (*ctx->modifypc_destroy)(ctx->modifypc_ctx);
169: }
170: PetscFree(ctx->val);
171: return(0);
172: }
174: static PetscErrorCode KSPDestroy_GCR(KSP ksp)
175: {
179: KSPReset_GCR(ksp);
180: KSPDestroyDefault(ksp);
181: return(0);
182: }
184: static PetscErrorCode KSPSetFromOptions_GCR(PetscOptionItems *PetscOptionsObject,KSP ksp)
185: {
187: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
188: PetscInt restart;
189: PetscBool flg;
192: PetscOptionsHead(PetscOptionsObject,"KSP GCR options");
193: PetscOptionsInt("-ksp_gcr_restart","Number of Krylov search directions","KSPGCRSetRestart",ctx->restart,&restart,&flg);
194: if (flg) { KSPGCRSetRestart(ksp,restart); }
195: PetscOptionsTail();
196: return(0);
197: }
200: typedef PetscErrorCode (*KSPGCRModifyPCFunction)(KSP,PetscInt,PetscReal,void*);
201: typedef PetscErrorCode (*KSPGCRDestroyFunction)(void*);
203: static PetscErrorCode KSPGCRSetModifyPC_GCR(KSP ksp,KSPGCRModifyPCFunction function,void *data,KSPGCRDestroyFunction destroy)
204: {
205: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
209: ctx->modifypc = function;
210: ctx->modifypc_destroy = destroy;
211: ctx->modifypc_ctx = data;
212: return(0);
213: }
215: /*@C
216: KSPGCRSetModifyPC - Sets the routine used by GCR to modify the preconditioner.
218: Logically Collective on KSP
220: Input Parameters:
221: + ksp - iterative context obtained from KSPCreate()
222: . function - user defined function to modify the preconditioner
223: . ctx - user provided contex for the modify preconditioner function
224: - destroy - the function to use to destroy the user provided application context.
226: Calling Sequence of function:
227: PetscErrorCode function (KSP ksp, PetscInt n, PetscReal rnorm, void *ctx)
229: ksp - iterative context
230: n - the total number of GCR iterations that have occurred
231: rnorm - 2-norm residual value
232: ctx - the user provided application context
234: Level: intermediate
236: Notes:
237: The default modifypc routine is KSPGCRModifyPCNoChange()
239: .seealso: KSPGCRModifyPCNoChange()
241: @*/
242: PetscErrorCode KSPGCRSetModifyPC(KSP ksp,PetscErrorCode (*function)(KSP,PetscInt,PetscReal,void*),void *data,PetscErrorCode (*destroy)(void*))
243: {
247: PetscUseMethod(ksp,"KSPGCRSetModifyPC_C",(KSP,PetscErrorCode (*)(KSP,PetscInt,PetscReal,void*),void *data,PetscErrorCode (*)(void*)),(ksp,function,data,destroy));
248: return(0);
249: }
251: static PetscErrorCode KSPGCRSetRestart_GCR(KSP ksp,PetscInt restart)
252: {
253: KSP_GCR *ctx;
256: ctx = (KSP_GCR*)ksp->data;
257: ctx->restart = restart;
258: return(0);
259: }
261: PetscErrorCode KSPGCRSetRestart(KSP ksp, PetscInt restart)
262: {
266: PetscTryMethod(ksp,"KSPGCRSetRestart_C",(KSP,PetscInt),(ksp,restart));
267: return(0);
268: }
270: static PetscErrorCode KSPBuildSolution_GCR(KSP ksp, Vec v, Vec *V)
271: {
273: Vec x;
276: x = ksp->vec_sol;
277: if (v) {
278: VecCopy(x, v);
279: if (V) *V = v;
280: } else if (V) {
281: *V = ksp->vec_sol;
282: }
283: return(0);
284: }
286: static PetscErrorCode KSPBuildResidual_GCR(KSP ksp, Vec t, Vec v, Vec *V)
287: {
289: KSP_GCR *ctx;
292: ctx = (KSP_GCR*)ksp->data;
293: if (v) {
294: VecCopy(ctx->R, v);
295: if (V) *V = v;
296: } else if (V) {
297: *V = ctx->R;
298: }
299: return(0);
300: }
302: /*MC
303: KSPGCR - Implements the preconditioned Generalized Conjugate Residual method.
305: Options Database Keys:
306: . -ksp_gcr_restart <restart> - the number of stored vectors to orthogonalize against
308: Level: beginner
310: Notes:
311: The GCR Krylov method supports non-symmetric matrices and permits the use of a preconditioner
312: which may vary from one iteration to the next. Users can can define a method to vary the
313: preconditioner between iterates via KSPGCRSetModifyPC().
315: Restarts are solves with x0 not equal to zero. When a restart occurs, the initial starting
316: solution is given by the current estimate for x which was obtained by the last restart
317: iterations of the GCR algorithm.
319: Unlike GMRES and FGMRES, when using GCR, the solution and residual vector can be directly accessed at any iterate,
320: with zero computational cost, via a call to KSPBuildSolution() and KSPBuildResidual() respectively.
322: This implementation of GCR will only apply the stopping condition test whenever ksp->its > ksp->chknorm,
323: where ksp->chknorm is specified via the command line argument -ksp_check_norm_iteration or via
324: the function KSPSetCheckNormIteration(). Hence the residual norm reported by the monitor and stored
325: in the residual history will be listed as 0.0 before this iteration. It is actually not 0.0; just not calculated.
327: The method implemented requires the storage of 2 x restart + 1 vectors, twice as much as GMRES.
328: Support only for right preconditioning.
330: Contributed by Dave May
332: References:
333: . 1. - S. C. Eisenstat, H. C. Elman, and H. C. Schultz. Variational iterative methods for
334: nonsymmetric systems of linear equations. SIAM J. Numer. Anal., 20, 1983
337: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP,
338: KSPGCRSetRestart(), KSPGCRSetModifyPC(), KSPGMRES, KSPFGMRES
340: M*/
341: PETSC_EXTERN PetscErrorCode KSPCreate_GCR(KSP ksp)
342: {
344: KSP_GCR *ctx;
347: PetscNewLog(ksp,&ctx);
349: ctx->restart = 30;
350: ctx->n_restarts = 0;
351: ksp->data = (void*)ctx;
353: KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,3);
355: ksp->ops->setup = KSPSetUp_GCR;
356: ksp->ops->solve = KSPSolve_GCR;
357: ksp->ops->reset = KSPReset_GCR;
358: ksp->ops->destroy = KSPDestroy_GCR;
359: ksp->ops->view = KSPView_GCR;
360: ksp->ops->setfromoptions = KSPSetFromOptions_GCR;
361: ksp->ops->buildsolution = KSPBuildSolution_GCR;
362: ksp->ops->buildresidual = KSPBuildResidual_GCR;
364: PetscObjectComposeFunction((PetscObject)ksp, "KSPGCRSetRestart_C",KSPGCRSetRestart_GCR);
365: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRSetModifyPC_C",KSPGCRSetModifyPC_GCR);
366: return(0);
367: }