Actual source code: gcr.c
petsc-3.11.4 2019-09-28
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: 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;
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: VecNorm(r, NORM_2, &norm_r);
105: KSPCheckNorm(ksp,norm_r);
106: ksp->its = 0;
107: ksp->rnorm0 = norm_r;
109: KSPLogResidualHistory(ksp,ksp->rnorm0);
110: KSPMonitor(ksp,ksp->its,ksp->rnorm0);
111: (*ksp->converged)(ksp,ksp->its,ksp->rnorm0,&ksp->reason,ksp->cnvP);
112: if (ksp->reason) return(0);
114: do {
115: KSPSolve_GCR_cycle(ksp);
116: if (ksp->reason) break; /* catch case when convergence occurs inside the cycle */
117: } while (ksp->its < ksp->max_it);
119: if (ksp->its >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
120: return(0);
121: }
123: static PetscErrorCode KSPView_GCR(KSP ksp, PetscViewer viewer)
124: {
125: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
127: PetscBool iascii;
130: PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
131: if (iascii) {
132: PetscViewerASCIIPrintf(viewer," restart = %D \n", ctx->restart);
133: PetscViewerASCIIPrintf(viewer," restarts performed = %D \n", ctx->n_restarts);
134: }
135: return(0);
136: }
139: static PetscErrorCode KSPSetUp_GCR(KSP ksp)
140: {
141: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
143: Mat A;
144: PetscBool diagonalscale;
147: PCGetDiagonalScale(ksp->pc,&diagonalscale);
148: if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);
150: KSPGetOperators(ksp, &A, NULL);
151: MatCreateVecs(A, &ctx->R, NULL);
152: VecDuplicateVecs(ctx->R, ctx->restart, &ctx->VV);
153: VecDuplicateVecs(ctx->R, ctx->restart, &ctx->SS);
155: PetscMalloc1(ctx->restart, &ctx->val);
156: return(0);
157: }
159: static PetscErrorCode KSPReset_GCR(KSP ksp)
160: {
162: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
165: VecDestroy(&ctx->R);
166: VecDestroyVecs(ctx->restart,&ctx->VV);
167: VecDestroyVecs(ctx->restart,&ctx->SS);
168: if (ctx->modifypc_destroy) {
169: (*ctx->modifypc_destroy)(ctx->modifypc_ctx);
170: }
171: PetscFree(ctx->val);
172: return(0);
173: }
175: static PetscErrorCode KSPDestroy_GCR(KSP ksp)
176: {
180: KSPReset_GCR(ksp);
181: KSPDestroyDefault(ksp);
182: return(0);
183: }
185: static PetscErrorCode KSPSetFromOptions_GCR(PetscOptionItems *PetscOptionsObject,KSP ksp)
186: {
188: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
189: PetscInt restart;
190: PetscBool flg;
193: PetscOptionsHead(PetscOptionsObject,"KSP GCR options");
194: PetscOptionsInt("-ksp_gcr_restart","Number of Krylov search directions","KSPGCRSetRestart",ctx->restart,&restart,&flg);
195: if (flg) { KSPGCRSetRestart(ksp,restart); }
196: PetscOptionsTail();
197: return(0);
198: }
201: typedef PetscErrorCode (*KSPGCRModifyPCFunction)(KSP,PetscInt,PetscReal,void*);
202: typedef PetscErrorCode (*KSPGCRDestroyFunction)(void*);
204: static PetscErrorCode KSPGCRSetModifyPC_GCR(KSP ksp,KSPGCRModifyPCFunction function,void *data,KSPGCRDestroyFunction destroy)
205: {
206: KSP_GCR *ctx = (KSP_GCR*)ksp->data;
210: ctx->modifypc = function;
211: ctx->modifypc_destroy = destroy;
212: ctx->modifypc_ctx = data;
213: return(0);
214: }
216: /*@C
217: KSPGCRSetModifyPC - Sets the routine used by GCR to modify the preconditioner.
219: Logically Collective on KSP
221: Input Parameters:
222: + ksp - iterative context obtained from KSPCreate()
223: . function - user defined function to modify the preconditioner
224: . ctx - user provided contex for the modify preconditioner function
225: - destroy - the function to use to destroy the user provided application context.
227: Calling Sequence of function:
228: PetscErrorCode function (KSP ksp, PetscInt n, PetscReal rnorm, void *ctx)
230: ksp - iterative context
231: n - the total number of GCR iterations that have occurred
232: rnorm - 2-norm residual value
233: ctx - the user provided application context
235: Level: intermediate
237: Notes:
238: The default modifypc routine is KSPGCRModifyPCNoChange()
240: .seealso: KSPGCRModifyPCNoChange()
242: @*/
243: PetscErrorCode KSPGCRSetModifyPC(KSP ksp,PetscErrorCode (*function)(KSP,PetscInt,PetscReal,void*),void *data,PetscErrorCode (*destroy)(void*))
244: {
248: PetscUseMethod(ksp,"KSPGCRSetModifyPC_C",(KSP,PetscErrorCode (*)(KSP,PetscInt,PetscReal,void*),void *data,PetscErrorCode (*)(void*)),(ksp,function,data,destroy));
249: return(0);
250: }
252: static PetscErrorCode KSPGCRSetRestart_GCR(KSP ksp,PetscInt restart)
253: {
254: KSP_GCR *ctx;
257: ctx = (KSP_GCR*)ksp->data;
258: ctx->restart = restart;
259: return(0);
260: }
262: PetscErrorCode KSPGCRSetRestart(KSP ksp, PetscInt restart)
263: {
267: PetscTryMethod(ksp,"KSPGCRSetRestart_C",(KSP,PetscInt),(ksp,restart));
268: return(0);
269: }
271: static PetscErrorCode KSPBuildSolution_GCR(KSP ksp, Vec v, Vec *V)
272: {
274: Vec x;
277: x = ksp->vec_sol;
278: if (v) {
279: VecCopy(x, v);
280: if (V) *V = v;
281: } else if (V) {
282: *V = ksp->vec_sol;
283: }
284: return(0);
285: }
287: static PetscErrorCode KSPBuildResidual_GCR(KSP ksp, Vec t, Vec v, Vec *V)
288: {
290: KSP_GCR *ctx;
293: ctx = (KSP_GCR*)ksp->data;
294: if (v) {
295: VecCopy(ctx->R, v);
296: if (V) *V = v;
297: } else if (V) {
298: *V = ctx->R;
299: }
300: return(0);
301: }
303: /*MC
304: KSPGCR - Implements the preconditioned Generalized Conjugate Residual method.
306: Options Database Keys:
307: . -ksp_gcr_restart <restart> - the number of stored vectors to orthogonalize against
309: Level: beginner
311: Notes:
312: The GCR Krylov method supports non-symmetric matrices and permits the use of a preconditioner
313: which may vary from one iteration to the next. Users can can define a method to vary the
314: preconditioner between iterates via KSPGCRSetModifyPC().
316: Restarts are solves with x0 not equal to zero. When a restart occurs, the initial starting
317: solution is given by the current estimate for x which was obtained by the last restart
318: iterations of the GCR algorithm.
320: Unlike GMRES and FGMRES, when using GCR, the solution and residual vector can be directly accessed at any iterate,
321: with zero computational cost, via a call to KSPBuildSolution() and KSPBuildResidual() respectively.
323: This implementation of GCR will only apply the stopping condition test whenever ksp->its > ksp->chknorm,
324: where ksp->chknorm is specified via the command line argument -ksp_check_norm_iteration or via
325: the function KSPSetCheckNormIteration(). Hence the residual norm reported by the monitor and stored
326: in the residual history will be listed as 0.0 before this iteration. It is actually not 0.0; just not calculated.
328: The method implemented requires the storage of 2 x restart + 1 vectors, twice as much as GMRES.
329: Support only for right preconditioning.
331: Contributed by Dave May
333: References:
334: . 1. - S. C. Eisenstat, H. C. Elman, and H. C. Schultz. Variational iterative methods for
335: nonsymmetric systems of linear equations. SIAM J. Numer. Anal., 20, 1983
338: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP,
339: KSPGCRSetRestart(), KSPGCRSetModifyPC(), KSPGMRES, KSPFGMRES
341: M*/
342: PETSC_EXTERN PetscErrorCode KSPCreate_GCR(KSP ksp)
343: {
345: KSP_GCR *ctx;
348: PetscNewLog(ksp,&ctx);
350: ctx->restart = 30;
351: ctx->n_restarts = 0;
352: ksp->data = (void*)ctx;
354: KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,3);
356: ksp->ops->setup = KSPSetUp_GCR;
357: ksp->ops->solve = KSPSolve_GCR;
358: ksp->ops->reset = KSPReset_GCR;
359: ksp->ops->destroy = KSPDestroy_GCR;
360: ksp->ops->view = KSPView_GCR;
361: ksp->ops->setfromoptions = KSPSetFromOptions_GCR;
362: ksp->ops->buildsolution = KSPBuildSolution_GCR;
363: ksp->ops->buildresidual = KSPBuildResidual_GCR;
365: PetscObjectComposeFunction((PetscObject)ksp, "KSPGCRSetRestart_C",KSPGCRSetRestart_GCR);
366: PetscObjectComposeFunction((PetscObject)ksp,"KSPGCRSetModifyPC_C",KSPGCRSetModifyPC_GCR);
367: return(0);
368: }