Actual source code: snesmfj2.c
petsc-3.14.6 2021-03-30
2: #include <petsc/private/snesimpl.h>
3: /* matimpl.h is needed only for logging of matrix operation */
4: #include <petsc/private/matimpl.h>
6: PETSC_INTERN PetscErrorCode SNESUnSetMatrixFreeParameter(SNES);
7: PETSC_INTERN PetscErrorCode SNESDefaultMatrixFreeCreate2(SNES,Vec,Mat*);
8: PETSC_INTERN PetscErrorCode SNESDefaultMatrixFreeSetParameters2(Mat,PetscReal,PetscReal,PetscReal);
10: PETSC_INTERN PetscErrorCode SNESDiffParameterCreate_More(SNES,Vec,void**);
11: PETSC_INTERN PetscErrorCode SNESDiffParameterCompute_More(SNES,void*,Vec,Vec,PetscReal*,PetscReal*);
12: PETSC_INTERN PetscErrorCode SNESDiffParameterDestroy_More(void*);
14: typedef struct { /* default context for matrix-free SNES */
15: SNES snes; /* SNES context */
16: Vec w; /* work vector */
17: MatNullSpace sp; /* null space context */
18: PetscReal error_rel; /* square root of relative error in computing function */
19: PetscReal umin; /* minimum allowable u'a value relative to |u|_1 */
20: PetscBool jorge; /* flag indicating use of Jorge's method for determining the differencing parameter */
21: PetscReal h; /* differencing parameter */
22: PetscBool need_h; /* flag indicating whether we must compute h */
23: PetscBool need_err; /* flag indicating whether we must currently compute error_rel */
24: PetscBool compute_err; /* flag indicating whether we must ever compute error_rel */
25: PetscInt compute_err_iter; /* last iter where we've computer error_rel */
26: PetscInt compute_err_freq; /* frequency of computing error_rel */
27: void *data; /* implementation-specific data */
28: } MFCtx_Private;
30: PetscErrorCode SNESMatrixFreeDestroy2_Private(Mat mat)
31: {
33: MFCtx_Private *ctx;
36: MatShellGetContext(mat,(void**)&ctx);
37: VecDestroy(&ctx->w);
38: MatNullSpaceDestroy(&ctx->sp);
39: if (ctx->jorge || ctx->compute_err) {SNESDiffParameterDestroy_More(ctx->data);}
40: PetscFree(ctx);
41: return(0);
42: }
44: /*
45: SNESMatrixFreeView2_Private - Views matrix-free parameters.
46: */
47: PetscErrorCode SNESMatrixFreeView2_Private(Mat J,PetscViewer viewer)
48: {
50: MFCtx_Private *ctx;
51: PetscBool iascii;
54: MatShellGetContext(J,(void**)&ctx);
55: PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
56: if (iascii) {
57: PetscViewerASCIIPrintf(viewer," SNES matrix-free approximation:\n");
58: if (ctx->jorge) {
59: PetscViewerASCIIPrintf(viewer," using Jorge's method of determining differencing parameter\n");
60: }
61: PetscViewerASCIIPrintf(viewer," err=%g (relative error in function evaluation)\n",(double)ctx->error_rel);
62: PetscViewerASCIIPrintf(viewer," umin=%g (minimum iterate parameter)\n",(double)ctx->umin);
63: if (ctx->compute_err) {
64: PetscViewerASCIIPrintf(viewer," freq_err=%D (frequency for computing err)\n",ctx->compute_err_freq);
65: }
66: }
67: return(0);
68: }
70: /*
71: SNESMatrixFreeMult2_Private - Default matrix-free form for Jacobian-vector
72: product, y = F'(u)*a:
73: y = (F(u + ha) - F(u)) /h,
74: where F = nonlinear function, as set by SNESSetFunction()
75: u = current iterate
76: h = difference interval
77: */
78: PetscErrorCode SNESMatrixFreeMult2_Private(Mat mat,Vec a,Vec y)
79: {
80: MFCtx_Private *ctx;
81: SNES snes;
82: PetscReal h,norm,sum,umin,noise;
83: PetscScalar hs,dot;
84: Vec w,U,F;
85: PetscErrorCode ierr,(*eval_fct)(SNES,Vec,Vec);
86: MPI_Comm comm;
87: PetscInt iter;
90: /* We log matrix-free matrix-vector products separately, so that we can
91: separate the performance monitoring from the cases that use conventional
92: storage. We may eventually modify event logging to associate events
93: with particular objects, hence alleviating the more general problem. */
94: PetscLogEventBegin(MATMFFD_Mult,a,y,0,0);
96: PetscObjectGetComm((PetscObject)mat,&comm);
97: MatShellGetContext(mat,(void**)&ctx);
98: snes = ctx->snes;
99: w = ctx->w;
100: umin = ctx->umin;
102: SNESGetSolution(snes,&U);
103: eval_fct = SNESComputeFunction;
104: SNESGetFunction(snes,&F,NULL,NULL);
106: /* Determine a "good" step size, h */
107: if (ctx->need_h) {
109: /* Use Jorge's method to compute h */
110: if (ctx->jorge) {
111: SNESDiffParameterCompute_More(snes,ctx->data,U,a,&noise,&h);
113: /* Use the Brown/Saad method to compute h */
114: } else {
115: /* Compute error if desired */
116: SNESGetIterationNumber(snes,&iter);
117: if ((ctx->need_err) || ((ctx->compute_err_freq) && (ctx->compute_err_iter != iter) && (!((iter-1)%ctx->compute_err_freq)))) {
118: /* Use Jorge's method to compute noise */
119: SNESDiffParameterCompute_More(snes,ctx->data,U,a,&noise,&h);
121: ctx->error_rel = PetscSqrtReal(noise);
123: PetscInfo3(snes,"Using Jorge's noise: noise=%g, sqrt(noise)=%g, h_more=%g\n",(double)noise,(double)ctx->error_rel,(double)h);
125: ctx->compute_err_iter = iter;
126: ctx->need_err = PETSC_FALSE;
127: }
129: VecDotBegin(U,a,&dot);
130: VecNormBegin(a,NORM_1,&sum);
131: VecNormBegin(a,NORM_2,&norm);
132: VecDotEnd(U,a,&dot);
133: VecNormEnd(a,NORM_1,&sum);
134: VecNormEnd(a,NORM_2,&norm);
137: /* Safeguard for step sizes too small */
138: if (sum == 0.0) {
139: dot = 1.0;
140: norm = 1.0;
141: } else if (PetscAbsScalar(dot) < umin*sum && PetscRealPart(dot) >= 0.0) dot = umin*sum;
142: else if (PetscAbsScalar(dot) < 0.0 && PetscRealPart(dot) > -umin*sum) dot = -umin*sum;
143: h = PetscRealPart(ctx->error_rel*dot/(norm*norm));
144: }
145: } else h = ctx->h;
147: if (!ctx->jorge || !ctx->need_h) {PetscInfo1(snes,"h = %g\n",(double)h);}
149: /* Evaluate function at F(u + ha) */
150: hs = h;
151: VecWAXPY(w,hs,a,U);
152: eval_fct(snes,w,y);
153: VecAXPY(y,-1.0,F);
154: VecScale(y,1.0/hs);
155: if (mat->nullsp) {MatNullSpaceRemove(mat->nullsp,y);}
157: PetscLogEventEnd(MATMFFD_Mult,a,y,0,0);
158: return(0);
159: }
161: /*@C
162: SNESMatrixFreeCreate2 - Creates a matrix-free matrix
163: context for use with a SNES solver. This matrix can be used as
164: the Jacobian argument for the routine SNESSetJacobian().
166: Input Parameters:
167: + snes - the SNES context
168: - x - vector where SNES solution is to be stored.
170: Output Parameter:
171: . J - the matrix-free matrix
173: Level: advanced
175: Notes:
176: The matrix-free matrix context merely contains the function pointers
177: and work space for performing finite difference approximations of
178: Jacobian-vector products, J(u)*a, via
180: $ J(u)*a = [J(u+h*a) - J(u)]/h,
181: $ where by default
182: $ h = error_rel*u'a/||a||^2 if |u'a| > umin*||a||_{1}
183: $ = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2 otherwise
184: $ where
185: $ error_rel = square root of relative error in
186: $ function evaluation
187: $ umin = minimum iterate parameter
188: $ Alternatively, the differencing parameter, h, can be set using
189: $ Jorge's nifty new strategy if one specifies the option
190: $ -snes_mf_jorge
192: The user can set these parameters via MatMFFDSetFunctionError().
193: See Users-Manual: ch_snes for details
195: The user should call MatDestroy() when finished with the matrix-free
196: matrix context.
198: Options Database Keys:
199: $ -snes_mf_err <error_rel>
200: $ -snes_mf_unim <umin>
201: $ -snes_mf_compute_err
202: $ -snes_mf_freq_err <freq>
203: $ -snes_mf_jorge
205: .seealso: MatDestroy(), MatMFFDSetFunctionError()
206: @*/
207: PetscErrorCode SNESDefaultMatrixFreeCreate2(SNES snes,Vec x,Mat *J)
208: {
209: MPI_Comm comm;
210: MFCtx_Private *mfctx;
212: PetscInt n,nloc;
213: PetscBool flg;
214: char p[64];
217: PetscNewLog(snes,&mfctx);
218: mfctx->sp = NULL;
219: mfctx->snes = snes;
220: mfctx->error_rel = PETSC_SQRT_MACHINE_EPSILON;
221: mfctx->umin = 1.e-6;
222: mfctx->h = 0.0;
223: mfctx->need_h = PETSC_TRUE;
224: mfctx->need_err = PETSC_FALSE;
225: mfctx->compute_err = PETSC_FALSE;
226: mfctx->compute_err_freq = 0;
227: mfctx->compute_err_iter = -1;
228: mfctx->compute_err = PETSC_FALSE;
229: mfctx->jorge = PETSC_FALSE;
231: PetscOptionsGetReal(((PetscObject)snes)->options,((PetscObject)snes)->prefix,"-snes_mf_err",&mfctx->error_rel,NULL);
232: PetscOptionsGetReal(((PetscObject)snes)->options,((PetscObject)snes)->prefix,"-snes_mf_umin",&mfctx->umin,NULL);
233: PetscOptionsGetBool(((PetscObject)snes)->options,((PetscObject)snes)->prefix,"-snes_mf_jorge",&mfctx->jorge,NULL);
234: PetscOptionsGetBool(((PetscObject)snes)->options,((PetscObject)snes)->prefix,"-snes_mf_compute_err",&mfctx->compute_err,NULL);
235: PetscOptionsGetInt(((PetscObject)snes)->options,((PetscObject)snes)->prefix,"-snes_mf_freq_err",&mfctx->compute_err_freq,&flg);
236: if (flg) {
237: if (mfctx->compute_err_freq < 0) mfctx->compute_err_freq = 0;
238: mfctx->compute_err = PETSC_TRUE;
239: }
240: if (mfctx->compute_err) mfctx->need_err = PETSC_TRUE;
241: if (mfctx->jorge || mfctx->compute_err) {
242: SNESDiffParameterCreate_More(snes,x,&mfctx->data);
243: } else mfctx->data = NULL;
245: PetscOptionsHasHelp(((PetscObject)snes)->options,&flg);
246: PetscStrncpy(p,"-",sizeof(p));
247: if (((PetscObject)snes)->prefix) {PetscStrlcat(p,((PetscObject)snes)->prefix,sizeof(p));}
248: if (flg) {
249: PetscPrintf(PetscObjectComm((PetscObject)snes)," Matrix-free Options (via SNES):\n");
250: PetscPrintf(PetscObjectComm((PetscObject)snes)," %ssnes_mf_err <err>: set sqrt of relative error in function (default %g)\n",p,(double)mfctx->error_rel);
251: PetscPrintf(PetscObjectComm((PetscObject)snes)," %ssnes_mf_umin <umin>: see users manual (default %g)\n",p,(double)mfctx->umin);
252: PetscPrintf(PetscObjectComm((PetscObject)snes)," %ssnes_mf_jorge: use Jorge More's method\n",p);
253: PetscPrintf(PetscObjectComm((PetscObject)snes)," %ssnes_mf_compute_err: compute sqrt or relative error in function\n",p);
254: PetscPrintf(PetscObjectComm((PetscObject)snes)," %ssnes_mf_freq_err <freq>: frequency to recompute this (default only once)\n",p);
255: PetscPrintf(PetscObjectComm((PetscObject)snes)," %ssnes_mf_noise_file <file>: set file for printing noise info\n",p);
256: }
257: VecDuplicate(x,&mfctx->w);
258: PetscObjectGetComm((PetscObject)x,&comm);
259: VecGetSize(x,&n);
260: VecGetLocalSize(x,&nloc);
261: MatCreate(comm,J);
262: MatSetSizes(*J,nloc,n,n,n);
263: MatSetType(*J,MATSHELL);
264: MatShellSetContext(*J,mfctx);
265: MatShellSetOperation(*J,MATOP_MULT,(void (*)(void))SNESMatrixFreeMult2_Private);
266: MatShellSetOperation(*J,MATOP_DESTROY,(void (*)(void))SNESMatrixFreeDestroy2_Private);
267: MatShellSetOperation(*J,MATOP_VIEW,(void (*)(void))SNESMatrixFreeView2_Private);
268: MatSetUp(*J);
270: PetscLogObjectParent((PetscObject)*J,(PetscObject)mfctx->w);
271: PetscLogObjectParent((PetscObject)snes,(PetscObject)*J);
272: return(0);
273: }
275: /*@C
276: SNESDefaultMatrixFreeSetParameters2 - Sets the parameters for the approximation of
277: matrix-vector products using finite differences.
279: $ J(u)*a = [J(u+h*a) - J(u)]/h where
281: either the user sets h directly here, or this parameter is computed via
283: $ h = error_rel*u'a/||a||^2 if |u'a| > umin*||a||_{1}
284: $ = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2 else
285: $
287: Input Parameters:
288: + mat - the matrix
289: . error_rel - relative error (should be set to the square root of
290: the relative error in the function evaluations)
291: . umin - minimum allowable u-value
292: - h - differencing parameter
294: Level: advanced
296: Notes:
297: If the user sets the parameter h directly, then this value will be used
298: instead of the default computation indicated above.
300: .seealso: MatCreateSNESMF()
301: @*/
302: PetscErrorCode SNESDefaultMatrixFreeSetParameters2(Mat mat,PetscReal error,PetscReal umin,PetscReal h)
303: {
304: MFCtx_Private *ctx;
308: MatShellGetContext(mat,(void**)&ctx);
309: if (ctx) {
310: if (error != PETSC_DEFAULT) ctx->error_rel = error;
311: if (umin != PETSC_DEFAULT) ctx->umin = umin;
312: if (h != PETSC_DEFAULT) {
313: ctx->h = h;
314: ctx->need_h = PETSC_FALSE;
315: }
316: }
317: return(0);
318: }
320: PetscErrorCode SNESUnSetMatrixFreeParameter(SNES snes)
321: {
322: MFCtx_Private *ctx;
324: Mat mat;
327: SNESGetJacobian(snes,&mat,NULL,NULL,NULL);
328: MatShellGetContext(mat,(void**)&ctx);
329: if (ctx) ctx->need_h = PETSC_TRUE;
330: return(0);
331: }