Actual source code: linesearchbt.c
1: #include <petsc/private/linesearchimpl.h>
2: #include <petsc/private/snesimpl.h>
4: typedef struct {
5: PetscReal alpha; /* sufficient decrease parameter */
6: } SNESLineSearch_BT;
8: /*@
9: SNESLineSearchBTSetAlpha - Sets the descent parameter, `alpha`, in the `SNESLINESEARCHBT` `SNESLineSearch` variant.
11: Input Parameters:
12: + linesearch - linesearch context
13: - alpha - The descent parameter
15: Level: intermediate
17: .seealso: [](ch_snes), `SNESLineSearch`, `SNESLineSearchSetLambda()`, `SNESLineSearchGetTolerances()`, `SNESLINESEARCHBT`, `SNESLineSearchBTGetAlpha()`
18: @*/
19: PetscErrorCode SNESLineSearchBTSetAlpha(SNESLineSearch linesearch, PetscReal alpha)
20: {
21: SNESLineSearch_BT *bt = (SNESLineSearch_BT *)linesearch->data;
22: PetscBool isbt;
24: PetscFunctionBegin;
26: PetscCall(PetscObjectTypeCompare((PetscObject)linesearch, SNESLINESEARCHBT, &isbt));
27: if (isbt) bt->alpha = alpha;
28: PetscFunctionReturn(PETSC_SUCCESS);
29: }
31: /*@
32: SNESLineSearchBTGetAlpha - Gets the descent parameter, `alpha`, in the `SNESLINESEARCHBT` variant that was set with `SNESLineSearchBTSetAlpha()`
34: Input Parameter:
35: . linesearch - linesearch context
37: Output Parameter:
38: . alpha - The descent parameter
40: Level: intermediate
42: .seealso: [](ch_snes), `SNESLineSearch`, `SNESLineSearchGetLambda()`, `SNESLineSearchGetTolerances()`, `SNESLINESEARCHBT`, `SNESLineSearchBTSetAlpha()`
43: @*/
44: PetscErrorCode SNESLineSearchBTGetAlpha(SNESLineSearch linesearch, PetscReal *alpha)
45: {
46: SNESLineSearch_BT *bt = (SNESLineSearch_BT *)linesearch->data;
47: PetscBool isbt;
49: PetscFunctionBegin;
51: PetscCall(PetscObjectTypeCompare((PetscObject)linesearch, SNESLINESEARCHBT, &isbt));
52: PetscCheck(isbt, PetscObjectComm((PetscObject)linesearch), PETSC_ERR_USER, "Not for type %s", ((PetscObject)linesearch)->type_name);
53: *alpha = bt->alpha;
54: PetscFunctionReturn(PETSC_SUCCESS);
55: }
57: static PetscErrorCode SNESLineSearchApply_BT(SNESLineSearch linesearch)
58: {
59: SNESLineSearch_BT *bt = (SNESLineSearch_BT *)linesearch->data;
60: PetscBool changed_y, changed_w;
61: Vec X, F, Y, W, G;
62: SNES snes;
63: PetscReal fnorm, xnorm, ynorm, gnorm;
64: PetscReal lambda, lambdatemp, lambdaprev, minlambda, initslope, alpha, stol;
65: PetscReal t1, t2, a, b, d;
66: PetscReal f;
67: PetscReal g, gprev;
68: PetscViewer monitor;
69: PetscInt max_it, count;
70: Mat jac;
71: SNESObjectiveFn *objective;
72: const char *const ordStr[] = {"Linear", "Quadratic", "Cubic"};
74: PetscFunctionBegin;
75: PetscCall(SNESLineSearchGetVecs(linesearch, &X, &F, &Y, &W, &G));
76: PetscCall(SNESLineSearchGetNorms(linesearch, NULL, &fnorm, NULL));
77: PetscCall(SNESLineSearchGetLambda(linesearch, &lambda));
78: PetscCall(SNESLineSearchGetSNES(linesearch, &snes));
79: PetscCall(SNESLineSearchGetDefaultMonitor(linesearch, &monitor));
80: PetscCall(SNESLineSearchGetTolerances(linesearch, &minlambda, NULL, NULL, NULL, NULL, &max_it));
81: PetscCall(SNESGetTolerances(snes, NULL, NULL, &stol, NULL, NULL));
82: PetscCall(SNESGetObjective(snes, &objective, NULL));
83: alpha = bt->alpha;
85: PetscCall(SNESGetJacobian(snes, &jac, NULL, NULL, NULL));
86: PetscCheck(jac || objective, PetscObjectComm((PetscObject)linesearch), PETSC_ERR_USER, "SNESLineSearchBT requires a Jacobian matrix");
88: PetscCall(SNESLineSearchPreCheck(linesearch, X, Y, &changed_y));
89: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_SUCCEEDED));
91: PetscCall(VecNormBegin(Y, NORM_2, &ynorm));
92: PetscCall(VecNormBegin(X, NORM_2, &xnorm));
93: PetscCall(VecNormEnd(Y, NORM_2, &ynorm));
94: PetscCall(VecNormEnd(X, NORM_2, &xnorm));
96: if (ynorm == 0.0) {
97: if (monitor) {
98: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
99: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Initial direction and size is 0\n"));
100: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
101: }
102: PetscCall(VecCopy(X, W));
103: PetscCall(VecCopy(F, G));
104: PetscCall(SNESLineSearchSetNorms(linesearch, xnorm, fnorm, ynorm));
105: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_REDUCT));
106: PetscFunctionReturn(PETSC_SUCCESS);
107: }
109: /* if the SNES has an objective set, use that instead of the function value */
110: if (objective) {
111: PetscCall(SNESComputeObjective(snes, X, &f));
112: SNESLineSearchCheckObjectiveDomainError(snes, f);
113: } else {
114: f = 0.5 * PetscSqr(fnorm);
115: }
117: /* compute the initial slope */
118: if (objective) {
119: /* slope comes from the function (assumed to be the gradient of the objective) */
120: PetscCall(VecDotRealPart(Y, F, &initslope));
121: } else {
122: /* slope comes from the normal equations */
123: PetscCall(MatMult(jac, Y, W));
124: PetscCall(VecDotRealPart(F, W, &initslope));
125: if (initslope > 0.0) initslope = -initslope;
126: if (initslope == 0.0) initslope = -1.0;
127: }
129: /* repeatedly cut lambda until the norm or objective function is not infinity or NaN or lambda is too small */
130: while (PETSC_TRUE) {
131: PetscCall(VecWAXPY(W, -lambda, Y, X));
132: if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W));
133: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
134: PetscCall(PetscInfo(snes, "Exceeded maximum function evaluations, while checking full step length!\n"));
135: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
136: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_FUNCTION));
137: PetscFunctionReturn(PETSC_SUCCESS);
138: }
140: if (objective) {
141: PetscCall(SNESComputeObjective(snes, W, &g));
142: } else {
143: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
144: if (linesearch->ops->vinorm) {
145: gnorm = fnorm;
146: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
147: } else {
148: PetscCall(VecNorm(G, NORM_2, &gnorm));
149: }
150: g = 0.5 * PetscSqr(gnorm);
151: }
152: PetscCall(SNESLineSearchMonitor(linesearch));
154: if (!PetscIsInfOrNanReal(g)) break;
155: if (monitor) {
156: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
157: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: objective function at lambdas = %g is infinity or NaN, cutting lambda\n", (double)lambda));
158: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
159: }
160: if (lambda <= minlambda) SNESCheckFunctionDomainError(snes, g);
161: lambda *= .5;
162: }
164: if (!objective) PetscCall(PetscInfo(snes, "Initial fnorm %14.12e gnorm %14.12e\n", (double)fnorm, (double)gnorm));
165: if (g <= f + lambda * alpha * initslope) { /* Sufficient reduction or step tolerance convergence */
166: if (monitor) {
167: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
168: if (!objective) {
169: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Using full step: fnorm %14.12e gnorm %14.12e\n", (double)fnorm, (double)gnorm));
170: } else {
171: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Using full step: old obj %14.12e new obj %14.12e\n", (double)f, (double)g));
172: }
173: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
174: }
175: } else {
176: if (stol * xnorm > ynorm) {
177: /* Since the full step didn't give sufficient decrease and the step is tiny, exit */
178: PetscCall(SNESLineSearchSetNorms(linesearch, xnorm, fnorm, ynorm));
179: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_SUCCEEDED));
180: if (monitor) {
181: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
182: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Ended due to ynorm < stol*xnorm (%14.12e < %14.12e).\n", (double)ynorm, (double)(stol * xnorm)));
183: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
184: }
185: PetscFunctionReturn(PETSC_SUCCESS);
186: }
187: /* Here to avoid -Wmaybe-uninitiliazed warnings */
188: lambdaprev = lambda;
189: gprev = g;
190: if (linesearch->order != SNES_LINESEARCH_ORDER_LINEAR) {
191: /* Fit points with quadratic */
192: lambdatemp = -initslope * PetscSqr(lambda) / (2.0 * (g - f - lambda * initslope));
193: lambda = PetscClipInterval(lambdatemp, .1 * lambda, .5 * lambda);
195: PetscCall(VecWAXPY(W, -lambda, Y, X));
196: if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W));
197: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
198: PetscCall(PetscInfo(snes, "Exceeded maximum function evaluations, while attempting quadratic backtracking! %" PetscInt_FMT " \n", snes->nfuncs));
199: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
200: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_FUNCTION));
201: PetscFunctionReturn(PETSC_SUCCESS);
202: }
203: if (objective) {
204: PetscCall(SNESComputeObjective(snes, W, &g));
205: SNESLineSearchCheckObjectiveDomainError(snes, g);
206: } else {
207: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
208: if (linesearch->ops->vinorm) {
209: gnorm = fnorm;
210: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
211: } else {
212: PetscCall(VecNorm(G, NORM_2, &gnorm));
213: }
214: SNESLineSearchCheckFunctionDomainError(snes, linesearch, gnorm);
215: g = 0.5 * PetscSqr(gnorm);
216: }
217: if (PetscIsInfOrNanReal(g)) {
218: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_NANORINF));
219: PetscCall(PetscInfo(snes, "Aborted due to infinity or NaN in function evaluation\n"));
220: PetscFunctionReturn(PETSC_SUCCESS);
221: }
222: if (monitor) {
223: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
224: if (!objective) {
225: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: gnorm after quadratic fit %14.12e\n", (double)gnorm));
226: } else {
227: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: obj after quadratic fit %14.12e\n", (double)g));
228: }
229: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
230: }
231: }
232: if (linesearch->order != SNES_LINESEARCH_ORDER_LINEAR && g <= f + lambda * alpha * initslope) { /* sufficient reduction */
233: if (monitor) {
234: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
235: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Quadratically determined step, lambda=%18.16e\n", (double)lambda));
236: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
237: }
238: } else {
239: for (count = 0; count < max_it; count++) {
240: if (lambda <= minlambda) {
241: if (monitor) {
242: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
243: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: unable to find good step length! After %" PetscInt_FMT " tries \n", count));
244: if (!objective) {
245: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: fnorm=%18.16e, gnorm=%18.16e, ynorm=%18.16e, minlambda=%18.16e, lambda=%18.16e, initial slope=%18.16e\n", (double)fnorm, (double)gnorm, (double)ynorm, (double)minlambda, (double)lambda, (double)initslope));
246: } else {
247: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: obj(0)=%18.16e, obj=%18.16e, ynorm=%18.16e, minlambda=%18.16e, lambda=%18.16e, initial slope=%18.16e\n", (double)f, (double)g, (double)ynorm, (double)minlambda, (double)lambda, (double)initslope));
248: }
249: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
250: }
251: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_REDUCT));
252: PetscFunctionReturn(PETSC_SUCCESS);
253: }
254: if (linesearch->order == SNES_LINESEARCH_ORDER_CUBIC) {
255: /* Fit points with cubic */
256: t1 = g - f - lambda * initslope;
257: t2 = gprev - f - lambdaprev * initslope;
258: a = (t1 / (lambda * lambda) - t2 / (lambdaprev * lambdaprev)) / (lambda - lambdaprev);
259: b = (-lambdaprev * t1 / (lambda * lambda) + lambda * t2 / (lambdaprev * lambdaprev)) / (lambda - lambdaprev);
260: d = b * b - 3 * a * initslope;
261: if (d < 0.0) d = 0.0;
262: if (a == 0.0) lambdatemp = -initslope / (2.0 * b);
263: else lambdatemp = (-b + PetscSqrtReal(d)) / (3.0 * a);
264: } else if (linesearch->order == SNES_LINESEARCH_ORDER_QUADRATIC) {
265: lambdatemp = -initslope * PetscSqr(lambda) / (2.0 * (g - f - lambda * initslope));
266: } else if (linesearch->order == SNES_LINESEARCH_ORDER_LINEAR) { /* Just backtrack */
267: lambdatemp = .5 * lambda;
268: } else SETERRQ(PetscObjectComm((PetscObject)linesearch), PETSC_ERR_SUP, "Line search order %" PetscInt_FMT " for type bt", linesearch->order);
269: lambdaprev = lambda;
270: gprev = g;
272: lambda = PetscClipInterval(lambdatemp, .1 * lambda, .5 * lambda);
273: PetscCall(VecWAXPY(W, -lambda, Y, X));
274: if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W));
275: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
276: PetscCall(PetscInfo(snes, "Exceeded maximum function evaluations, while looking for good step length! %" PetscInt_FMT " \n", count));
277: if (!objective) PetscCall(PetscInfo(snes, "fnorm=%18.16e, gnorm=%18.16e, ynorm=%18.16e, lambda=%18.16e, initial slope=%18.16e\n", (double)fnorm, (double)gnorm, (double)ynorm, (double)lambda, (double)initslope));
278: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_FUNCTION));
279: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
280: PetscFunctionReturn(PETSC_SUCCESS);
281: }
282: if (objective) {
283: PetscCall(SNESComputeObjective(snes, W, &g));
284: SNESLineSearchCheckObjectiveDomainError(snes, g);
285: } else {
286: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
287: if (linesearch->ops->vinorm) {
288: gnorm = fnorm;
289: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
290: } else {
291: PetscCall(VecNorm(G, NORM_2, &gnorm));
292: }
293: SNESLineSearchCheckFunctionDomainError(snes, linesearch, gnorm);
294: g = 0.5 * PetscSqr(gnorm);
295: }
296: if (g <= f + lambda * alpha * initslope) { /* is reduction enough? */
297: if (monitor) {
298: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
299: if (!objective) {
300: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: %s step, current gnorm %14.12e lambda=%18.16e\n", ordStr[linesearch->order - 1], (double)gnorm, (double)lambda));
301: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
302: } else {
303: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: %s step, obj %14.12e lambda=%18.16e\n", ordStr[linesearch->order - 1], (double)g, (double)lambda));
304: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
305: }
306: }
307: break;
308: } else if (monitor) {
309: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
310: if (!objective) {
311: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: %s step no good, shrinking lambda, current gnorm %12.12e lambda=%18.16e\n", ordStr[linesearch->order - 1], (double)gnorm, (double)lambda));
312: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
313: } else {
314: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: %s step no good, shrinking lambda, obj %12.12e lambda=%18.16e\n", ordStr[linesearch->order - 1], (double)g, (double)lambda));
315: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
316: }
317: }
318: }
319: }
320: }
322: /* postcheck */
323: PetscCall(SNESLineSearchSetLambda(linesearch, lambda));
324: PetscCall(SNESLineSearchPostCheck(linesearch, X, Y, W, &changed_y, &changed_w));
325: if (changed_y) {
326: if (!changed_w) PetscCall(VecWAXPY(W, -lambda, Y, X));
327: if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W));
328: }
329: if (changed_y || changed_w || objective) { /* recompute the function norm if the step has changed or the objective isn't the norm */
330: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
331: if (linesearch->ops->vinorm) {
332: gnorm = fnorm;
333: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
334: } else {
335: PetscCall(VecNorm(G, NORM_2, &gnorm));
336: }
337: SNESLineSearchCheckFunctionDomainError(snes, linesearch, gnorm);
338: PetscCall(VecNorm(Y, NORM_2, &ynorm));
339: }
341: /* copy the solution over */
342: PetscCall(VecCopy(W, X));
343: PetscCall(VecCopy(G, F));
344: PetscCall(VecNorm(X, NORM_2, &xnorm));
345: PetscCall(SNESLineSearchSetNorms(linesearch, xnorm, gnorm, ynorm));
346: PetscFunctionReturn(PETSC_SUCCESS);
347: }
349: static PetscErrorCode SNESLineSearchView_BT(SNESLineSearch linesearch, PetscViewer viewer)
350: {
351: PetscBool isascii;
352: SNESLineSearch_BT *bt = (SNESLineSearch_BT *)linesearch->data;
354: PetscFunctionBegin;
355: PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
356: if (isascii) {
357: if (linesearch->order == SNES_LINESEARCH_ORDER_CUBIC) {
358: PetscCall(PetscViewerASCIIPrintf(viewer, " interpolation: cubic\n"));
359: } else if (linesearch->order == SNES_LINESEARCH_ORDER_QUADRATIC) {
360: PetscCall(PetscViewerASCIIPrintf(viewer, " interpolation: quadratic\n"));
361: }
362: PetscCall(PetscViewerASCIIPrintf(viewer, " alpha=%e\n", (double)bt->alpha));
363: }
364: PetscFunctionReturn(PETSC_SUCCESS);
365: }
367: static PetscErrorCode SNESLineSearchDestroy_BT(SNESLineSearch linesearch)
368: {
369: PetscFunctionBegin;
370: PetscCall(PetscFree(linesearch->data));
371: PetscFunctionReturn(PETSC_SUCCESS);
372: }
374: static PetscErrorCode SNESLineSearchSetFromOptions_BT(SNESLineSearch linesearch, PetscOptionItems PetscOptionsObject)
375: {
376: SNESLineSearch_BT *bt = (SNESLineSearch_BT *)linesearch->data;
378: PetscFunctionBegin;
379: PetscOptionsHeadBegin(PetscOptionsObject, "SNESLineSearch BT options");
380: PetscCall(PetscOptionsReal("-snes_linesearch_alpha", "Descent tolerance", "SNESLineSearchBT", bt->alpha, &bt->alpha, NULL));
381: PetscOptionsHeadEnd();
382: PetscFunctionReturn(PETSC_SUCCESS);
383: }
385: /*MC
386: SNESLINESEARCHBT - Backtracking line search {cite}`dennis:83`.
388: This line search finds the minimum of a polynomial fitting either $1/2 ||F(x_k + \lambda Y_k)||_2^2$,
389: or the objective function $G(x_k + \lambda Y_k)$ if it is provided with `SNESSetObjective()`.
390: If this fit does not satisfy the sufficient decrease conditions, the interval shrinks
391: and the fit is reattempted at most `max_it` times or until $\lambda$ is below `minlambda`.
393: Options Database Keys:
394: + -snes_linesearch_alpha <1e\-4> - slope descent parameter
395: . -snes_linesearch_damping <1.0> - initial `lambda` on entry to the line search
396: . -snes_linesearch_max_it <40> - maximum number of shrinking iterations in the line search
397: . -snes_linesearch_minlambda <1e\-12> - minimum `lambda` (scaling of solution update) allowed
398: - -snes_linesearch_order <3> - order of the polynomial fit, must be 1, 2, or 3. With order 1, it performs a simple backtracking without any curve fitting
400: Level: advanced
402: Note:
403: This line search will always produce a step that is less than or equal to, in length, the full step size.
405: .seealso: [](ch_snes), `SNESLineSearch`, `SNESLineSearchType`, `SNESLineSearchCreate()`, `SNESLineSearchSetType()`
406: M*/
407: PETSC_EXTERN PetscErrorCode SNESLineSearchCreate_BT(SNESLineSearch linesearch)
408: {
409: SNESLineSearch_BT *bt;
411: PetscFunctionBegin;
412: linesearch->ops->apply = SNESLineSearchApply_BT;
413: linesearch->ops->destroy = SNESLineSearchDestroy_BT;
414: linesearch->ops->setfromoptions = SNESLineSearchSetFromOptions_BT;
415: linesearch->ops->reset = NULL;
416: linesearch->ops->view = SNESLineSearchView_BT;
417: linesearch->ops->setup = NULL;
419: PetscCall(PetscNew(&bt));
421: linesearch->data = (void *)bt;
422: linesearch->max_it = 40;
423: linesearch->order = SNES_LINESEARCH_ORDER_CUBIC;
424: bt->alpha = 1e-4;
425: PetscFunctionReturn(PETSC_SUCCESS);
426: }