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) PetscCall(SNESComputeObjective(snes, W, &g));
141: else {
142: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
143: if (linesearch->ops->vinorm) {
144: gnorm = fnorm;
145: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
146: } else {
147: PetscCall(VecNorm(G, NORM_2, &gnorm));
148: }
149: g = 0.5 * PetscSqr(gnorm);
150: }
151: PetscCall(SNESLineSearchMonitor(linesearch));
153: if (!PetscIsInfOrNanReal(g)) break;
154: if (monitor) {
155: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
156: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: objective function at lambdas = %g is infinity or NaN, cutting lambda\n", (double)lambda));
157: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
158: }
159: if (lambda <= minlambda) SNESCheckFunctionDomainError(snes, g);
160: lambda *= .5;
161: }
163: if (!objective) PetscCall(PetscInfo(snes, "Initial fnorm %14.12e gnorm %14.12e\n", (double)fnorm, (double)gnorm));
164: if (g <= f + lambda * alpha * initslope) { /* Sufficient reduction or step tolerance convergence */
165: if (monitor) {
166: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
167: if (!objective) {
168: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Using full step: fnorm %14.12e gnorm %14.12e\n", (double)fnorm, (double)gnorm));
169: } else {
170: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Using full step: old obj %14.12e new obj %14.12e\n", (double)f, (double)g));
171: }
172: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
173: }
174: } else {
175: if (stol * xnorm > ynorm) {
176: /* Since the full step didn't give sufficient decrease and the step is tiny, exit */
177: PetscCall(SNESLineSearchSetNorms(linesearch, xnorm, fnorm, ynorm));
178: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_SUCCEEDED));
179: if (monitor) {
180: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
181: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Ended due to ynorm < stol*xnorm (%14.12e < %14.12e).\n", (double)ynorm, (double)(stol * xnorm)));
182: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
183: }
184: PetscFunctionReturn(PETSC_SUCCESS);
185: }
186: /* Here to avoid -Wmaybe-uninitiliazed warnings */
187: lambdaprev = lambda;
188: gprev = g;
189: if (linesearch->order != SNES_LINESEARCH_ORDER_LINEAR) {
190: /* Fit points with quadratic */
191: lambdatemp = -initslope * PetscSqr(lambda) / (2.0 * (g - f - lambda * initslope));
192: lambda = PetscClipInterval(lambdatemp, .1 * lambda, .5 * lambda);
194: PetscCall(VecWAXPY(W, -lambda, Y, X));
195: if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W));
196: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
197: PetscCall(PetscInfo(snes, "Exceeded maximum function evaluations, while attempting quadratic backtracking! %" PetscInt_FMT " \n", snes->nfuncs));
198: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
199: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_FUNCTION));
200: PetscFunctionReturn(PETSC_SUCCESS);
201: }
202: if (objective) {
203: PetscCall(SNESComputeObjective(snes, W, &g));
204: SNESLineSearchCheckObjectiveDomainError(snes, g);
205: } else {
206: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
207: if (linesearch->ops->vinorm) {
208: gnorm = fnorm;
209: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
210: } else {
211: PetscCall(VecNorm(G, NORM_2, &gnorm));
212: }
213: SNESLineSearchCheckFunctionDomainError(snes, linesearch, gnorm);
214: g = 0.5 * PetscSqr(gnorm);
215: }
216: if (PetscIsInfOrNanReal(g)) {
217: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_NANORINF));
218: PetscCall(PetscInfo(snes, "Aborted due to infinity or NaN in function evaluation\n"));
219: PetscFunctionReturn(PETSC_SUCCESS);
220: }
221: if (monitor) {
222: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
223: if (!objective) {
224: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: gnorm after quadratic fit %14.12e\n", (double)gnorm));
225: } else {
226: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: obj after quadratic fit %14.12e\n", (double)g));
227: }
228: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
229: }
230: }
231: if (linesearch->order != SNES_LINESEARCH_ORDER_LINEAR && g <= f + lambda * alpha * initslope) { /* sufficient reduction */
232: if (monitor) {
233: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
234: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: Quadratically determined step, lambda=%18.16e\n", (double)lambda));
235: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
236: }
237: } else {
238: for (count = 0; count < max_it; count++) {
239: if (lambda <= minlambda) {
240: if (monitor) {
241: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
242: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: unable to find good step length! After %" PetscInt_FMT " tries \n", count));
243: if (!objective) {
244: 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));
245: } else {
246: 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));
247: }
248: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
249: }
250: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_REDUCT));
251: PetscFunctionReturn(PETSC_SUCCESS);
252: }
253: if (linesearch->order == SNES_LINESEARCH_ORDER_CUBIC) {
254: /* Fit points with cubic */
255: t1 = g - f - lambda * initslope;
256: t2 = gprev - f - lambdaprev * initslope;
257: a = (t1 / (lambda * lambda) - t2 / (lambdaprev * lambdaprev)) / (lambda - lambdaprev);
258: b = (-lambdaprev * t1 / (lambda * lambda) + lambda * t2 / (lambdaprev * lambdaprev)) / (lambda - lambdaprev);
259: d = b * b - 3 * a * initslope;
260: if (d < 0.0) d = 0.0;
261: if (a == 0.0) lambdatemp = -initslope / (2.0 * b);
262: else lambdatemp = (-b + PetscSqrtReal(d)) / (3.0 * a);
263: } else if (linesearch->order == SNES_LINESEARCH_ORDER_QUADRATIC) {
264: lambdatemp = -initslope * PetscSqr(lambda) / (2.0 * (g - f - lambda * initslope));
265: } else if (linesearch->order == SNES_LINESEARCH_ORDER_LINEAR) { /* Just backtrack */
266: lambdatemp = .5 * lambda;
267: } else SETERRQ(PetscObjectComm((PetscObject)linesearch), PETSC_ERR_SUP, "Line search order %" PetscInt_FMT " for type bt", linesearch->order);
268: lambdaprev = lambda;
269: gprev = g;
271: lambda = PetscClipInterval(lambdatemp, .1 * lambda, .5 * lambda);
272: PetscCall(VecWAXPY(W, -lambda, Y, X));
273: if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W));
274: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
275: PetscCall(PetscInfo(snes, "Exceeded maximum function evaluations, while looking for good step length! %" PetscInt_FMT " \n", count));
276: 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));
277: PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_FUNCTION));
278: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
279: PetscFunctionReturn(PETSC_SUCCESS);
280: }
281: if (objective) {
282: PetscCall(SNESComputeObjective(snes, W, &g));
283: SNESLineSearchCheckObjectiveDomainError(snes, g);
284: } else {
285: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
286: if (linesearch->ops->vinorm) {
287: gnorm = fnorm;
288: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
289: } else {
290: PetscCall(VecNorm(G, NORM_2, &gnorm));
291: }
292: SNESLineSearchCheckFunctionDomainError(snes, linesearch, gnorm);
293: g = 0.5 * PetscSqr(gnorm);
294: }
295: if (g <= f + lambda * alpha * initslope) { /* is reduction enough? */
296: if (monitor) {
297: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
298: if (!objective) {
299: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: %s step, current gnorm %14.12e lambda=%18.16e\n", ordStr[linesearch->order - 1], (double)gnorm, (double)lambda));
300: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
301: } else {
302: PetscCall(PetscViewerASCIIPrintf(monitor, " Line search: %s step, obj %14.12e lambda=%18.16e\n", ordStr[linesearch->order - 1], (double)g, (double)lambda));
303: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
304: }
305: }
306: break;
307: } else if (monitor) {
308: PetscCall(PetscViewerASCIIAddTab(monitor, ((PetscObject)linesearch)->tablevel));
309: if (!objective) {
310: 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));
311: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
312: } else {
313: 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));
314: PetscCall(PetscViewerASCIISubtractTab(monitor, ((PetscObject)linesearch)->tablevel));
315: }
316: }
317: }
318: }
319: }
321: /* postcheck */
322: PetscCall(SNESLineSearchSetLambda(linesearch, lambda));
323: PetscCall(SNESLineSearchPostCheck(linesearch, X, Y, W, &changed_y, &changed_w));
324: if (changed_y) {
325: if (!changed_w) PetscCall(VecWAXPY(W, -lambda, Y, X));
326: if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W));
327: }
328: if (changed_y || changed_w || objective) { /* recompute the function norm if the step has changed or the objective isn't the norm */
329: PetscCall((*linesearch->ops->snesfunc)(snes, W, G));
330: if (linesearch->ops->vinorm) {
331: gnorm = fnorm;
332: PetscCall((*linesearch->ops->vinorm)(snes, G, W, &gnorm));
333: } else {
334: PetscCall(VecNorm(G, NORM_2, &gnorm));
335: }
336: SNESLineSearchCheckFunctionDomainError(snes, linesearch, gnorm);
337: PetscCall(VecNorm(Y, NORM_2, &ynorm));
338: }
340: /* copy the solution over */
341: PetscCall(VecCopy(W, X));
342: PetscCall(VecCopy(G, F));
343: PetscCall(VecNorm(X, NORM_2, &xnorm));
344: PetscCall(SNESLineSearchSetNorms(linesearch, xnorm, gnorm, ynorm));
345: PetscFunctionReturn(PETSC_SUCCESS);
346: }
348: static PetscErrorCode SNESLineSearchView_BT(SNESLineSearch linesearch, PetscViewer viewer)
349: {
350: PetscBool isascii;
351: SNESLineSearch_BT *bt = (SNESLineSearch_BT *)linesearch->data;
353: PetscFunctionBegin;
354: PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
355: if (isascii) {
356: if (linesearch->order == SNES_LINESEARCH_ORDER_CUBIC) {
357: PetscCall(PetscViewerASCIIPrintf(viewer, " interpolation: cubic\n"));
358: } else if (linesearch->order == SNES_LINESEARCH_ORDER_QUADRATIC) {
359: PetscCall(PetscViewerASCIIPrintf(viewer, " interpolation: quadratic\n"));
360: }
361: PetscCall(PetscViewerASCIIPrintf(viewer, " alpha=%e\n", (double)bt->alpha));
362: }
363: PetscFunctionReturn(PETSC_SUCCESS);
364: }
366: static PetscErrorCode SNESLineSearchDestroy_BT(SNESLineSearch linesearch)
367: {
368: PetscFunctionBegin;
369: PetscCall(PetscFree(linesearch->data));
370: PetscFunctionReturn(PETSC_SUCCESS);
371: }
373: static PetscErrorCode SNESLineSearchSetFromOptions_BT(SNESLineSearch linesearch, PetscOptionItems PetscOptionsObject)
374: {
375: SNESLineSearch_BT *bt = (SNESLineSearch_BT *)linesearch->data;
377: PetscFunctionBegin;
378: PetscOptionsHeadBegin(PetscOptionsObject, "SNESLineSearch BT options");
379: PetscCall(PetscOptionsReal("-snes_linesearch_alpha", "Descent tolerance", "SNESLineSearchBT", bt->alpha, &bt->alpha, NULL));
380: PetscOptionsHeadEnd();
381: PetscFunctionReturn(PETSC_SUCCESS);
382: }
384: /*MC
385: SNESLINESEARCHBT - Backtracking line search {cite}`dennis:83`.
387: This line search finds the minimum of a polynomial fitting either $1/2 ||F(x_k + \lambda Y_k)||_2^2$,
388: or the objective function $G(x_k + \lambda Y_k)$ if it is provided with `SNESSetObjective()`.
389: If this fit does not satisfy the sufficient decrease conditions, the interval shrinks
390: and the fit is reattempted at most `max_it` times or until $\lambda$ is below `minlambda`.
392: Options Database Keys:
393: + -snes_linesearch_alpha 1e\-4 - slope descent parameter
394: . -snes_linesearch_damping 1.0 - initial `lambda` on entry to the line search
395: . -snes_linesearch_max_it 40 - maximum number of shrinking iterations in the line search
396: . -snes_linesearch_minlambda 1e\-12 - minimum `lambda` (scaling of solution update) allowed
397: - -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
399: Level: advanced
401: Note:
402: This line search will always produce a step that is less than or equal to, in length, the full step size.
404: .seealso: [](ch_snes), `SNESLineSearch`, `SNESLineSearchType`, `SNESLineSearchCreate()`, `SNESLineSearchSetType()`
405: M*/
406: PETSC_EXTERN PetscErrorCode SNESLineSearchCreate_BT(SNESLineSearch linesearch)
407: {
408: SNESLineSearch_BT *bt;
410: PetscFunctionBegin;
411: linesearch->ops->apply = SNESLineSearchApply_BT;
412: linesearch->ops->destroy = SNESLineSearchDestroy_BT;
413: linesearch->ops->setfromoptions = SNESLineSearchSetFromOptions_BT;
414: linesearch->ops->reset = NULL;
415: linesearch->ops->view = SNESLineSearchView_BT;
416: linesearch->ops->setup = NULL;
418: PetscCall(PetscNew(&bt));
420: linesearch->data = (void *)bt;
421: linesearch->max_it = 40;
422: linesearch->order = SNES_LINESEARCH_ORDER_CUBIC;
423: bt->alpha = 1e-4;
424: PetscFunctionReturn(PETSC_SUCCESS);
425: }