1 #include <petsc/private/linesearchimpl.h> 2 #include <petsc/private/snesimpl.h> 3 4 static PetscErrorCode SNESLineSearchApply_Basic(SNESLineSearch linesearch) 5 { 6 PetscBool changed_y, changed_w; 7 Vec X, F, Y, W; 8 SNES snes; 9 PetscReal gnorm, xnorm, ynorm, lambda, fnorm = 0.0; 10 11 PetscFunctionBegin; 12 PetscCall(SNESLineSearchGetVecs(linesearch, &X, &F, &Y, &W, NULL)); 13 PetscCall(SNESLineSearchGetNorms(linesearch, &xnorm, &gnorm, &ynorm)); 14 PetscCall(SNESLineSearchGetLambda(linesearch, &lambda)); 15 PetscCall(SNESLineSearchGetSNES(linesearch, &snes)); 16 PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_SUCCEEDED)); 17 18 /* precheck */ 19 PetscCall(SNESLineSearchPreCheck(linesearch, X, Y, &changed_y)); 20 21 /* update */ 22 PetscCall(VecWAXPY(W, -lambda, Y, X)); 23 if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W)); 24 25 /* postcheck */ 26 PetscCall(SNESLineSearchPostCheck(linesearch, X, Y, W, &changed_y, &changed_w)); 27 if (changed_y) { 28 if (!changed_w) PetscCall(VecWAXPY(W, -lambda, Y, X)); 29 if (linesearch->ops->viproject) PetscCall((*linesearch->ops->viproject)(snes, W)); 30 } 31 if (linesearch->norms || snes->iter < snes->max_its - 1) { 32 PetscCall((*linesearch->ops->snesfunc)(snes, W, F)); 33 PetscCall(VecNorm(F, NORM_2, &fnorm)); 34 } 35 if (linesearch->norms) { 36 PetscCall(VecNormBegin(Y, NORM_2, &linesearch->ynorm)); 37 PetscCall(VecNormBegin(W, NORM_2, &linesearch->xnorm)); 38 PetscCall(VecNormEnd(Y, NORM_2, &linesearch->ynorm)); 39 PetscCall(VecNormEnd(W, NORM_2, &linesearch->xnorm)); 40 41 if (linesearch->ops->vinorm) { 42 linesearch->fnorm = gnorm; 43 44 PetscCall((*linesearch->ops->vinorm)(snes, F, W, &linesearch->fnorm)); 45 } else linesearch->fnorm = fnorm; 46 } 47 if (PetscIsInfOrNanReal(fnorm)) { 48 PetscCall(SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_DOMAIN)); 49 PetscFunctionReturn(PETSC_SUCCESS); 50 } 51 52 /* copy the solution over */ 53 PetscCall(VecCopy(W, X)); 54 PetscFunctionReturn(PETSC_SUCCESS); 55 } 56 57 /*MC 58 SNESLINESEARCHBASIC - This line search implementation is not a line 59 search at all; it simply uses the full step $x_{k+1} = x_k - \lambda Y_k$ with $\lambda=1$. 60 Alternatively, $\lambda$ can be configured to be a constant damping factor by setting `snes_linesearch_damping`. 61 Thus, this routine is intended for methods with well-scaled updates; i.e. Newton's method (`SNESNEWTONLS`), on 62 well-behaved problems. Also named `SNESLINESEARCHNONE`. 63 64 Options Database Keys: 65 + -snes_linesearch_damping <1.0> - step length is scaled by this factor 66 - -snes_linesearch_norms <true> - whether to compute norms or not (`SNESLineSearchSetComputeNorms()`) 67 68 Note: 69 For methods with ill-scaled updates (`SNESNRICHARDSON`, `SNESNCG`), a small 70 damping parameter may yield satisfactory, but slow convergence, despite 71 the lack of the line search. 72 73 Level: advanced 74 75 .seealso: [](ch_snes), `SNES`, `SNESLineSearch`, `SNESLineSearchType`, `SNESGetLineSearch()`, `SNESLineSearchCreate()`, `SNESLineSearchSetType()`, `SNESLineSearchSetDamping()`, `SNESLineSearchSetComputeNorms()` 76 M*/ 77 PETSC_EXTERN PetscErrorCode SNESLineSearchCreate_Basic(SNESLineSearch linesearch) 78 { 79 PetscFunctionBegin; 80 linesearch->ops->apply = SNESLineSearchApply_Basic; 81 linesearch->ops->destroy = NULL; 82 linesearch->ops->setfromoptions = NULL; 83 linesearch->ops->reset = NULL; 84 linesearch->ops->view = NULL; 85 linesearch->ops->setup = NULL; 86 PetscFunctionReturn(PETSC_SUCCESS); 87 } 88