1 /*MC 2 MATMFFD_WP - Implements an approach for computing the differencing parameter 3 h used with the finite difference based matrix-free Jacobian. From Walker-Pernice {cite}`pw98` 4 5 $$ 6 h = error_rel * sqrt(1 + ||u||) / ||a|| 7 $$ 8 9 Options Database Key: 10 . -mat_mffd_compute_normu -Compute the norm of u every time see `MatMFFDWPSetComputeNormU()` 11 12 Level: intermediate 13 14 Notes: 15 $ || U || $ does not change between linear iterations so is reused 16 17 In `KSPGMRES` $ || a || == 1 $ and so does not need to ever be computed except at restart 18 when it is recomputed. Thus requires no global collectives when used with `KSPGMRES` 19 20 .seealso: `MATMFFD`, `MATMFFD_DS`, `MatCreateMFFD()`, `MatCreateSNESMF()`, `MATMFFD_DS` 21 M*/ 22 23 /* 24 This include file defines the data structure MatMFFD that 25 includes information about the computation of h. It is shared by 26 all implementations that people provide. 27 28 See snesmfjdef.c for a full set of comments on the routines below. 29 */ 30 #include <petsc/private/matimpl.h> 31 #include <../src/mat/impls/mffd/mffdimpl.h> /*I "petscmat.h" I*/ 32 33 typedef struct { 34 PetscReal normUfact; /* previous sqrt(1.0 + || U ||) */ 35 PetscBool computenormU; 36 } MatMFFD_WP; 37 38 /* 39 MatMFFDCompute_WP - code for 40 computing h with matrix-free finite differences. 41 42 Input Parameters: 43 + ctx - the matrix-free context 44 . U - the location at which you want the Jacobian 45 - a - the direction you want the derivative 46 47 Output Parameter: 48 . h - the scale computed 49 */ 50 static PetscErrorCode MatMFFDCompute_WP(MatMFFD ctx, Vec U, Vec a, PetscScalar *h, PetscBool *zeroa) 51 { 52 MatMFFD_WP *hctx = (MatMFFD_WP *)ctx->hctx; 53 PetscReal normU, norma; 54 55 PetscFunctionBegin; 56 if (!(ctx->count % ctx->recomputeperiod)) { 57 if (hctx->computenormU || !ctx->ncurrenth) { 58 PetscCall(VecNorm(U, NORM_2, &normU)); 59 hctx->normUfact = PetscSqrtReal(1.0 + normU); 60 } 61 PetscCall(VecNorm(a, NORM_2, &norma)); 62 if (norma == 0.0) { 63 *zeroa = PETSC_TRUE; 64 PetscFunctionReturn(PETSC_SUCCESS); 65 } 66 *zeroa = PETSC_FALSE; 67 *h = ctx->error_rel * hctx->normUfact / norma; 68 } else { 69 *h = ctx->currenth; 70 } 71 PetscFunctionReturn(PETSC_SUCCESS); 72 } 73 74 /* 75 MatMFFDView_WP - Prints information about this particular 76 method for computing h. Note that this does not print the general 77 information about the matrix-free, that is printed by the calling 78 routine. 79 80 Input Parameters: 81 + ctx - the matrix-free context 82 - viewer - the PETSc viewer 83 84 */ 85 static PetscErrorCode MatMFFDView_WP(MatMFFD ctx, PetscViewer viewer) 86 { 87 MatMFFD_WP *hctx = (MatMFFD_WP *)ctx->hctx; 88 PetscBool iascii; 89 90 PetscFunctionBegin; 91 PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &iascii)); 92 if (iascii) { 93 if (hctx->computenormU) { 94 PetscCall(PetscViewerASCIIPrintf(viewer, " Computes normU\n")); 95 } else { 96 PetscCall(PetscViewerASCIIPrintf(viewer, " Does not compute normU\n")); 97 } 98 } 99 PetscFunctionReturn(PETSC_SUCCESS); 100 } 101 102 /* 103 MatMFFDSetFromOptions_WP - Looks in the options database for 104 any options appropriate for this method 105 106 Input Parameter: 107 . ctx - the matrix-free context 108 109 */ 110 static PetscErrorCode MatMFFDSetFromOptions_WP(MatMFFD ctx, PetscOptionItems PetscOptionsObject) 111 { 112 MatMFFD_WP *hctx = (MatMFFD_WP *)ctx->hctx; 113 114 PetscFunctionBegin; 115 PetscOptionsHeadBegin(PetscOptionsObject, "Walker-Pernice options"); 116 PetscCall(PetscOptionsBool("-mat_mffd_compute_normu", "Compute the norm of u", "MatMFFDWPSetComputeNormU", hctx->computenormU, &hctx->computenormU, NULL)); 117 PetscOptionsHeadEnd(); 118 PetscFunctionReturn(PETSC_SUCCESS); 119 } 120 121 static PetscErrorCode MatMFFDDestroy_WP(MatMFFD ctx) 122 { 123 PetscFunctionBegin; 124 PetscCall(PetscObjectComposeFunction((PetscObject)ctx->mat, "MatMFFDWPSetComputeNormU_C", NULL)); 125 PetscCall(PetscFree(ctx->hctx)); 126 PetscFunctionReturn(PETSC_SUCCESS); 127 } 128 129 static PetscErrorCode MatMFFDWPSetComputeNormU_P(Mat mat, PetscBool flag) 130 { 131 MatMFFD ctx = (MatMFFD)mat->data; 132 MatMFFD_WP *hctx = (MatMFFD_WP *)ctx->hctx; 133 134 PetscFunctionBegin; 135 hctx->computenormU = flag; 136 PetscFunctionReturn(PETSC_SUCCESS); 137 } 138 139 /*@ 140 MatMFFDWPSetComputeNormU - Sets whether it computes the ||U|| used by the Walker-Pernice {cite}`pw98` 141 PETSc routine for computing h. With any Krylov solver this need only 142 be computed during the first iteration and kept for later. 143 144 Input Parameters: 145 + A - the `MATMFFD` matrix 146 - flag - `PETSC_TRUE` causes it to compute $||U||$, `PETSC_FALSE` uses the previous value 147 148 Options Database Key: 149 . -mat_mffd_compute_normu <true,false> - true by default, false can save calculations but you 150 must be sure that $||U||$ has not changed in the mean time. 151 152 Level: advanced 153 154 Note: 155 See the manual page for `MATMFFD_WP` for a complete description of the 156 algorithm used to compute h. 157 158 .seealso: `MATMFFD_WP`, `MATMFFD`, `MatMFFDSetFunctionError()`, `MatCreateSNESMF()` 159 @*/ 160 PetscErrorCode MatMFFDWPSetComputeNormU(Mat A, PetscBool flag) 161 { 162 PetscFunctionBegin; 163 PetscValidHeaderSpecific(A, MAT_CLASSID, 1); 164 PetscTryMethod(A, "MatMFFDWPSetComputeNormU_C", (Mat, PetscBool), (A, flag)); 165 PetscFunctionReturn(PETSC_SUCCESS); 166 } 167 168 /* 169 MatCreateMFFD_WP - Standard PETSc code for 170 computing h with matrix-free finite differences. 171 172 Input Parameter: 173 . ctx - the matrix-free context created by MatCreateMFFD() 174 175 */ 176 PETSC_EXTERN PetscErrorCode MatCreateMFFD_WP(MatMFFD ctx) 177 { 178 MatMFFD_WP *hctx; 179 180 PetscFunctionBegin; 181 /* allocate my own private data structure */ 182 PetscCall(PetscNew(&hctx)); 183 ctx->hctx = (void *)hctx; 184 hctx->computenormU = PETSC_FALSE; 185 186 /* set the functions I am providing */ 187 ctx->ops->compute = MatMFFDCompute_WP; 188 ctx->ops->destroy = MatMFFDDestroy_WP; 189 ctx->ops->view = MatMFFDView_WP; 190 ctx->ops->setfromoptions = MatMFFDSetFromOptions_WP; 191 192 PetscCall(PetscObjectComposeFunction((PetscObject)ctx->mat, "MatMFFDWPSetComputeNormU_C", MatMFFDWPSetComputeNormU_P)); 193 PetscFunctionReturn(PETSC_SUCCESS); 194 } 195