Actual source code: ex35.c
slepc-3.17.2 2022-08-09
1: /*
2: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
3: SLEPc - Scalable Library for Eigenvalue Problem Computations
4: Copyright (c) 2002-, Universitat Politecnica de Valencia, Spain
6: This file is part of SLEPc.
7: SLEPc is distributed under a 2-clause BSD license (see LICENSE).
8: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
9: */
11: static char help[] = "Shell spectral transformations with a non-injective mapping. "
12: "Implements spectrum folding for the 2-D Laplacian, as in ex24.c.\n\n"
13: "The command line options are:\n"
14: " -n <n>, where <n> = number of grid subdivisions in x dimension.\n"
15: " -m <m>, where <m> = number of grid subdivisions in y dimension.\n";
17: #include <slepceps.h>
19: /* Context for spectrum folding spectral transformation */
20: typedef struct {
21: Mat A;
22: Vec w;
23: PetscScalar target;
24: } FoldShellST;
26: /* Routines for shell spectral transformation */
27: PetscErrorCode STCreate_Fold(Mat,PetscScalar,FoldShellST**);
28: PetscErrorCode STApply_Fold(ST,Vec,Vec);
29: PetscErrorCode STDestroy_Fold(FoldShellST*);
31: int main (int argc,char **argv)
32: {
33: Mat A; /* operator matrix */
34: EPS eps; /* eigenproblem solver context */
35: ST st; /* spectral transformation context */
36: FoldShellST *fold; /* user-defined spectral transform context */
37: EPSType type;
38: PetscInt N,n=10,m,i,j,II,Istart,Iend,nev;
39: PetscBool isShell,terse,flag;
40: PetscScalar target=1.1;
42: SlepcInitialize(&argc,&argv,(char*)0,help);
44: PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
45: PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag);
46: if (!flag) m = n;
47: PetscOptionsGetScalar(NULL,NULL,"-target",&target,NULL);
48: N = n*m;
49: PetscPrintf(PETSC_COMM_WORLD,"\nSpectrum Folding via shell ST, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid) target=%3.2f\n\n",N,n,m,(double)PetscRealPart(target));
51: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
52: Compute the 5-point stencil Laplacian
53: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
55: MatCreate(PETSC_COMM_WORLD,&A);
56: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);
57: MatSetFromOptions(A);
58: MatSetUp(A);
60: MatGetOwnershipRange(A,&Istart,&Iend);
61: for (II=Istart;II<Iend;II++) {
62: i = II/n; j = II-i*n;
63: if (i>0) MatSetValue(A,II,II-n,-1.0,INSERT_VALUES);
64: if (i<m-1) MatSetValue(A,II,II+n,-1.0,INSERT_VALUES);
65: if (j>0) MatSetValue(A,II,II-1,-1.0,INSERT_VALUES);
66: if (j<n-1) MatSetValue(A,II,II+1,-1.0,INSERT_VALUES);
67: MatSetValue(A,II,II,4.0,INSERT_VALUES);
68: }
69: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
70: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
72: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73: Create the eigensolver and set various options
74: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
76: EPSCreate(PETSC_COMM_WORLD,&eps);
77: EPSSetOperators(eps,A,NULL);
78: EPSSetProblemType(eps,EPS_HEP);
79: EPSSetTarget(eps,target);
80: EPSGetST(eps,&st);
81: STSetType(st,STSHELL);
82: EPSSetFromOptions(eps);
84: /*
85: Initialize shell spectral transformation
86: */
87: PetscObjectTypeCompare((PetscObject)st,STSHELL,&isShell);
88: if (isShell) {
89: /* Change sorting criterion since this shell ST computes eigenvalues
90: of the transformed operator closest to 0 */
91: EPSSetWhichEigenpairs(eps,EPS_SMALLEST_REAL);
93: /* Create the context for the user-defined spectral transform */
94: STCreate_Fold(A,target,&fold);
95: STShellSetContext(st,fold);
97: /* Set callback function for applying the operator (in this case we do not
98: provide a back-transformation callback since the mapping is not one-to-one) */
99: STShellSetApply(st,STApply_Fold);
100: PetscObjectSetName((PetscObject)st,"STFOLD");
101: }
103: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
104: Solve the eigensystem
105: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
107: EPSSolve(eps);
108: EPSGetType(eps,&type);
109: PetscPrintf(PETSC_COMM_WORLD," Solution method: %s\n\n",type);
110: EPSGetDimensions(eps,&nev,NULL,NULL);
111: PetscPrintf(PETSC_COMM_WORLD," Number of requested eigenvalues: %" PetscInt_FMT "\n",nev);
113: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
114: Display solution and clean up
115: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
117: /* show detailed info unless -terse option is given by user */
118: PetscOptionsHasName(NULL,NULL,"-terse",&terse);
119: if (terse) EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL);
120: else {
121: PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO_DETAIL);
122: EPSConvergedReasonView(eps,PETSC_VIEWER_STDOUT_WORLD);
123: EPSErrorView(eps,EPS_ERROR_RELATIVE,PETSC_VIEWER_STDOUT_WORLD);
124: PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD);
125: }
126: if (isShell) STDestroy_Fold(fold);
127: EPSDestroy(&eps);
128: MatDestroy(&A);
129: SlepcFinalize();
130: return 0;
131: }
133: /*
134: STCreate_Fold - Creates the spectrum folding ST context.
136: Input Parameter:
137: + A - problem matrix
138: - target - target value
140: Output Parameter:
141: . fold - user-defined spectral transformation context
142: */
143: PetscErrorCode STCreate_Fold(Mat A,PetscScalar target,FoldShellST **fold)
144: {
145: FoldShellST *newctx;
148: PetscNew(&newctx);
149: newctx->A = A;
150: PetscObjectReference((PetscObject)A);
151: newctx->target = target;
152: MatCreateVecs(A,&newctx->w,NULL);
153: *fold = newctx;
154: PetscFunctionReturn(0);
155: }
157: /*
158: STApply_Fold - Applies the operator (A-target*I)^2 to a given vector.
160: Input Parameters:
161: + st - spectral transformation context
162: - x - input vector
164: Output Parameter:
165: . y - output vector
166: */
167: PetscErrorCode STApply_Fold(ST st,Vec x,Vec y)
168: {
169: FoldShellST *fold;
170: PetscScalar sigma;
173: STShellGetContext(st,&fold);
174: sigma = -fold->target;
175: MatMult(fold->A,x,fold->w);
176: VecAXPY(fold->w,sigma,x);
177: MatMult(fold->A,fold->w,y);
178: VecAXPY(y,sigma,fold->w);
179: PetscFunctionReturn(0);
180: }
182: /*
183: STDestroy_Fold - This routine destroys the shell ST context.
185: Input Parameter:
186: . fold - user-defined spectral transformation context
187: */
188: PetscErrorCode STDestroy_Fold(FoldShellST *fold)
189: {
191: MatDestroy(&fold->A);
192: VecDestroy(&fold->w);
193: PetscFree(fold);
194: PetscFunctionReturn(0);
195: }
197: /*TEST
199: test:
200: args: -m 11 -eps_nev 4 -terse
201: suffix: 1
202: requires: !single
204: TEST*/