Actual source code: ex35.c

slepc-3.17.2 2022-08-09
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  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*/