Actual source code: ex35.c

slepc-main 2024-11-15
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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:   PetscFunctionBeginUser;
 43:   PetscCall(SlepcInitialize(&argc,&argv,NULL,help));

 45:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL));
 46:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag));
 47:   if (!flag) m = n;
 48:   PetscCall(PetscOptionsGetScalar(NULL,NULL,"-target",&target,NULL));
 49:   N = n*m;
 50:   PetscCall(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)));

 52:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 53:      Compute the 5-point stencil Laplacian
 54:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 56:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
 57:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N));
 58:   PetscCall(MatSetFromOptions(A));

 60:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
 61:   for (II=Istart;II<Iend;II++) {
 62:     i = II/n; j = II-i*n;
 63:     if (i>0) PetscCall(MatSetValue(A,II,II-n,-1.0,INSERT_VALUES));
 64:     if (i<m-1) PetscCall(MatSetValue(A,II,II+n,-1.0,INSERT_VALUES));
 65:     if (j>0) PetscCall(MatSetValue(A,II,II-1,-1.0,INSERT_VALUES));
 66:     if (j<n-1) PetscCall(MatSetValue(A,II,II+1,-1.0,INSERT_VALUES));
 67:     PetscCall(MatSetValue(A,II,II,4.0,INSERT_VALUES));
 68:   }
 69:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
 70:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

 72:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 73:                 Create the eigensolver and set various options
 74:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 76:   PetscCall(EPSCreate(PETSC_COMM_WORLD,&eps));
 77:   PetscCall(EPSSetOperators(eps,A,NULL));
 78:   PetscCall(EPSSetProblemType(eps,EPS_HEP));
 79:   PetscCall(EPSSetTarget(eps,target));
 80:   PetscCall(EPSGetST(eps,&st));
 81:   PetscCall(STSetType(st,STSHELL));
 82:   PetscCall(EPSSetFromOptions(eps));

 84:   /*
 85:      Initialize shell spectral transformation
 86:   */
 87:   PetscCall(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:     PetscCall(EPSSetWhichEigenpairs(eps,EPS_SMALLEST_REAL));

 93:     /* Create the context for the user-defined spectral transform */
 94:     PetscCall(STCreate_Fold(A,target,&fold));
 95:     PetscCall(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:     PetscCall(STShellSetApply(st,STApply_Fold));
100:     PetscCall(PetscObjectSetName((PetscObject)st,"STFOLD"));
101:   }

103:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
104:                       Solve the eigensystem
105:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

107:   PetscCall(EPSSolve(eps));
108:   PetscCall(EPSGetType(eps,&type));
109:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," Solution method: %s\n\n",type));
110:   PetscCall(EPSGetDimensions(eps,&nev,NULL,NULL));
111:   PetscCall(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:   PetscCall(PetscOptionsHasName(NULL,NULL,"-terse",&terse));
119:   if (terse) PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL));
120:   else {
121:     PetscCall(PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO_DETAIL));
122:     PetscCall(EPSConvergedReasonView(eps,PETSC_VIEWER_STDOUT_WORLD));
123:     PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,PETSC_VIEWER_STDOUT_WORLD));
124:     PetscCall(PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD));
125:   }
126:   if (isShell) PetscCall(STDestroy_Fold(fold));
127:   PetscCall(EPSDestroy(&eps));
128:   PetscCall(MatDestroy(&A));
129:   PetscCall(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;

147:   PetscFunctionBeginUser;
148:   PetscCall(PetscNew(&newctx));
149:   newctx->A = A;
150:   PetscCall(PetscObjectReference((PetscObject)A));
151:   newctx->target = target;
152:   PetscCall(MatCreateVecs(A,&newctx->w,NULL));
153:   *fold = newctx;
154:   PetscFunctionReturn(PETSC_SUCCESS);
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;

172:   PetscFunctionBeginUser;
173:   PetscCall(STShellGetContext(st,&fold));
174:   sigma = -fold->target;
175:   PetscCall(MatMult(fold->A,x,fold->w));
176:   PetscCall(VecAXPY(fold->w,sigma,x));
177:   PetscCall(MatMult(fold->A,fold->w,y));
178:   PetscCall(VecAXPY(y,sigma,fold->w));
179:   PetscFunctionReturn(PETSC_SUCCESS);
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: {
190:   PetscFunctionBeginUser;
191:   PetscCall(MatDestroy(&fold->A));
192:   PetscCall(VecDestroy(&fold->w));
193:   PetscCall(PetscFree(fold));
194:   PetscFunctionReturn(PETSC_SUCCESS);
195: }

197: /*TEST

199:    test:
200:       args: -m 11 -eps_nev 4 -terse
201:       suffix: 1
202:       requires: !single

204: TEST*/