Date: 2026-01-20T11:35:39+00:00

Actual source code: test27.c

      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[] = "Illustrates feeding exact eigenvectors as initial vectors of a second solve.\n\n"
     12:   "Based on ex2.\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\n";

     17: #include <slepceps.h>

     19: int main(int argc,char **argv)
     20: {
     21:   Mat            A;
     22:   EPS            eps;
     23:   PetscInt       N,n=10,m,Istart,Iend,II,nev,nconv,i,j,neigs=5;
     24:   PetscBool      flag,terse;
     25:   Vec            v,*X;

     27:   PetscFunctionBeginUser;
     28:   PetscCall(SlepcInitialize(&argc,&argv,NULL,help));
     29:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL));
     30:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag));
     31:   if (!flag) m=n;
     32:   N = n*m;
     33:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-neigs",&neigs,NULL));
     34:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\n2-D Laplacian Eigenproblem, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid), neigs=%" PetscInt_FMT "\n\n",N,n,m,neigs));

     36:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     37:                     Create the 2-D Laplacian
     38:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     40:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
     41:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N));
     42:   PetscCall(MatSetFromOptions(A));
     43:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
     44:   for (II=Istart;II<Iend;II++) {
     45:     i = II/n; j = II-i*n;
     46:     if (i>0) PetscCall(MatSetValue(A,II,II-n,-1.0,INSERT_VALUES));
     47:     if (i<m-1) PetscCall(MatSetValue(A,II,II+n,-1.0,INSERT_VALUES));
     48:     if (j>0) PetscCall(MatSetValue(A,II,II-1,-1.0,INSERT_VALUES));
     49:     if (j<n-1) PetscCall(MatSetValue(A,II,II+1,-1.0,INSERT_VALUES));
     50:     PetscCall(MatSetValue(A,II,II,4.0,INSERT_VALUES));
     51:   }
     52:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
     53:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));
     54:   PetscCall(MatCreateVecs(A,&v,NULL));

     56:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     57:                 Create the eigensolver and set various options
     58:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     60:   PetscCall(EPSCreate(PETSC_COMM_WORLD,&eps));
     61:   PetscCall(EPSSetOperators(eps,A,NULL));
     62:   PetscCall(EPSSetProblemType(eps,EPS_HEP));
     63:   PetscCall(EPSSetWhichEigenpairs(eps,EPS_SMALLEST_REAL));
     64:   PetscCall(EPSSetDimensions(eps,neigs,PETSC_DETERMINE,PETSC_DETERMINE));
     65:   PetscCall(EPSSetFromOptions(eps));

     67:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     68:                 Solve the eigensystem for the first time
     69:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     71:   PetscCall(EPSSolve(eps));
     72:   PetscCall(EPSGetDimensions(eps,&nev,NULL,NULL));
     73:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," Number of requested eigenvalues: %" PetscInt_FMT "\n",nev));

     75:   PetscCall(EPSGetConverged(eps,&nconv));
     76:   PetscCheck(nconv>=neigs,PETSC_COMM_WORLD,PETSC_ERR_CONV_FAILED,"Only %" PetscInt_FMT " eigenvalues have converged, %" PetscInt_FMT " requested",nconv,neigs);
     77:   PetscCall(VecDuplicateVecs(v,neigs,&X));
     78:   for (i=0;i<neigs;i++) PetscCall(EPSGetEigenvector(eps,i,X[i],NULL));

     80:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     81:                     Display solution of first solve
     82:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     84:   PetscCall(PetscOptionsHasName(NULL,NULL,"-terse",&terse));
     85:   if (terse) PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL));
     86:   else {
     87:     PetscCall(PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO_DETAIL));
     88:     PetscCall(EPSConvergedReasonView(eps,PETSC_VIEWER_STDOUT_WORLD));
     89:     PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,PETSC_VIEWER_STDOUT_WORLD));
     90:     PetscCall(PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD));
     91:   }

     93:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     94:           Solve the eigensystem again, feeding the initial vectors
     95:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     97:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," Solving again with eigenvectors as initial guesses\n"));
     98:   PetscCall(EPSSetInitialSpace(eps,neigs,X));
     99:   PetscCall(EPSSolve(eps));

    101:   if (terse) PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL));
    102:   else {
    103:     PetscCall(PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO_DETAIL));
    104:     PetscCall(EPSConvergedReasonView(eps,PETSC_VIEWER_STDOUT_WORLD));
    105:     PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,PETSC_VIEWER_STDOUT_WORLD));
    106:     PetscCall(PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD));
    107:   }

    109:   PetscCall(VecDestroy(&v));
    110:   PetscCall(VecDestroyVecs(neigs,&X));
    111:   PetscCall(EPSDestroy(&eps));
    112:   PetscCall(MatDestroy(&A));
    113:   PetscCall(SlepcFinalize());
    114:   return 0;
    115: }

    117: /*TEST

    119:    test:
    120:       suffix: 1
    121:       args: -eps_type {{gd jd rqcg lobpcg}} -terse

    123:    testset:
    124:       args: -eps_interval .17,1.3 -terse
    125:       filter: grep -v "requested"
    126:       output_file: output/test27_2.out
    127:       test:
    128:          suffix: 2
    129:          args: -st_type filter -st_filter_degree 150 -st_filter_type {{filtlan chebyshev}} -eps_ncv 30
    130:          requires: !single
    131:       test:
    132:          suffix: 2_evsl
    133:          nsize: {{1 2}}
    134:          args: -eps_type evsl
    135:          requires: evsl

    137: TEST*/