Date: 2024-04-26T10:22:07+00:00

Actual source code: ex46.c
slepc-3.21.1 2024-04-26
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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[] = "Illustrates passing a sparser matrix to build the preconditioner.\n\n"
     12:   "The command line options are:\n"
     13:   "  -n <n>, where <n> = number of grid subdivisions in x dimension.\n"
     14:   "  -m <m>, where <m> = number of grid subdivisions in y dimension.\n\n";

     16: #include <slepceps.h>

     18: int main(int argc,char **argv)
     19: {
     20:   Mat            A,A0;            /* operator matrix */
     21:   EPS            eps;             /* eigenproblem solver context */
     22:   ST             st;
     23:   PetscInt       N,n=24,m,Istart,Iend,II,i,j;
     24:   PetscBool      flag,terse;

     26:   PetscFunctionBeginUser;
     27:   PetscCall(SlepcInitialize(&argc,&argv,(char*)0,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(PetscPrintf(PETSC_COMM_WORLD,"\nModified 2-D Laplacian Eigenproblem, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid)\n\n",N,n,m));

     35:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     36:        Compute the operator matrix A and a sparser approximation A0
     37:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     39:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
     40:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N));
     41:   PetscCall(MatSetFromOptions(A));
     42:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
     43:   for (II=Istart;II<Iend;II++) {
     44:     i = II/n; j = II-i*n;
     45:     if (i>0) PetscCall(MatSetValue(A,II,II-n,-0.2,INSERT_VALUES));
     46:     if (i<m-1) PetscCall(MatSetValue(A,II,II+n,-0.2,INSERT_VALUES));
     47:     if (j>0) PetscCall(MatSetValue(A,II,II-1,-3.0,INSERT_VALUES));
     48:     if (j<n-1) PetscCall(MatSetValue(A,II,II+1,-3.0,INSERT_VALUES));
     49:     PetscCall(MatSetValue(A,II,II,7.0,INSERT_VALUES));
     50:   }
     51:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
     52:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

     54:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A0));
     55:   PetscCall(MatSetSizes(A0,PETSC_DECIDE,PETSC_DECIDE,N,N));
     56:   PetscCall(MatSetFromOptions(A0));
     57:   PetscCall(MatGetOwnershipRange(A0,&Istart,&Iend));
     58:   for (II=Istart;II<Iend;II++) {
     59:     i = II/n; j = II-i*n;
     60:     if (j>0) PetscCall(MatSetValue(A0,II,II-1,-3.0,INSERT_VALUES));
     61:     if (j<n-1) PetscCall(MatSetValue(A0,II,II+1,-3.0,INSERT_VALUES));
     62:     PetscCall(MatSetValue(A0,II,II,7.0,INSERT_VALUES));
     63:   }
     64:   PetscCall(MatAssemblyBegin(A0,MAT_FINAL_ASSEMBLY));
     65:   PetscCall(MatAssemblyEnd(A0,MAT_FINAL_ASSEMBLY));

     67:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     68:                 Create the eigensolver and set various options
     69:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     71:   PetscCall(EPSCreate(PETSC_COMM_WORLD,&eps));
     72:   PetscCall(EPSSetOperators(eps,A,NULL));
     73:   PetscCall(EPSSetProblemType(eps,EPS_HEP));
     74:   PetscCall(EPSGetST(eps,&st));
     75:   PetscCall(STSetType(st,STSINVERT));
     76:   PetscCall(STSetPreconditionerMat(st,A0));
     77:   PetscCall(EPSSetTarget(eps,0.0));
     78:   PetscCall(EPSSetWhichEigenpairs(eps,EPS_TARGET_MAGNITUDE));
     79:   PetscCall(EPSSetFromOptions(eps));

     81:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     82:                  Solve the eigensystem and display solution
     83:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     85:   PetscCall(EPSSolve(eps));

     87:   /* show detailed info unless -terse option is given by user */
     88:   PetscCall(PetscOptionsHasName(NULL,NULL,"-terse",&terse));
     89:   if (terse) PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL));
     90:   else {
     91:     PetscCall(PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO_DETAIL));
     92:     PetscCall(EPSConvergedReasonView(eps,PETSC_VIEWER_STDOUT_WORLD));
     93:     PetscCall(EPSErrorView(eps,EPS_ERROR_RELATIVE,PETSC_VIEWER_STDOUT_WORLD));
     94:     PetscCall(PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD));
     95:   }
     96:   PetscCall(EPSDestroy(&eps));
     97:   PetscCall(MatDestroy(&A));
     98:   PetscCall(MatDestroy(&A0));
     99:   PetscCall(SlepcFinalize());
    100:   return 0;
    101: }

    103: /*TEST

    105:    testset:
    106:       args: -eps_nev 4 -terse
    107:       output_file: output/ex46_1.out
    108:       requires: !single
    109:       test:
    110:          suffix: 1
    111:       test:
    112:          suffix: 2
    113:          args: -st_ksp_type bcgs -st_pc_type bjacobi

    115: TEST*/