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*/