Date: 2026-03-31T13:23:07+00:00

Actual source code: test6.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[] = "SVD via the cross-product matrix with a user-provided EPS.\n\n"
     12:   "The command line options are:\n"
     13:   "  -m <m>, where <m> = matrix rows.\n"
     14:   "  -n <n>, where <n> = matrix columns (defaults to m+2).\n\n";

     16: #include <slepcsvd.h>

     18: /*
     19:    This example computes the singular values of a rectangular bidiagonal matrix

     21:               |  1  2                     |
     22:               |     1  2                  |
     23:               |        1  2               |
     24:           A = |          .  .             |
     25:               |             .  .          |
     26:               |                1  2       |
     27:               |                   1  2    |
     28:  */

     30: int main(int argc,char **argv)
     31: {
     32:   Mat            A;
     33:   SVD            svd;
     34:   EPS            eps;
     35:   ST             st;
     36:   KSP            ksp;
     37:   PC             pc;
     38:   PetscInt       m=20,n,Istart,Iend,i,col[2];
     39:   PetscScalar    value[] = { 1, 2 };
     40:   PetscBool      flg,expmat;

     42:   PetscFunctionBeginUser;
     43:   PetscCall(SlepcInitialize(&argc,&argv,NULL,help));
     44:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-m",&m,NULL));
     45:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,&flg));
     46:   if (!flg) n=m+2;
     47:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\nRectangular bidiagonal matrix, m=%" PetscInt_FMT " n=%" PetscInt_FMT "\n\n",m,n));

     49:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     50:         Generate the matrix
     51:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     53:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
     54:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m,n));
     55:   PetscCall(MatSetFromOptions(A));
     56:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
     57:   for (i=Istart;i<Iend;i++) {
     58:     col[0]=i; col[1]=i+1;
     59:     if (i<n-1) PetscCall(MatSetValues(A,1,&i,2,col,value,INSERT_VALUES));
     60:     else if (i==n-1) PetscCall(MatSetValue(A,i,col[0],value[0],INSERT_VALUES));
     61:   }
     62:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
     63:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

     65:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     66:         Create a standalone EPS with appropriate settings
     67:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     69:   PetscCall(EPSCreate(PETSC_COMM_WORLD,&eps));
     70:   PetscCall(EPSGetST(eps,&st));
     71:   PetscCall(STSetType(st,STSINVERT));
     72:   PetscCall(STGetKSP(st,&ksp));
     73:   PetscCall(KSPSetType(ksp,KSPBCGS));
     74:   PetscCall(KSPGetPC(ksp,&pc));
     75:   PetscCall(PCSetType(pc,PCJACOBI));
     76:   PetscCall(EPSSetFromOptions(eps));

     78:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     79:         Compute singular values
     80:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     82:   PetscCall(SVDCreate(PETSC_COMM_WORLD,&svd));
     83:   PetscCall(SVDSetOperators(svd,A,NULL));
     84:   PetscCall(SVDSetType(svd,SVDCROSS));
     85:   PetscCall(SVDCrossSetEPS(svd,eps));
     86:   PetscCall(SVDSetWhichSingularTriplets(svd,SVD_SMALLEST));
     87:   PetscCall(SVDSetFromOptions(svd));
     88:   PetscCall(PetscObjectTypeCompare((PetscObject)svd,SVDCROSS,&flg));
     89:   if (flg) {
     90:     PetscCall(SVDCrossGetExplicitMatrix(svd,&expmat));
     91:     if (expmat) PetscCall(PetscPrintf(PETSC_COMM_WORLD," Using explicit matrix with cross solver\n"));
     92:   }
     93:   PetscCall(SVDSolve(svd));

     95:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     96:                     Display solution and clean up
     97:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
     98:   PetscCall(SVDErrorView(svd,SVD_ERROR_NORM,PETSC_VIEWER_STDOUT_WORLD));
     99:   PetscCall(SVDDestroy(&svd));
    100:   PetscCall(EPSDestroy(&eps));
    101:   PetscCall(MatDestroy(&A));
    102:   PetscCall(SlepcFinalize());
    103:   return 0;
    104: }

    106: /*TEST

    108:    testset:
    109:       output_file: output/test6_1.out
    110:       test:
    111:          suffix: 1_subspace
    112:          args: -eps_type subspace
    113:       test:
    114:          suffix: 1_lobpcg
    115:          args: -eps_type lobpcg -st_type precond
    116:       test:
    117:          suffix: 2_cuda
    118:          args: -eps_type subspace -mat_type aijcusparse
    119:          requires: cuda
    120:       test:
    121:          suffix: 2_hip
    122:          args: -eps_type subspace -mat_type aijhipsparse
    123:          requires: hip

    125: TEST*/