Date: 2026-05-01T10:02:09+00:00

Actual source code: test10.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[] = "Lanczos SVD. Also illustrates the use of SVDSetBV().\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:   PetscInt       m=20,n,Istart,Iend,i,k=6,col[2];
     35:   PetscScalar    value[] = { 1, 2 };
     36:   PetscBool      flg,oneside=PETSC_FALSE;
     37:   const char     *prefix;
     38:   BV             U,V;
     39:   Vec            u,v;

     41:   PetscFunctionBeginUser;
     42:   PetscCall(SlepcInitialize(&argc,&argv,NULL,help));
     43:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-m",&m,NULL));
     44:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,&flg));
     45:   if (!flg) n=m+2;
     46:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-k",&k,NULL));
     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));
     64:   PetscCall(MatCreateVecs(A,&v,&u));

     66:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     67:          Create standalone BV objects to illustrate use of SVDSetBV()
     68:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     70:   PetscCall(BVCreate(PETSC_COMM_WORLD,&U));
     71:   PetscCall(PetscObjectSetName((PetscObject)U,"U"));
     72:   PetscCall(BVSetSizesFromVec(U,u,k));
     73:   PetscCall(BVSetFromOptions(U));
     74:   PetscCall(BVCreate(PETSC_COMM_WORLD,&V));
     75:   PetscCall(PetscObjectSetName((PetscObject)V,"V"));
     76:   PetscCall(BVSetSizesFromVec(V,v,k));
     77:   PetscCall(BVSetFromOptions(V));

     79:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     80:         Compute singular values
     81:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     83:   PetscCall(SVDCreate(PETSC_COMM_WORLD,&svd));
     84:   PetscCall(SVDSetBV(svd,V,U));
     85:   PetscCall(SVDSetOptionsPrefix(svd,"check_"));
     86:   PetscCall(SVDAppendOptionsPrefix(svd,"myprefix_"));
     87:   PetscCall(SVDGetOptionsPrefix(svd,&prefix));
     88:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"SVD prefix is currently: %s\n\n",prefix));
     89:   PetscCall(PetscObjectSetName((PetscObject)svd,"SVD_solver"));

     91:   PetscCall(SVDSetOperators(svd,A,NULL));
     92:   PetscCall(SVDSetType(svd,SVDLANCZOS));
     93:   PetscCall(SVDSetFromOptions(svd));

     95:   PetscCall(PetscObjectTypeCompare((PetscObject)svd,SVDLANCZOS,&flg));
     96:   if (flg) {
     97:     PetscCall(SVDLanczosGetOneSide(svd,&oneside));
     98:     PetscCall(PetscPrintf(PETSC_COMM_WORLD,"Running Lanczos %s\n\n",oneside?"(onesided)":""));
     99:   }
    100:   PetscCall(PetscObjectTypeCompare((PetscObject)svd,SVDTRLANCZOS,&flg));
    101:   if (flg) {
    102:     PetscCall(SVDTRLanczosGetOneSide(svd,&oneside));
    103:     PetscCall(PetscPrintf(PETSC_COMM_WORLD,"Running thick-restart Lanczos %s\n\n",oneside?"(onesided)":""));
    104:   }

    106:   PetscCall(SVDSolve(svd));

    108:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    109:                     Display solution and clean up
    110:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    111:   PetscCall(SVDErrorView(svd,SVD_ERROR_RELATIVE,PETSC_VIEWER_STDOUT_WORLD));
    112:   PetscCall(BVDestroy(&U));
    113:   PetscCall(BVDestroy(&V));
    114:   PetscCall(VecDestroy(&u));
    115:   PetscCall(VecDestroy(&v));
    116:   PetscCall(SVDDestroy(&svd));
    117:   PetscCall(MatDestroy(&A));
    118:   PetscCall(SlepcFinalize());
    119:   return 0;
    120: }

    122: /*TEST

    124:    testset:
    125:       args: -check_myprefix_svd_nsv 3
    126:       requires: double
    127:       test:
    128:          suffix: 1
    129:          args: -check_myprefix_svd_view_vectors ::ascii_info
    130:       test:
    131:          suffix: 2
    132:          args: -check_myprefix_svd_type trlanczos -check_myprefix_svd_monitor -check_myprefix_svd_view_values ::ascii_matlab
    133:          filter: sed -e "s/[0-9]\.[0-9]*e[+-]\([0-9]*\)/removed/g"
    134:       test:
    135:          suffix: 3
    136:          args: -m 22 -n 20

    138: TEST*/