Date: 2023-09-05T10:18:42+00:00

Actual source code: test8.c
slepc-3.19.2 2023-09-05
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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[] = "Tests multiple calls to SVDSolve changing ncv.\n\n"
     12:   "The command line options are:\n"
     13:   "  -n <n>, where <n> = matrix dimension.\n\n";

     15: #include <slepcsvd.h>

     17: /*
     18:    This example computes the singular values of an nxn Grcar matrix,
     19:    which is a nonsymmetric Toeplitz matrix:

     21:               |  1  1  1  1               |
     22:               | -1  1  1  1  1            |
     23:               |    -1  1  1  1  1         |
     24:               |       .  .  .  .  .       |
     25:           A = |          .  .  .  .  .    |
     26:               |            -1  1  1  1  1 |
     27:               |               -1  1  1  1 |
     28:               |                  -1  1  1 |
     29:               |                     -1  1 |

     31:  */

     33: int main(int argc,char **argv)
     34: {
     35:   Mat            A;
     36:   SVD            svd;
     37:   PetscInt       N=30,Istart,Iend,i,col[5],nsv,ncv;
     38:   PetscScalar    value[] = { -1, 1, 1, 1, 1 };

     40:   PetscFunctionBeginUser;
     41:   PetscCall(SlepcInitialize(&argc,&argv,(char*)0,help));
     42:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&N,NULL));
     43:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\nSingular values of a Grcar matrix, n=%" PetscInt_FMT,N));
     44:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\n\n"));

     46:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     47:         Generate the matrix
     48:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     50:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
     51:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N));
     52:   PetscCall(MatSetFromOptions(A));
     53:   PetscCall(MatSetUp(A));

     55:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
     56:   for (i=Istart;i<Iend;i++) {
     57:     col[0]=i-1; col[1]=i; col[2]=i+1; col[3]=i+2; col[4]=i+3;
     58:     if (i==0) PetscCall(MatSetValues(A,1,&i,4,col+1,value+1,INSERT_VALUES));
     59:     else PetscCall(MatSetValues(A,1,&i,PetscMin(5,N-i+1),col,value,INSERT_VALUES));
     60:   }

     62:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
     63:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

     65:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     66:          Create the singular value solver and set the solution method
     67:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     69:   PetscCall(SVDCreate(PETSC_COMM_WORLD,&svd));
     70:   PetscCall(SVDSetOperators(svd,A,NULL));
     71:   PetscCall(SVDSetTolerances(svd,1e-6,1000));
     72:   PetscCall(SVDSetWhichSingularTriplets(svd,SVD_LARGEST));
     73:   PetscCall(SVDSetFromOptions(svd));

     75:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     76:                       Compute the singular values
     77:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     79:   /* First solve */
     80:   PetscCall(SVDSolve(svd));
     81:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," - - - First solve, default subspace dimension - - -\n"));
     82:   PetscCall(SVDErrorView(svd,SVD_ERROR_RELATIVE,NULL));

     84:   /* Second solve */
     85:   PetscCall(SVDGetDimensions(svd,&nsv,&ncv,NULL));
     86:   PetscCall(SVDSetDimensions(svd,nsv,ncv+2,PETSC_DEFAULT));
     87:   PetscCall(SVDSolve(svd));
     88:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," - - - Second solve, subspace of increased size - - -\n"));
     89:   PetscCall(SVDErrorView(svd,SVD_ERROR_RELATIVE,NULL));

     91:   /* Free work space */
     92:   PetscCall(SVDDestroy(&svd));
     93:   PetscCall(MatDestroy(&A));
     94:   PetscCall(SlepcFinalize());
     95:   return 0;
     96: }

     98: /*TEST

    100:    test:
    101:       suffix: 1
    102:       args: -svd_type {{lanczos trlanczos cross cyclic lapack randomized}} -svd_nsv 3 -svd_ncv 12
    103:       requires: !single

    105: TEST*/