Date: 2022-03-31T15:29:22+00:00

Actual source code: test8.c
slepc-3.17.0 2022-03-31
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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:   SlepcInitialize(&argc,&argv,(char*)0,help);
     41:   PetscOptionsGetInt(NULL,NULL,"-n",&N,NULL);
     42:   PetscPrintf(PETSC_COMM_WORLD,"\nSingular values of a Grcar matrix, n=%" PetscInt_FMT,N);
     43:   PetscPrintf(PETSC_COMM_WORLD,"\n\n");

     45:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     46:         Generate the matrix
     47:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

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

     61:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
     62:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

     64:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     65:          Create the singular value solver and set the solution method
     66:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

     74:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     75:                       Compute the singular values
     76:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

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

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

     97: /*TEST

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

    104: TEST*/