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

Actual source code: test9.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[] = "Tests multiple calls to SVDSolve with different matrix size.\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,B;
     36:   SVD            svd;
     37:   PetscInt       N=30,Istart,Iend,i,col[5];
     38:   PetscScalar    value[] = { -1, 1, 1, 1, 1 };

     40:   PetscFunctionBeginUser;
     41:   PetscCall(SlepcInitialize(&argc,&argv,NULL,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\n",N));

     45:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     46:         Generate the matrix of size N
     47:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     49:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
     50:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N));
     51:   PetscCall(MatSetFromOptions(A));
     52:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
     53:   for (i=Istart;i<Iend;i++) {
     54:     col[0]=i-1; col[1]=i; col[2]=i+1; col[3]=i+2; col[4]=i+3;
     55:     if (i==0) PetscCall(MatSetValues(A,1,&i,4,col+1,value+1,INSERT_VALUES));
     56:     else PetscCall(MatSetValues(A,1,&i,PetscMin(5,N-i+1),col,value,INSERT_VALUES));
     57:   }
     58:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
     59:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

     61:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     62:          Create the singular value solver, set options and solve
     63:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     65:   PetscCall(SVDCreate(PETSC_COMM_WORLD,&svd));
     66:   PetscCall(SVDSetOperators(svd,A,NULL));
     67:   PetscCall(SVDSetTolerances(svd,1e-6,1000));
     68:   PetscCall(SVDSetFromOptions(svd));
     69:   PetscCall(SVDSolve(svd));
     70:   PetscCall(SVDErrorView(svd,SVD_ERROR_RELATIVE,NULL));

     72:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     73:         Generate the matrix of size 2*N
     74:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     76:   N *= 2;
     77:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\nSingular values of a Grcar matrix, n=%" PetscInt_FMT "\n\n",N));

     79:   PetscCall(MatCreate(PETSC_COMM_WORLD,&B));
     80:   PetscCall(MatSetSizes(B,PETSC_DECIDE,PETSC_DECIDE,N,N));
     81:   PetscCall(MatSetFromOptions(B));
     82:   PetscCall(MatGetOwnershipRange(B,&Istart,&Iend));
     83:   for (i=Istart;i<Iend;i++) {
     84:     col[0]=i-1; col[1]=i; col[2]=i+1; col[3]=i+2; col[4]=i+3;
     85:     if (i==0) PetscCall(MatSetValues(B,1,&i,4,col+1,value+1,INSERT_VALUES));
     86:     else PetscCall(MatSetValues(B,1,&i,PetscMin(5,N-i+1),col,value,INSERT_VALUES));
     87:   }
     88:   PetscCall(MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY));
     89:   PetscCall(MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY));

     91:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     92:        Solve again, calling SVDReset() since matrix size has changed
     93:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     95:   PetscCall(SVDReset(svd));  /* if this is omitted, it will be called in SVDSetOperators() */
     96:   PetscCall(SVDSetOperators(svd,B,NULL));
     97:   PetscCall(SVDSolve(svd));
     98:   PetscCall(SVDErrorView(svd,SVD_ERROR_RELATIVE,NULL));

    100:   /* Free work space */
    101:   PetscCall(SVDDestroy(&svd));
    102:   PetscCall(MatDestroy(&A));
    103:   PetscCall(MatDestroy(&B));
    104:   PetscCall(SlepcFinalize());
    105:   return 0;
    106: }

    108: /*TEST

    110:    test:
    111:       suffix: 1
    112:       args: -svd_type {{lanczos trlanczos cross cyclic lapack randomized}} -svd_nsv 3
    113:       requires: double

    115: TEST*/