Actual source code: test8.c

slepc-3.11.2 2019-07-30
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  1: /*
  2:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  3:    SLEPc - Scalable Library for Eigenvalue Problem Computations
  4:    Copyright (c) 2002-2019, 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 };

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

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

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

 55:   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) {
 59:       MatSetValues(A,1,&i,4,col+1,value+1,INSERT_VALUES);
 60:     } else {
 61:       MatSetValues(A,1,&i,PetscMin(5,N-i+1),col,value,INSERT_VALUES);
 62:     }
 63:   }

 65:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 66:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

 68:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 69:          Create the singular value solver and set the solution method
 70:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 72:   SVDCreate(PETSC_COMM_WORLD,&svd);
 73:   SVDSetOperator(svd,A);
 74:   SVDSetTolerances(svd,1e-6,1000);
 75:   SVDSetWhichSingularTriplets(svd,SVD_LARGEST);
 76:   SVDSetFromOptions(svd);

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

 82:   /* First solve */
 83:   SVDSolve(svd);
 84:   PetscPrintf(PETSC_COMM_WORLD," - - - First solve, default subspace dimension - - -\n");
 85:   SVDErrorView(svd,SVD_ERROR_RELATIVE,NULL);

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

 94:   /* Free work space */
 95:   SVDDestroy(&svd);
 96:   MatDestroy(&A);
 97:   SlepcFinalize();
 98:   return ierr;
 99: }

101: /*TEST

103:    test:
104:       suffix: 1
105:       args: -svd_type {{lanczos trlanczos cross cyclic lapack}} -svd_nsv 3 -svd_ncv 12

107: TEST*/