Actual source code: test8.c
slepc-3.17.2 2022-08-09
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*/