Actual source code: ex15.c
1: /*
2: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
3: SLEPc - Scalable Library for Eigenvalue Problem Computations
4: Copyright (c) 2002-2009, Universidad Politecnica de Valencia, Spain
6: This file is part of SLEPc.
7:
8: SLEPc is free software: you can redistribute it and/or modify it under the
9: terms of version 3 of the GNU Lesser General Public License as published by
10: the Free Software Foundation.
12: SLEPc is distributed in the hope that it will be useful, but WITHOUT ANY
13: WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
14: FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
15: more details.
17: You should have received a copy of the GNU Lesser General Public License
18: along with SLEPc. If not, see <http://www.gnu.org/licenses/>.
19: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
20: */
22: static char help[] = "Singular value decomposition of the Lauchli matrix.\n"
23: "The command line options are:\n"
24: " -n <n>, where <n> = matrix dimension.\n"
25: " -mu <mu>, where <mu> = subdiagonal value.\n\n";
27: #include slepcsvd.h
31: int main( int argc, char **argv )
32: {
33: Mat A; /* operator matrix */
34: SVD svd; /* singular value problem solver context */
35: const SVDType type;
36: PetscReal error, tol, sigma, mu=PETSC_SQRT_MACHINE_EPSILON;
38: PetscInt n=100, i, j, Istart, Iend, nsv, maxit, its, nconv;
40: SlepcInitialize(&argc,&argv,(char*)0,help);
42: PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);
43: PetscOptionsGetReal(PETSC_NULL,"-mu",&mu,PETSC_NULL);
44: PetscPrintf(PETSC_COMM_WORLD,"\nLauchli singular value decomposition, (%d x %d) mu=%g\n\n",n+1,n,mu);
46: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
47: Build the Lauchli matrix
48: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
50: MatCreate(PETSC_COMM_WORLD,&A);
51: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n+1,n);
52: MatSetFromOptions(A);
54: MatGetOwnershipRange(A,&Istart,&Iend);
55: for (i=Istart;i<Iend;i++) {
56: if (i == 0) {
57: for (j=0;j<n;j++) {
58: MatSetValue(A,0,j,1.0,INSERT_VALUES);
59: }
60: } else {
61: MatSetValue(A,i,i-1,mu,INSERT_VALUES);
62: }
63: }
64:
65: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
66: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
68: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
69: Create the singular value solver and set various options
70: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
72: /*
73: Create singular value solver context
74: */
75: SVDCreate(PETSC_COMM_WORLD,&svd);
77: /*
78: Set operator
79: */
80: SVDSetOperator(svd,A);
81:
82: /*
83: Use thick-restart Lanczos as default solver
84: */
85: SVDSetType(svd,SVDTRLANCZOS);
87: /*
88: Set solver parameters at runtime
89: */
90: SVDSetFromOptions(svd);
92: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
93: Solve the singular value system
94: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
96: SVDSolve(svd);
97: SVDGetIterationNumber(svd, &its);
98: PetscPrintf(PETSC_COMM_WORLD," Number of iterations of the method: %d\n",its);
100: /*
101: Optional: Get some information from the solver and display it
102: */
103: SVDGetType(svd,&type);
104: PetscPrintf(PETSC_COMM_WORLD," Solution method: %s\n\n",type);
105: SVDGetDimensions(svd,&nsv,PETSC_NULL,PETSC_NULL);
106: PetscPrintf(PETSC_COMM_WORLD," Number of requested singular values: %d\n",nsv);
107: SVDGetTolerances(svd,&tol,&maxit);
108: PetscPrintf(PETSC_COMM_WORLD," Stopping condition: tol=%.4g, maxit=%d\n",tol,maxit);
110: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
111: Display solution and clean up
112: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
114: /*
115: Get number of converged singular triplets
116: */
117: SVDGetConverged(svd,&nconv);
118: PetscPrintf(PETSC_COMM_WORLD," Number of converged approximate singular triplets: %d\n\n",nconv);
120: if (nconv>0) {
121: /*
122: Display singular values and relative errors
123: */
124: PetscPrintf(PETSC_COMM_WORLD,
125: " sigma residual norm\n"
126: " --------------------- ------------------\n" );
127: for( i=0; i<nconv; i++ ) {
128: /*
129: Get converged singular triplets: i-th singular value is stored in sigma
130: */
131: SVDGetSingularTriplet(svd,i,&sigma,PETSC_NULL,PETSC_NULL);
133: /*
134: Compute the error associated to each singular triplet
135: */
136: SVDComputeRelativeError(svd,i,&error);
138: PetscPrintf(PETSC_COMM_WORLD," % 6f ",sigma);
139: PetscPrintf(PETSC_COMM_WORLD," % 12g\n",error);
140: }
141: PetscPrintf(PETSC_COMM_WORLD,"\n" );
142: }
143:
144: /*
145: Free work space
146: */
147: SVDDestroy(svd);
148: MatDestroy(A);
149: SlepcFinalize();
150: return 0;
151: }