Actual source code: test3.c
slepc-3.8.2 2017-12-01
1: /*
2: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
3: SLEPc - Scalable Library for Eigenvalue Problem Computations
4: Copyright (c) 2002-2017, 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[] = "Test SVD with user-provided initial vectors.\n\n"
12: "The command line options are:\n"
13: " -n <n>, where <n> = row dimension.\n"
14: " -m <m>, where <m> = column dimension.\n\n";
16: #include <slepcsvd.h>
18: /*
19: This example computes the singular values of a rectangular nxm Grcar matrix:
21: | 1 1 1 1 |
22: | -1 1 1 1 1 |
23: | -1 1 1 1 1 |
24: A = | . . . . . |
25: | . . . . . |
26: | -1 1 1 1 1 |
27: | -1 1 1 1 |
29: */
31: int main(int argc,char **argv)
32: {
33: Mat A; /* Grcar matrix */
34: SVD svd; /* singular value solver context */
35: Vec v0,w0; /* initial vectors */
36: PetscInt N=35,M=30,Istart,Iend,i,col[5];
37: PetscScalar value[] = { -1, 1, 1, 1, 1 };
40: SlepcInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
41: PetscOptionsGetInt(NULL,NULL,"-n",&N,NULL);
42: PetscOptionsGetInt(NULL,NULL,"-m",&M,NULL);
43: PetscPrintf(PETSC_COMM_WORLD,"\nSVD of a rectangular Grcar matrix, %Dx%D\n\n",N,M);
45: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
46: Generate the matrix
47: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
49: MatCreate(PETSC_COMM_WORLD,&A);
50: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,M);
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) {
58: MatSetValues(A,1,&i,PetscMin(4,M-i+1),col+1,value+1,INSERT_VALUES);
59: } else {
60: MatSetValues(A,1,&i,PetscMin(5,M-i+1),col,value,INSERT_VALUES);
61: }
62: }
63: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
64: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
66: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
67: Create the SVD context and solve the problem
68: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
70: SVDCreate(PETSC_COMM_WORLD,&svd);
71: SVDSetOperator(svd,A);
72: SVDSetFromOptions(svd);
74: /*
75: Set the initial vectors. This is optional, if not done the initial
76: vectors are set to random values
77: */
78: MatCreateVecs(A,&v0,&w0);
79: VecSet(v0,1.0);
80: VecSet(w0,1.0);
81: SVDSetInitialSpaces(svd,1,&v0,1,&w0);
83: /*
84: Compute solution
85: */
86: SVDSolve(svd);
87: SVDErrorView(svd,SVD_ERROR_RELATIVE,NULL);
89: /*
90: Free work space
91: */
92: VecDestroy(&v0);
93: VecDestroy(&w0);
94: SVDDestroy(&svd);
95: MatDestroy(&A);
96: SlepcFinalize();
97: return ierr;
98: }