Actual source code: test10.c
slepc-3.17.1 2022-04-11
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[] = "Computes the smallest nonzero eigenvalue of the Laplacian of a graph.\n\n"
12: "This example illustrates EPSSetDeflationSpace(). The example graph corresponds to a "
13: "2-D regular mesh. The command line options are:\n"
14: " -n <n>, where <n> = number of grid subdivisions in x dimension.\n"
15: " -m <m>, where <m> = number of grid subdivisions in y dimension.\n\n";
17: #include <slepceps.h>
19: int main (int argc,char **argv)
20: {
21: EPS eps; /* eigenproblem solver context */
22: Mat A; /* operator matrix */
23: Vec x;
24: PetscInt N,n=10,m,i,j,II,Istart,Iend,nev;
25: PetscScalar w;
26: PetscBool flag;
28: SlepcInitialize(&argc,&argv,(char*)0,help);
30: PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
31: PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag);
32: if (!flag) m=n;
33: N = n*m;
34: PetscPrintf(PETSC_COMM_WORLD,"\nFiedler vector of a 2-D regular mesh, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid)\n\n",N,n,m);
36: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
37: Compute the operator matrix that defines the eigensystem, Ax=kx
38: In this example, A = L(G), where L is the Laplacian of graph G, i.e.
39: Lii = degree of node i, Lij = -1 if edge (i,j) exists in G
40: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
42: MatCreate(PETSC_COMM_WORLD,&A);
43: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);
44: MatSetFromOptions(A);
45: MatSetUp(A);
47: MatGetOwnershipRange(A,&Istart,&Iend);
48: for (II=Istart;II<Iend;II++) {
49: i = II/n; j = II-i*n;
50: w = 0.0;
51: if (i>0) { MatSetValue(A,II,II-n,-1.0,INSERT_VALUES); w=w+1.0; }
52: if (i<m-1) { MatSetValue(A,II,II+n,-1.0,INSERT_VALUES); w=w+1.0; }
53: if (j>0) { MatSetValue(A,II,II-1,-1.0,INSERT_VALUES); w=w+1.0; }
54: if (j<n-1) { MatSetValue(A,II,II+1,-1.0,INSERT_VALUES); w=w+1.0; }
55: MatSetValue(A,II,II,w,INSERT_VALUES);
56: }
58: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
59: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
61: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
62: Create the eigensolver and set various options
63: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
65: /*
66: Create eigensolver context
67: */
68: EPSCreate(PETSC_COMM_WORLD,&eps);
70: /*
71: Set operators. In this case, it is a standard eigenvalue problem
72: */
73: EPSSetOperators(eps,A,NULL);
74: EPSSetProblemType(eps,EPS_HEP);
76: /*
77: Select portion of spectrum
78: */
79: EPSSetWhichEigenpairs(eps,EPS_SMALLEST_REAL);
81: /*
82: Set solver parameters at runtime
83: */
84: EPSSetFromOptions(eps);
86: /*
87: Attach deflation space: in this case, the matrix has a constant
88: nullspace, [1 1 ... 1]^T is the eigenvector of the zero eigenvalue
89: */
90: MatCreateVecs(A,&x,NULL);
91: VecSet(x,1.0);
92: EPSSetDeflationSpace(eps,1,&x);
93: VecDestroy(&x);
95: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
96: Solve the eigensystem
97: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
99: EPSSolve(eps);
100: EPSGetDimensions(eps,&nev,NULL,NULL);
101: PetscPrintf(PETSC_COMM_WORLD," Number of requested eigenvalues: %" PetscInt_FMT "\n",nev);
103: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
104: Display solution and clean up
105: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
107: EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL);
108: EPSDestroy(&eps);
109: MatDestroy(&A);
110: SlepcFinalize();
111: return 0;
112: }
114: /*TEST
116: testset:
117: args: -eps_nev 4 -m 11 -eps_max_it 500
118: output_file: output/test10_1.out
119: test:
120: suffix: 1
121: args: -eps_type {{krylovschur arnoldi gd jd rqcg}}
122: test:
123: suffix: 1_lobpcg
124: args: -eps_type lobpcg -eps_lobpcg_blocksize 6
125: test:
126: suffix: 1_lanczos
127: args: -eps_type lanczos -eps_lanczos_reorthog local
128: requires: !single
129: test:
130: suffix: 1_gd2
131: args: -eps_type gd -eps_gd_double_expansion
133: TEST*/