Actual source code: test10.c
slepc-3.11.2 2019-07-30
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[] = "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;
29: SlepcInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
31: PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
32: PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag);
33: if (!flag) m=n;
34: N = n*m;
35: PetscPrintf(PETSC_COMM_WORLD,"\nFiedler vector of a 2-D regular mesh, N=%D (%Dx%D grid)\n\n",N,n,m);
37: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
38: Compute the operator matrix that defines the eigensystem, Ax=kx
39: In this example, A = L(G), where L is the Laplacian of graph G, i.e.
40: Lii = degree of node i, Lij = -1 if edge (i,j) exists in G
41: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
43: MatCreate(PETSC_COMM_WORLD,&A);
44: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);
45: MatSetFromOptions(A);
46: MatSetUp(A);
48: MatGetOwnershipRange(A,&Istart,&Iend);
49: for (II=Istart;II<Iend;II++) {
50: i = II/n; j = II-i*n;
51: w = 0.0;
52: if (i>0) { MatSetValue(A,II,II-n,-1.0,INSERT_VALUES); w=w+1.0; }
53: if (i<m-1) { MatSetValue(A,II,II+n,-1.0,INSERT_VALUES); w=w+1.0; }
54: if (j>0) { MatSetValue(A,II,II-1,-1.0,INSERT_VALUES); w=w+1.0; }
55: if (j<n-1) { MatSetValue(A,II,II+1,-1.0,INSERT_VALUES); w=w+1.0; }
56: MatSetValue(A,II,II,w,INSERT_VALUES);
57: }
59: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
60: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
62: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
63: Create the eigensolver and set various options
64: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
66: /*
67: Create eigensolver context
68: */
69: EPSCreate(PETSC_COMM_WORLD,&eps);
71: /*
72: Set operators. In this case, it is a standard eigenvalue problem
73: */
74: EPSSetOperators(eps,A,NULL);
75: EPSSetProblemType(eps,EPS_HEP);
77: /*
78: Select portion of spectrum
79: */
80: EPSSetWhichEigenpairs(eps,EPS_SMALLEST_REAL);
82: /*
83: Set solver parameters at runtime
84: */
85: EPSSetFromOptions(eps);
87: /*
88: Attach deflation space: in this case, the matrix has a constant
89: nullspace, [1 1 ... 1]^T is the eigenvector of the zero eigenvalue
90: */
91: MatCreateVecs(A,&x,NULL);
92: VecSet(x,1.0);
93: EPSSetDeflationSpace(eps,1,&x);
94: VecDestroy(&x);
96: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
97: Solve the eigensystem
98: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
100: EPSSolve(eps);
101: EPSGetDimensions(eps,&nev,NULL,NULL);
102: PetscPrintf(PETSC_COMM_WORLD," Number of requested eigenvalues: %D\n",nev);
104: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
105: Display solution and clean up
106: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
108: EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL);
109: EPSDestroy(&eps);
110: MatDestroy(&A);
111: SlepcFinalize();
112: return ierr;
113: }
115: /*TEST
117: testset:
118: args: -eps_nev 4 -m 11 -eps_max_it 500
119: requires: !single
120: output_file: output/test10_1.out
121: test:
122: suffix: 1
123: args: -eps_type {{krylovschur arnoldi lanczos gd jd rqcg lobpcg}}
124: test:
125: suffix: 1_gd2
126: args: -eps_type gd -eps_gd_double_expansion
128: TEST*/