Actual source code: ex1.c
slepc-3.17.0 2022-03-31
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[] = "Standard symmetric eigenproblem corresponding to the Laplacian operator in 1 dimension.\n\n"
12: "The command line options are:\n"
13: " -n <n>, where <n> = number of grid subdivisions = matrix dimension.\n\n";
15: #include <slepceps.h>
17: int main(int argc,char **argv)
18: {
19: Mat A; /* problem matrix */
20: EPS eps; /* eigenproblem solver context */
21: EPSType type;
22: PetscReal error,tol,re,im;
23: PetscScalar kr,ki;
24: Vec xr,xi;
25: PetscInt n=30,i,Istart,Iend,nev,maxit,its,nconv;
27: SlepcInitialize(&argc,&argv,(char*)0,help);
29: PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
30: PetscPrintf(PETSC_COMM_WORLD,"\n1-D Laplacian Eigenproblem, n=%" PetscInt_FMT "\n\n",n);
32: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
33: Compute the operator matrix that defines the eigensystem, Ax=kx
34: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
36: MatCreate(PETSC_COMM_WORLD,&A);
37: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n,n);
38: MatSetFromOptions(A);
39: MatSetUp(A);
41: MatGetOwnershipRange(A,&Istart,&Iend);
42: for (i=Istart;i<Iend;i++) {
43: if (i>0) MatSetValue(A,i,i-1,-1.0,INSERT_VALUES);
44: if (i<n-1) MatSetValue(A,i,i+1,-1.0,INSERT_VALUES);
45: MatSetValue(A,i,i,2.0,INSERT_VALUES);
46: }
47: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
48: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
50: MatCreateVecs(A,NULL,&xr);
51: MatCreateVecs(A,NULL,&xi);
53: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
54: Create the eigensolver and set various options
55: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
56: /*
57: Create eigensolver context
58: */
59: EPSCreate(PETSC_COMM_WORLD,&eps);
61: /*
62: Set operators. In this case, it is a standard eigenvalue problem
63: */
64: EPSSetOperators(eps,A,NULL);
65: EPSSetProblemType(eps,EPS_HEP);
67: /*
68: Set solver parameters at runtime
69: */
70: EPSSetFromOptions(eps);
72: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73: Solve the eigensystem
74: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
76: EPSSolve(eps);
77: /*
78: Optional: Get some information from the solver and display it
79: */
80: EPSGetIterationNumber(eps,&its);
81: PetscPrintf(PETSC_COMM_WORLD," Number of iterations of the method: %" PetscInt_FMT "\n",its);
82: EPSGetType(eps,&type);
83: PetscPrintf(PETSC_COMM_WORLD," Solution method: %s\n\n",type);
84: EPSGetDimensions(eps,&nev,NULL,NULL);
85: PetscPrintf(PETSC_COMM_WORLD," Number of requested eigenvalues: %" PetscInt_FMT "\n",nev);
86: EPSGetTolerances(eps,&tol,&maxit);
87: PetscPrintf(PETSC_COMM_WORLD," Stopping condition: tol=%.4g, maxit=%" PetscInt_FMT "\n",(double)tol,maxit);
89: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
90: Display solution and clean up
91: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
92: /*
93: Get number of converged approximate eigenpairs
94: */
95: EPSGetConverged(eps,&nconv);
96: PetscPrintf(PETSC_COMM_WORLD," Number of converged eigenpairs: %" PetscInt_FMT "\n\n",nconv);
98: if (nconv>0) {
99: /*
100: Display eigenvalues and relative errors
101: */
102: PetscCall(PetscPrintf(PETSC_COMM_WORLD,
103: " k ||Ax-kx||/||kx||\n"
104: " ----------------- ------------------\n"));
106: for (i=0;i<nconv;i++) {
107: /*
108: Get converged eigenpairs: i-th eigenvalue is stored in kr (real part) and
109: ki (imaginary part)
110: */
111: EPSGetEigenpair(eps,i,&kr,&ki,xr,xi);
112: /*
113: Compute the relative error associated to each eigenpair
114: */
115: EPSComputeError(eps,i,EPS_ERROR_RELATIVE,&error);
117: #if defined(PETSC_USE_COMPLEX)
118: re = PetscRealPart(kr);
119: im = PetscImaginaryPart(kr);
120: #else
121: re = kr;
122: im = ki;
123: #endif
124: if (im!=0.0) PetscPrintf(PETSC_COMM_WORLD," %9f%+9fi %12g\n",(double)re,(double)im,(double)error);
125: else PetscPrintf(PETSC_COMM_WORLD," %12f %12g\n",(double)re,(double)error);
126: }
127: PetscPrintf(PETSC_COMM_WORLD,"\n");
128: }
130: /*
131: Free work space
132: */
133: EPSDestroy(&eps);
134: MatDestroy(&A);
135: VecDestroy(&xr);
136: VecDestroy(&xi);
137: SlepcFinalize();
138: return 0;
139: }