Actual source code: spring.c
slepc-3.5.2 2014-10-10
1: /*
2: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
3: SLEPc - Scalable Library for Eigenvalue Problem Computations
4: Copyright (c) 2002-2014, Universitat Politecnica de Valencia, Spain
6: This file is part of SLEPc.
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: */
21: /*
22: This example implements one of the problems found at
23: NLEVP: A Collection of Nonlinear Eigenvalue Problems,
24: The University of Manchester.
25: The details of the collection can be found at:
26: [1] T. Betcke et al., "NLEVP: A Collection of Nonlinear Eigenvalue
27: Problems", ACM Trans. Math. Software 39(2), Article 7, 2013.
29: The spring problem is a QEP from the finite element model of a damped
30: mass-spring system. This implementation supports only scalar parameters,
31: that is all masses, dampers and springs have the same constants.
32: Furthermore, this implementation does not consider different constants
33: for dampers and springs connecting adjacent masses or masses to the ground.
34: */
36: static char help[] = "NLEVP problem: spring.\n\n"
37: "The command line options are:\n"
38: " -n <n> ... dimension of the matrices.\n"
39: " -mu <value> ... mass (default 1).\n"
40: " -tau <value> ... damping constant of the dampers (default 10).\n"
41: " -kappa <value> ... damping constant of the springs (default 5).\n\n";
43: #include <slepcpep.h>
47: int main(int argc,char **argv)
48: {
49: Mat M,C,K,A[3]; /* problem matrices */
50: PEP pep; /* polynomial eigenproblem solver context */
51: PetscInt n=5,Istart,Iend,i;
52: PetscReal mu=1,tau=10,kappa=5;
55: SlepcInitialize(&argc,&argv,(char*)0,help);
57: PetscOptionsGetInt(NULL,"-n",&n,NULL);
58: PetscOptionsGetReal(NULL,"-mu",&mu,NULL);
59: PetscOptionsGetReal(NULL,"-tau",&tau,NULL);
60: PetscOptionsGetReal(NULL,"-kappa",&kappa,NULL);
61: PetscPrintf(PETSC_COMM_WORLD,"\nDamped mass-spring system, n=%D mu=%g tau=%g kappa=%g\n\n",n,(double)mu,(double)tau,(double)kappa);
63: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
64: Compute the matrices that define the eigensystem, (k^2*M+k*C+K)x=0
65: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
67: /* K is a tridiagonal */
68: MatCreate(PETSC_COMM_WORLD,&K);
69: MatSetSizes(K,PETSC_DECIDE,PETSC_DECIDE,n,n);
70: MatSetFromOptions(K);
71: MatSetUp(K);
72:
73: MatGetOwnershipRange(K,&Istart,&Iend);
74: for (i=Istart;i<Iend;i++) {
75: if (i>0) {
76: MatSetValue(K,i,i-1,-kappa,INSERT_VALUES);
77: }
78: MatSetValue(K,i,i,kappa*3.0,INSERT_VALUES);
79: if (i<n-1) {
80: MatSetValue(K,i,i+1,-kappa,INSERT_VALUES);
81: }
82: }
84: MatAssemblyBegin(K,MAT_FINAL_ASSEMBLY);
85: MatAssemblyEnd(K,MAT_FINAL_ASSEMBLY);
87: /* C is a tridiagonal */
88: MatCreate(PETSC_COMM_WORLD,&C);
89: MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,n,n);
90: MatSetFromOptions(C);
91: MatSetUp(C);
92:
93: MatGetOwnershipRange(C,&Istart,&Iend);
94: for (i=Istart;i<Iend;i++) {
95: if (i>0) {
96: MatSetValue(C,i,i-1,-tau,INSERT_VALUES);
97: }
98: MatSetValue(C,i,i,tau*3.0,INSERT_VALUES);
99: if (i<n-1) {
100: MatSetValue(C,i,i+1,-tau,INSERT_VALUES);
101: }
102: }
104: MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
105: MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
106:
107: /* M is a diagonal matrix */
108: MatCreate(PETSC_COMM_WORLD,&M);
109: MatSetSizes(M,PETSC_DECIDE,PETSC_DECIDE,n,n);
110: MatSetFromOptions(M);
111: MatSetUp(M);
112: MatAssemblyBegin(M,MAT_FINAL_ASSEMBLY);
113: MatAssemblyEnd(M,MAT_FINAL_ASSEMBLY);
114: MatShift(M,mu);
116: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
117: Create the eigensolver and solve the problem
118: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
120: PEPCreate(PETSC_COMM_WORLD,&pep);
121: A[0] = K; A[1] = C; A[2] = M;
122: PEPSetOperators(pep,3,A);
123: PEPSetFromOptions(pep);
124: PEPSolve(pep);
126: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
127: Display solution and clean up
128: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
129:
130: PEPPrintSolution(pep,NULL);
131: PEPDestroy(&pep);
132: MatDestroy(&M);
133: MatDestroy(&C);
134: MatDestroy(&K);
135: SlepcFinalize();
136: return 0;
137: }