Actual source code: ex2.c

  1: /*
  2:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  3:    SLEPc - Scalable Library for Eigenvalue Problem Computations
  4:    Copyright (c) 2002-2013, 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: */

 22: static char help[] = "Standard symmetric eigenproblem corresponding to the Laplacian operator in 2 dimensions.\n\n"
 23:   "The command line options are:\n"
 24:   "  -n <n>, where <n> = number of grid subdivisions in x dimension.\n"
 25:   "  -m <m>, where <m> = number of grid subdivisions in y dimension.\n\n";

 27: #include <slepceps.h>

 31: int main(int argc,char **argv)
 32: {
 33:   Mat            A;               /* operator matrix */
 34:   EPS            eps;             /* eigenproblem solver context */
 35:   EPSType        type;
 36:   PetscInt       N,n=10,m,Istart,Iend,II,nev,i,j;
 37:   PetscBool      flag;

 40:   SlepcInitialize(&argc,&argv,(char*)0,help);

 42:   PetscOptionsGetInt(NULL,"-n",&n,NULL);
 43:   PetscOptionsGetInt(NULL,"-m",&m,&flag);
 44:   if (!flag) m=n;
 45:   N = n*m;
 46:   PetscPrintf(PETSC_COMM_WORLD,"\n2-D Laplacian Eigenproblem, N=%D (%Dx%D grid)\n\n",N,n,m);

 48:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 49:      Compute the operator matrix that defines the eigensystem, Ax=kx
 50:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 52:   MatCreate(PETSC_COMM_WORLD,&A);
 53:   MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);
 54:   MatSetFromOptions(A);
 55:   MatSetUp(A);

 57:   MatGetOwnershipRange(A,&Istart,&Iend);
 58:   for (II=Istart;II<Iend;II++) {
 59:     i = II/n; j = II-i*n;
 60:     if (i>0) { MatSetValue(A,II,II-n,-1.0,INSERT_VALUES); }
 61:     if (i<m-1) { MatSetValue(A,II,II+n,-1.0,INSERT_VALUES); }
 62:     if (j>0) { MatSetValue(A,II,II-1,-1.0,INSERT_VALUES); }
 63:     if (j<n-1) { MatSetValue(A,II,II+1,-1.0,INSERT_VALUES); }
 64:     MatSetValue(A,II,II,4.0,INSERT_VALUES);
 65:   }

 67:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 68:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

 70:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 71:                 Create the eigensolver and set various options
 72:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 74:   /*
 75:      Create eigensolver context
 76:   */
 77:   EPSCreate(PETSC_COMM_WORLD,&eps);

 79:   /*
 80:      Set operators. In this case, it is a standard eigenvalue problem
 81:   */
 82:   EPSSetOperators(eps,A,NULL);
 83:   EPSSetProblemType(eps,EPS_HEP);

 85:   /*
 86:      Set solver parameters at runtime
 87:   */
 88:   EPSSetFromOptions(eps);

 90:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 91:                       Solve the eigensystem
 92:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 94:   EPSSolve(eps);

 96:   /*
 97:      Optional: Get some information from the solver and display it
 98:   */
 99:   EPSGetType(eps,&type);
100:   PetscPrintf(PETSC_COMM_WORLD," Solution method: %s\n\n",type);
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:   EPSPrintSolution(eps,NULL);
109:   EPSDestroy(&eps);
110:   MatDestroy(&A);
111:   SlepcFinalize();
112:   return 0;
113: }