Actual source code: ex1.c

slepc-3.6.3 2016-03-29
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  1: /*
  2:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  3:    SLEPc - Scalable Library for Eigenvalue Problem Computations
  4:    Copyright (c) 2002-2015, 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 1 dimension.\n\n"
 23:   "The command line options are:\n"
 24:   "  -n <n>, where <n> = number of grid subdivisions = matrix dimension.\n\n";

 26: #include <slepceps.h>

 30: int main(int argc,char **argv)
 31: {
 32:   Mat            A;           /* problem matrix */
 33:   EPS            eps;         /* eigenproblem solver context */
 34:   EPSType        type;
 35:   PetscReal      error,tol,re,im;
 36:   PetscScalar    kr,ki;
 37:   Vec            xr,xi;
 38:   PetscInt       n=30,i,Istart,Iend,nev,maxit,its,nconv;

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

 43:   PetscOptionsGetInt(NULL,"-n",&n,NULL);
 44:   PetscPrintf(PETSC_COMM_WORLD,"\n1-D Laplacian Eigenproblem, n=%D\n\n",n);

 46:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 47:      Compute the operator matrix that defines the eigensystem, Ax=kx
 48:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 50:   MatCreate(PETSC_COMM_WORLD,&A);
 51:   MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n,n);
 52:   MatSetFromOptions(A);
 53:   MatSetUp(A);

 55:   MatGetOwnershipRange(A,&Istart,&Iend);
 56:   for (i=Istart;i<Iend;i++) {
 57:     if (i>0) { MatSetValue(A,i,i-1,-1.0,INSERT_VALUES); }
 58:     if (i<n-1) { MatSetValue(A,i,i+1,-1.0,INSERT_VALUES); }
 59:     MatSetValue(A,i,i,2.0,INSERT_VALUES);
 60:   }
 61:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 62:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

 64:   MatCreateVecs(A,NULL,&xr);
 65:   MatCreateVecs(A,NULL,&xi);

 67:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 68:                 Create the eigensolver and set various options
 69:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 70:   /*
 71:      Create eigensolver context
 72:   */
 73:   EPSCreate(PETSC_COMM_WORLD,&eps);

 75:   /*
 76:      Set operators. In this case, it is a standard eigenvalue problem
 77:   */
 78:   EPSSetOperators(eps,A,NULL);
 79:   EPSSetProblemType(eps,EPS_HEP);

 81:   /*
 82:      Set solver parameters at runtime
 83:   */
 84:   EPSSetFromOptions(eps);

 86:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 87:                       Solve the eigensystem
 88:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

 90:   EPSSolve(eps);
 91:   /*
 92:      Optional: Get some information from the solver and display it
 93:   */
 94:   EPSGetIterationNumber(eps,&its);
 95:   PetscPrintf(PETSC_COMM_WORLD," Number of iterations of the method: %D\n",its);
 96:   EPSGetType(eps,&type);
 97:   PetscPrintf(PETSC_COMM_WORLD," Solution method: %s\n\n",type);
 98:   EPSGetDimensions(eps,&nev,NULL,NULL);
 99:   PetscPrintf(PETSC_COMM_WORLD," Number of requested eigenvalues: %D\n",nev);
100:   EPSGetTolerances(eps,&tol,&maxit);
101:   PetscPrintf(PETSC_COMM_WORLD," Stopping condition: tol=%.4g, maxit=%D\n",(double)tol,maxit);

103:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
104:                     Display solution and clean up
105:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
106:   /*
107:      Get number of converged approximate eigenpairs
108:   */
109:   EPSGetConverged(eps,&nconv);
110:   PetscPrintf(PETSC_COMM_WORLD," Number of converged eigenpairs: %D\n\n",nconv);

112:   if (nconv>0) {
113:     /*
114:        Display eigenvalues and relative errors
115:     */
116:     PetscPrintf(PETSC_COMM_WORLD,
117:          "           k          ||Ax-kx||/||kx||\n"
118:          "   ----------------- ------------------\n");

120:     for (i=0;i<nconv;i++) {
121:       /*
122:         Get converged eigenpairs: i-th eigenvalue is stored in kr (real part) and
123:         ki (imaginary part)
124:       */
125:       EPSGetEigenpair(eps,i,&kr,&ki,xr,xi);
126:       /*
127:          Compute the relative error associated to each eigenpair
128:       */
129:       EPSComputeError(eps,i,EPS_ERROR_RELATIVE,&error);

131: #if defined(PETSC_USE_COMPLEX)
132:       re = PetscRealPart(kr);
133:       im = PetscImaginaryPart(kr);
134: #else
135:       re = kr;
136:       im = ki;
137: #endif
138:       if (im!=0.0) {
139:         PetscPrintf(PETSC_COMM_WORLD," %9f%+9f j %12g\n",(double)re,(double)im,(double)error);
140:       } else {
141:         PetscPrintf(PETSC_COMM_WORLD,"   %12f       %12g\n",(double)re,(double)error);
142:       }
143:     }
144:     PetscPrintf(PETSC_COMM_WORLD,"\n");
145:   }

147:   /*
148:      Free work space
149:   */
150:   EPSDestroy(&eps);
151:   MatDestroy(&A);
152:   VecDestroy(&xr);
153:   VecDestroy(&xi);
154:   SlepcFinalize();
155:   return 0;
156: }