Date: 2026-05-01T10:02:08+00:00

Actual source code: test5.c

      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[] = "Test changing MFN type.\n\n";

     13: #include <slepcmfn.h>

     15: int main(int argc,char **argv)
     16: {
     17:   Mat            A;           /* problem matrix */
     18:   MFN            mfn;
     19:   FN             f;
     20:   PetscReal      norm;
     21:   PetscScalar    t=0.3;
     22:   PetscInt       N,n=25,m,Istart,Iend,II,i,j;
     23:   PetscBool      flag;
     24:   Vec            v,y;

     26:   PetscFunctionBeginUser;
     27:   PetscCall(SlepcInitialize(&argc,&argv,NULL,help));

     29:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL));
     30:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag));
     31:   if (!flag) m=n;
     32:   N = n*m;
     33:   PetscCall(PetscOptionsGetScalar(NULL,NULL,"-t",&t,NULL));
     34:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\nMatrix exponential y=exp(t*A)*e, of the 2-D Laplacian, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid)\n\n",N,n,m));

     36:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     37:                          Build the 2-D Laplacian
     38:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     40:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
     41:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N));
     42:   PetscCall(MatSetFromOptions(A));

     44:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
     45:   for (II=Istart;II<Iend;II++) {
     46:     i = II/n; j = II-i*n;
     47:     if (i>0) PetscCall(MatSetValue(A,II,II-n,-1.0,INSERT_VALUES));
     48:     if (i<m-1) PetscCall(MatSetValue(A,II,II+n,-1.0,INSERT_VALUES));
     49:     if (j>0) PetscCall(MatSetValue(A,II,II-1,-1.0,INSERT_VALUES));
     50:     if (j<n-1) PetscCall(MatSetValue(A,II,II+1,-1.0,INSERT_VALUES));
     51:     PetscCall(MatSetValue(A,II,II,4.0,INSERT_VALUES));
     52:   }

     54:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
     55:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

     57:   /* set v = ones(n,1) */
     58:   PetscCall(MatCreateVecs(A,&v,&y));
     59:   PetscCall(VecSet(v,1.0));

     61:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     62:                 Create the solver and set various options
     63:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     65:   PetscCall(FNCreate(PETSC_COMM_WORLD,&f));
     66:   PetscCall(FNSetType(f,FNEXP));

     68:   PetscCall(MFNCreate(PETSC_COMM_WORLD,&mfn));
     69:   PetscCall(MFNSetOperator(mfn,A));
     70:   PetscCall(MFNSetType(mfn,MFNEXPOKIT));
     71:   PetscCall(MFNSetDimensions(mfn,24));
     72:   PetscCall(MFNSetTolerances(mfn,1e-5,1000));
     73:   PetscCall(MFNSetFN(mfn,f));
     74:   PetscCall(MFNSetErrorIfNotConverged(mfn,PETSC_TRUE));
     75:   PetscCall(MFNSetFromOptions(mfn));
     76:   PetscCall(MFNView(mfn,NULL));

     78:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     79:             Change MFN type and solve the problem, y=exp(t*A)*v
     80:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     82:   PetscCall(MFNSetType(mfn,MFNKRYLOV));
     83:   PetscCall(FNSetScale(f,t,1.0));
     84:   PetscCall(MFNSolve(mfn,v,y));
     85:   PetscCall(VecNorm(y,NORM_2,&norm));
     86:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," Computed vector at time t=%.4g has norm %g\n\n",(double)PetscRealPart(t),(double)norm));

     88:   /*
     89:      Free work space
     90:   */
     91:   PetscCall(MFNDestroy(&mfn));
     92:   PetscCall(FNDestroy(&f));
     93:   PetscCall(MatDestroy(&A));
     94:   PetscCall(VecDestroy(&v));
     95:   PetscCall(VecDestroy(&y));
     96:   PetscCall(SlepcFinalize());
     97:   return 0;
     98: }

    100: /*TEST

    102:    test:

    104: TEST*/