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,(char*)0,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*/