1: static char help[]="This program illustrates the use of PETSc-fftw interface for real 2D DFT.\n\
  2:                     See ~petsc/src/mat/examples/tests/ex158.c for general cases. \n\n";
  3:  #include <petscmat.h>

  5: int main(int argc,char **args)
  6: {
  8:   PetscMPIInt    rank,size;
  9:   PetscInt       N0=50,N1=50,N=N0*N1;
 10:   PetscRandom    rdm;
 11:   PetscReal      enorm;
 12:   Vec            x,y,z,input,output;
 13:   Mat            A;
 14:   PetscInt       DIM,dim[2];
 15:   PetscReal      fac;

 17:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 18: #if defined(PETSC_USE_COMPLEX)
 19:   SETERRQ(PETSC_COMM_WORLD,PETSC_ERR_SUP, "This example requires real numbers");
 20: #endif

 22:   MPI_Comm_size(PETSC_COMM_WORLD, &size);
 23:   MPI_Comm_rank(PETSC_COMM_WORLD, &rank);

 25:   /* Create and set PETSc vectors 'input' and 'output' */
 26:   PetscRandomCreate(PETSC_COMM_WORLD, &rdm);
 27:   PetscRandomSetFromOptions(rdm);

 29:   VecCreate(PETSC_COMM_WORLD,&input);
 30:   VecSetSizes(input,PETSC_DECIDE,N0*N1);
 31:   VecSetFromOptions(input);
 32:   VecSetRandom(input,rdm);
 33:   VecDuplicate(input,&output);
 34:   PetscObjectSetName((PetscObject)input, "Real space vector");
 35:   PetscObjectSetName((PetscObject)output, "Reconstructed vector");

 37:   /* Get FFTW vectors 'x', 'y' and 'z' */
 38:   DIM    = 2;
 39:   dim[0] = N0; dim[1] = N1;
 40:   MatCreateFFT(PETSC_COMM_WORLD,DIM,dim,MATFFTW,&A);
 41:   MatCreateVecsFFTW(A,&x,&y,&z);

 43:   /* Scatter PETSc vector 'input' to FFTW vector 'x' */
 44:   VecScatterPetscToFFTW(A,input,x);

 46:   /* Apply forward FFT */
 47:   MatMult(A,x,y);

 49:   /* Apply backward FFT */
 50:   MatMultTranspose(A,y,z);

 52:   /* Scatter FFTW vector 'z' to PETSc vector 'output' */
 53:   VecScatterFFTWToPetsc(A,z,output);

 55:   /* Check accuracy */
 56:   fac  = 1.0/(PetscReal)N;
 57:   VecScale(output,fac);
 58:   VecAXPY(output,-1.0,input);
 59:   VecNorm(output,NORM_1,&enorm);
 60:   if (enorm > 1.e-11 && !rank) {
 61:     PetscPrintf(PETSC_COMM_SELF,"  Error norm of |x - z| %e\n",enorm);
 62:   }

 64:   /* Free spaces */
 65:   PetscRandomDestroy(&rdm);
 66:   VecDestroy(&input);
 67:   VecDestroy(&output);
 68:   VecDestroy(&x);
 69:   VecDestroy(&y);
 70:   VecDestroy(&z);
 71:   MatDestroy(&A);

 73:   PetscFinalize();
 74:   return ierr;
 75: }