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";

  4:  #include <petscmat.h>

  6: int main(int argc,char **args)
  7: {
  9:   PetscMPIInt    rank,size;
 10:   PetscInt       N0=50,N1=50,N=N0*N1;
 11:   PetscRandom    rdm;
 12:   PetscReal      enorm;
 13:   Vec            x,y,z,input,output;
 14:   Mat            A;
 15:   PetscInt       DIM,dim[2];
 16:   PetscReal      fac;

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

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

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

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

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

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

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

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

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

 56:   /* Check accuracy */
 57:   fac  = 1.0/(PetscReal)N;
 58:   VecScale(output,fac);
 59:   VecAXPY(output,-1.0,input);
 60:   VecNorm(output,NORM_1,&enorm);
 61:   if (enorm > 1.e-11 && !rank) {
 62:     PetscPrintf(PETSC_COMM_SELF,"  Error norm of |x - z| %e\n",enorm);
 63:   }

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

 74:   PetscFinalize();
 75:   return ierr;
 76: }





 82: /*TEST

 84:    build:
 85:       requires: fftw !complex

 87:    test:
 88:       output_file: output/ex148.out

 90:    test:
 91:       suffix: 2
 92:       nsize: 3
 93:       output_file: output/ex148.out

 95: TEST*/