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

  4: #include <petscmat.h>

  6: int main(int argc, char **args)
  7: {
  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:   PetscFunctionBeginUser;
 18:   PetscCall(PetscInitialize(&argc, &args, NULL, help));
 19:   PetscCheck(!PetscDefined(USE_COMPLEX), PETSC_COMM_WORLD, PETSC_ERR_SUP, "This example requires real numbers");

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

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

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

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

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

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

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

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

 55:   /* Check accuracy */
 56:   fac = 1.0 / (PetscReal)N;
 57:   PetscCall(VecScale(output, fac));
 58:   PetscCall(VecAXPY(output, -1.0, input));
 59:   PetscCall(VecNorm(output, NORM_1, &enorm));
 60:   if (enorm > 1.e-11 && rank == 0) PetscCall(PetscPrintf(PETSC_COMM_SELF, "  Error norm of |x - z| %e\n", enorm));

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

 71:   PetscCall(PetscFinalize());
 72:   return 0;
 73: }

 75: /*TEST

 77:    build:
 78:       requires: fftw !complex

 80:    test:
 81:       output_file: output/empty.out

 83:    test:
 84:       suffix: 2
 85:       nsize: 3
 86:       output_file: output/empty.out

 88: TEST*/