static char help[] = "Test sequential FFTW interface \n\n";

/*
  Compiling the code:
      This code uses the complex numbers version of PETSc, so configure
      must be run to enable this

*/

#include <petscmat.h>
int main(int argc, char **args)
{
  typedef enum {
    RANDOM,
    CONSTANT,
    TANH,
    NUM_FUNCS
  } FuncType;
  const char *funcNames[NUM_FUNCS] = {"random", "constant", "tanh"};
  Mat         A;
  PetscMPIInt size;
  PetscInt    n = 10, N, ndim = 4, dim[4], DIM, i;
  Vec         x, y, z;
  PetscScalar s;
  PetscRandom rdm;
  PetscReal   enorm, tol = PETSC_SMALL;
  PetscInt    func;
  FuncType    function = RANDOM;
  PetscBool   view     = PETSC_FALSE;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCheck(size == 1, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "This is a uniprocessor example only!");
  PetscOptionsBegin(PETSC_COMM_WORLD, NULL, "FFTW Options", "ex112");
  PetscCall(PetscOptionsEList("-function", "Function type", "ex112", funcNames, NUM_FUNCS, funcNames[function], &func, NULL));
  PetscCall(PetscOptionsBool("-vec_view_draw", "View the functions", "ex112", view, &view, NULL));
  function = (FuncType)func;
  PetscOptionsEnd();

  for (DIM = 0; DIM < ndim; DIM++) dim[DIM] = n; /* size of transformation in DIM-dimension */
  PetscCall(PetscRandomCreate(PETSC_COMM_SELF, &rdm));
  PetscCall(PetscRandomSetFromOptions(rdm));

  for (DIM = 1; DIM < 5; DIM++) {
    for (i = 0, N = 1; i < DIM; i++) N *= dim[i];
    PetscCall(PetscPrintf(PETSC_COMM_SELF, "\n %d-D: FFTW on vector of size %d \n", DIM, N));

    /* create FFTW object */
    PetscCall(MatCreateFFT(PETSC_COMM_SELF, DIM, dim, MATFFTW, &A));

    /* create vectors of length N=n^DIM */
    PetscCall(MatCreateVecs(A, &x, &y));
    PetscCall(MatCreateVecs(A, &z, NULL));
    PetscCall(PetscObjectSetName((PetscObject)x, "Real space vector"));
    PetscCall(PetscObjectSetName((PetscObject)y, "Frequency space vector"));
    PetscCall(PetscObjectSetName((PetscObject)z, "Reconstructed vector"));

    /* set values of space vector x */
    if (function == RANDOM) {
      PetscCall(VecSetRandom(x, rdm));
    } else if (function == CONSTANT) {
      PetscCall(VecSet(x, 1.0));
    } else if (function == TANH) {
      PetscScalar *a;
      PetscCall(VecGetArray(x, &a));
      for (i = 0; i < N; ++i) a[i] = tanh((i - N / 2.0) * (10.0 / N));
      PetscCall(VecRestoreArray(x, &a));
    }
    if (view) PetscCall(VecView(x, PETSC_VIEWER_DRAW_WORLD));

    /* apply FFTW_FORWARD and FFTW_BACKWARD several times on same x, y, and z */
    for (i = 0; i < 3; i++) {
      PetscCall(MatMult(A, x, y));
      if (view && i == 0) PetscCall(VecView(y, PETSC_VIEWER_DRAW_WORLD));
      PetscCall(MatMultTranspose(A, y, z));

      /* compare x and z. FFTW computes an unnormalized DFT, thus z = N*x */
      s = 1.0 / (PetscReal)N;
      PetscCall(VecScale(z, s));
      if (view && i == 0) PetscCall(VecView(z, PETSC_VIEWER_DRAW_WORLD));
      PetscCall(VecAXPY(z, -1.0, x));
      PetscCall(VecNorm(z, NORM_1, &enorm));
      if (enorm > tol) PetscCall(PetscPrintf(PETSC_COMM_SELF, "  Error norm of |x - z| %g\n", (double)enorm));
    }

    /* apply FFTW_FORWARD and FFTW_BACKWARD several times on different x */
    for (i = 0; i < 3; i++) {
      PetscCall(VecDestroy(&x));
      PetscCall(VecCreateSeq(PETSC_COMM_SELF, N, &x));
      PetscCall(VecSetRandom(x, rdm));

      PetscCall(MatMult(A, x, y));
      PetscCall(MatMultTranspose(A, y, z));

      /* compare x and z. FFTW computes an unnormalized DFT, thus z = N*x */
      s = 1.0 / (PetscReal)N;
      PetscCall(VecScale(z, s));
      if (view && i == 0) PetscCall(VecView(z, PETSC_VIEWER_DRAW_WORLD));
      PetscCall(VecAXPY(z, -1.0, x));
      PetscCall(VecNorm(z, NORM_1, &enorm));
      if (enorm > tol) PetscCall(PetscPrintf(PETSC_COMM_SELF, "  Error norm of new |x - z| %g\n", (double)enorm));
    }

    /* free spaces */
    PetscCall(VecDestroy(&x));
    PetscCall(VecDestroy(&y));
    PetscCall(VecDestroy(&z));
    PetscCall(MatDestroy(&A));
  }
  PetscCall(PetscRandomDestroy(&rdm));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   build:
      requires: fftw complex

   test:
      args: -mat_fftw_plannerflags FFTW_ESTIMATE
      output_file: output/ex112.out

   test:
      suffix: 2
      args: -mat_fftw_plannerflags FFTW_MEASURE
      output_file: output/ex112.out
      requires: !defined(PETSC_USE_CXXCOMPLEX)

   test:
      suffix: 3
      args: -mat_fftw_plannerflags FFTW_PATIENT
      output_file: output/ex112.out

   test:
      suffix: 4
      args: -mat_fftw_plannerflags FFTW_EXHAUSTIVE
      output_file: output/ex112.out

TEST*/