KokkosFFT::irfftn

template<typename ExecutionSpace, typename InViewType, typename OutViewType, std::size_t DIM>
void KokkosFFT::irfftn(const ExecutionSpace &exec_space, const InViewType &in, const OutViewType &out, axis_type<DIM> axes = KokkosFFT::Impl::index_sequence<int, DIM, -static_cast<int>(DIM)>(), KokkosFFT::Normalization norm = KokkosFFT::Normalization::backward, shape_type<DIM> s = {})

Inverse of rfftn.

Template Parameters:

  • ExecutionSpace – The type of Kokkos execution space

  • InViewType – Input View type for the fft

  • OutViewType – Output View type for the fft

  • DIM – The dimensionality of the fft

Parameters:

  • exec_space – [in] Kokkos execution space

  • in – [in] Input data (complex)

  • out – [out] Output data (real)

  • axes – [in] Axes over which FFT is performed (default, all axes)

  • norm – [in] How the normalization is applied (default, backward)

  • s – [in] Shape of the transformed axis of the output (default, {})

Note

The input must be a complex-valued view, and the output must be a real-valued view. The input length along the transform axis (axes[DIM-1]) is n/2 + 1, where n is the output length along that axis. If this condition is not met, the std::runtime_error exception will be thrown.

Examples

In this example, we use the 3D View with LayoutRight to avoid the internal transpose. This allows irfftn to perform 3-dimensional inverse FFT on the outermost dimension without transpose.

 1#include <iostream>
 2#include <Kokkos_Core.hpp>
 3#include <Kokkos_Complex.hpp>
 4#include <KokkosFFT.hpp>
 5
 6/// \brief Example of irfftn usage in documentation
 7/// x_hat = [[[78, -6],
 8///           [-12, 0]],
 9///          [[-24+13.8564j, 0],
10///           [0, 0]],
11///          [[-24-13.8564j, 0],
12///           [0, 0]]]
13/// x = [[[1, 2],
14///       [3, 4]],
15///      [[5, 6],
16///       [7, 8]],
17///      [[9, 10],
18///       [11, 12]]]
19int main(int argc, char* argv[]) {
20  Kokkos::ScopeGuard guard(argc, argv);
21  using ExecutionSpace = Kokkos::DefaultExecutionSpace;
22  using View3D = Kokkos::View<double***, Kokkos::LayoutRight, ExecutionSpace>;
23  using ComplexView3D = Kokkos::View<Kokkos::complex<double>***,
24                                     Kokkos::LayoutRight, ExecutionSpace>;
25
26  const int n0 = 3, n1 = 2, n2 = 2;
27
28  ComplexView3D x_hat("x_hat", n0, n1, n2 / 2 + 1);
29  View3D x("x", n0, n1, n2);
30  auto h_x_hat     = Kokkos::create_mirror_view(x_hat);
31  h_x_hat(0, 0, 0) = Kokkos::complex<double>(78, 0);
32  h_x_hat(0, 0, 1) = Kokkos::complex<double>(-6, 0);
33  h_x_hat(0, 1, 0) = Kokkos::complex<double>(-12, 0);
34  h_x_hat(1, 0, 0) = Kokkos::complex<double>(-24, 13.8564);
35  h_x_hat(2, 0, 0) = Kokkos::complex<double>(-24, -13.8564);
36  Kokkos::deep_copy(x_hat, h_x_hat);
37
38  ExecutionSpace exec;
39  KokkosFFT::irfftn(exec, x_hat, x);
40
41  auto h_x = Kokkos::create_mirror_view_and_copy(Kokkos::HostSpace{}, x);
42  for (int i = 0; i < n0; ++i) {
43    for (int j = 0; j < n1; ++j) {
44      for (int k = 0; k < n2; ++k) {
45        std::cout << " " << h_x(i, j, k);
46      }
47      std::cout << std::endl;
48    }
49    std::cout << std::endl;
50  }
51
52  return 0;
53}

Expected output:

1 2
3 4

5 6
7 8

9 10
11 12