FFTW 3.3.8: Advanced Real-data DFTs

Chris@82:

fftw_plan fftw_plan_many_dft_r2c(int rank, const int *n, int howmany,
Chris@82:                                  double *in, const int *inembed,
Chris@82:                                  int istride, int idist,
Chris@82:                                  fftw_complex *out, const int *onembed,
Chris@82:                                  int ostride, int odist,
Chris@82:                                  unsigned flags);
Chris@82: fftw_plan fftw_plan_many_dft_c2r(int rank, const int *n, int howmany,
Chris@82:                                  fftw_complex *in, const int *inembed,
Chris@82:                                  int istride, int idist,
Chris@82:                                  double *out, const int *onembed,
Chris@82:                                  int ostride, int odist,
Chris@82:                                  unsigned flags);
Chris@82:

Like fftw_plan_many_dft, these two functions add howmany, Chris@82: nembed, stride, and dist parameters to the Chris@82: fftw_plan_dft_r2c and fftw_plan_dft_c2r functions, but Chris@82: otherwise behave the same as the basic interface. Chris@82:

The interpretation of howmany, stride, and dist are Chris@82: the same as for fftw_plan_many_dft, above. Note that the Chris@82: stride and dist for the real array are in units of Chris@82: double, and for the complex array are in units of Chris@82: fftw_complex. Chris@82:

If an nembed parameter is NULL, it is interpreted as what Chris@82: it would be in the basic interface, as described in Real-data DFT Array Format. That is, for the complex array the size is assumed to be Chris@82: the same as n, but with the last dimension cut roughly in half. Chris@82: For the real array, the size is assumed to be n if the transform Chris@82: is out-of-place, or n with the last dimension “padded” if the Chris@82: transform is in-place. Chris@82:

If an nembed parameter is non-NULL, it is interpreted as Chris@82: the physical size of the corresponding array, in row-major order, just Chris@82: as for fftw_plan_many_dft. In this case, each dimension of Chris@82: nembed should be >= what it would be in the basic Chris@82: interface (e.g. the halved or padded n). Chris@82:

Arrays n, inembed, and onembed are not used after Chris@82: this function returns. You can safely free or reuse them. Chris@82:

4.4.2 Advanced Real-data DFTs