4.5.5 Guru Real-to-real Transforms

fftw_plan fftw_plan_guru_r2r(int rank, const fftw_iodim *dims,
                             int howmany_rank,
                             const fftw_iodim *howmany_dims,
                             double *in, double *out,
                             const fftw_r2r_kind *kind,
                             unsigned flags);

Plan a real-to-real (r2r) multi-dimensional FFTW_FORWARD transform with transform dimensions given by (rank, dims) over a multi-dimensional vector (loop) of dimensions (howmany_rank, howmany_dims). dims and howmany_dims should point to fftw_iodim arrays of length rank and howmany_rank, respectively.

The transform kind of each dimension is given by the kind parameter, which should point to an array of length rank. Valid fftw_r2r_kind constants are given in Real-to-Real Transform Kinds.

in and out point to the real input and output arrays; they may be the same, indicating an in-place transform.

flags is a bitwise OR (‘|’) of zero or more planner flags, as defined in Planner Flags.