fftw_plan fftw_plan_many_r2r(int rank, const int *n, int howmany,
double *in, const int *inembed,
int istride, int idist,
double *out, const int *onembed,
int ostride, int odist,
const fftw_r2r_kind *kind, unsigned flags);
Like fftw_plan_many_dft, this functions adds howmany,
nembed, stride, and dist parameters to the
fftw_plan_r2r function, but otherwise behave the same as the
basic interface. The interpretation of those additional parameters are
the same as for fftw_plan_many_dft. (Of course, the
stride and dist parameters are now in units of
double, not fftw_complex.)
Arrays n, inembed, onembed, and kind are not
used after this function returns. You can safely free or reuse them.