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fftw3: Guru Real-data DFTs

 
 4.5.4 Guru Real-data DFTs
 -------------------------
 
      fftw_plan fftw_plan_guru_dft_r2c(
           int rank, const fftw_iodim *dims,
           int howmany_rank, const fftw_iodim *howmany_dims,
           double *in, fftw_complex *out,
           unsigned flags);
 
      fftw_plan fftw_plan_guru_split_dft_r2c(
           int rank, const fftw_iodim *dims,
           int howmany_rank, const fftw_iodim *howmany_dims,
           double *in, double *ro, double *io,
           unsigned flags);
 
      fftw_plan fftw_plan_guru_dft_c2r(
           int rank, const fftw_iodim *dims,
           int howmany_rank, const fftw_iodim *howmany_dims,
           fftw_complex *in, double *out,
           unsigned flags);
 
      fftw_plan fftw_plan_guru_split_dft_c2r(
           int rank, const fftw_iodim *dims,
           int howmany_rank, const fftw_iodim *howmany_dims,
           double *ri, double *ii, double *out,
           unsigned flags);
 
    Plan a real-input (r2c) or real-output (c2r), multi-dimensional DFT
 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.  As for the
 basic and advanced interfaces, an r2c transform is 'FFTW_FORWARD' and a
 c2r transform is 'FFTW_BACKWARD'.
 
    The _last_ dimension of 'dims' is interpreted specially: that
 dimension of the real array has size 'dims[rank-1].n', but that
 dimension of the complex array has size 'dims[rank-1].n/2+1' (division
 rounded down).  The strides, on the other hand, are taken to be exactly
 as specified.  It is up to the user to specify the strides appropriately
 for the peculiar dimensions of the data, and we do not guarantee that
 the planner will succeed (return non-'NULL') for any dimensions other
 than those described in Real-data DFT Array Format and
 generalized in Advanced Real-data DFTs.  (That is, for an
 in-place transform, each individual dimension should be able to operate
 in place.)
 
    'in' and 'out' point to the input and output arrays for r2c and c2r
 transforms, respectively.  For split arrays, 'ri' and 'ii' point to the
 real and imaginary input arrays for a c2r transform, and 'ro' and 'io'
 point to the real and imaginary output arrays for an r2c transform.
 'in' and 'ro' or 'ri' and 'out' may be the same, indicating an in-place
 transform.  (In-place transforms where 'in' and 'io' or 'ii' and 'out'
 are the same are not currently supported.)
 
    'flags' is a bitwise OR ('|') of zero or more planner flags, as
 defined in Planner Flags.
 
    In-place transforms of rank greater than 1 are currently only
 supported for interleaved arrays.  For split arrays, the planner will
 return 'NULL'.
 

Info Catalog fftw3: Guru Complex DFTs fftw3: Guru Interface fftw3: Guru Real-to-real Transforms