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fftw_plan fftw_plan_dft_r2c_1d(int n0, Chris@19: double *in, fftw_complex *out, Chris@19: unsigned flags); Chris@19: fftw_plan fftw_plan_dft_r2c_2d(int n0, int n1, Chris@19: double *in, fftw_complex *out, Chris@19: unsigned flags); Chris@19: fftw_plan fftw_plan_dft_r2c_3d(int n0, int n1, int n2, Chris@19: double *in, fftw_complex *out, Chris@19: unsigned flags); Chris@19: fftw_plan fftw_plan_dft_r2c(int rank, const int *n, Chris@19: double *in, fftw_complex *out, Chris@19: unsigned flags); Chris@19:Chris@19:
Chris@19: Plan a real-input/complex-output discrete Fourier transform (DFT) in
Chris@19: zero or more dimensions, returning an fftw_plan (see Using Plans).
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Once you have created a plan for a certain transform type and Chris@19: parameters, then creating another plan of the same type and parameters, Chris@19: but for different arrays, is fast and shares constant data with the Chris@19: first plan (if it still exists). Chris@19: Chris@19:
The planner returns NULL if the plan cannot be created. A
Chris@19: non-NULL plan is always returned by the basic interface unless
Chris@19: you are using a customized FFTW configuration supporting a restricted
Chris@19: set of transforms, or if you use the FFTW_PRESERVE_INPUT flag
Chris@19: with a multi-dimensional out-of-place c2r transform (see below).
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rank is the rank of the transform (it should be the size of the
Chris@19: array *n), and can be any non-negative integer. (See Complex Multi-Dimensional DFTs, for the definition of “rank”.) The
Chris@19: ‘_1d’, ‘_2d’, and ‘_3d’ planners correspond to a
Chris@19: rank of 1, 2, and 3, respectively. The rank
Chris@19: may be zero, which is equivalent to a rank-1 transform of size 1, i.e. a
Chris@19: copy of one real number (with zero imaginary part) from input to output.
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Chris@19: n0, n1, n2, or n[0..rank-1], (as appropriate
Chris@19: for each routine) specify the size of the transform dimensions. They
Chris@19: can be any positive integer. This is different in general from the
Chris@19: physical array dimensions, which are described in Real-data DFT Array Format.
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Chris@19: in and out point to the input and output arrays of the
Chris@19: transform, which may be the same (yielding an in-place transform).
Chris@19: These arrays are overwritten during planning, unless
Chris@19: FFTW_ESTIMATE is used in the flags. (The arrays need not be
Chris@19: initialized, but they must be allocated.) For an in-place transform, it
Chris@19: is important to remember that the real array will require padding,
Chris@19: described in Real-data DFT Array Format.
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Chris@19: flags is a bitwise OR (‘|’) of zero or more planner flags,
Chris@19: as defined in Planner Flags.
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Chris@19: The inverse transforms, taking complex input (storing the non-redundant Chris@19: half of a logically Hermitian array) to real output, are given by: Chris@19: Chris@19:
fftw_plan fftw_plan_dft_c2r_1d(int n0, Chris@19: fftw_complex *in, double *out, Chris@19: unsigned flags); Chris@19: fftw_plan fftw_plan_dft_c2r_2d(int n0, int n1, Chris@19: fftw_complex *in, double *out, Chris@19: unsigned flags); Chris@19: fftw_plan fftw_plan_dft_c2r_3d(int n0, int n1, int n2, Chris@19: fftw_complex *in, double *out, Chris@19: unsigned flags); Chris@19: fftw_plan fftw_plan_dft_c2r(int rank, const int *n, Chris@19: fftw_complex *in, double *out, Chris@19: unsigned flags); Chris@19:Chris@19:
Chris@19: The arguments are the same as for the r2c transforms, except that the Chris@19: input and output data formats are reversed. Chris@19: Chris@19:
FFTW computes an unnormalized transform: computing an r2c followed by a
Chris@19: c2r transform (or vice versa) will result in the original data
Chris@19: multiplied by the size of the transform (the product of the logical
Chris@19: dimensions).
Chris@19: An r2c transform produces the same output as a FFTW_FORWARD
Chris@19: complex DFT of the same input, and a c2r transform is correspondingly
Chris@19: equivalent to FFTW_BACKWARD. For more information, see What FFTW Really Computes.
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