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<h4 class="subsection">4.5.3 Guru Complex DFTs</h4>

<pre class="example"> fftw_plan fftw_plan_guru_dft(

int rank, const fftw_iodim *dims,

int howmany_rank, const fftw_iodim *howmany_dims,

fftw_complex *in, fftw_complex *out,

int sign, unsigned flags);

fftw_plan fftw_plan_guru_split_dft(

int rank, const fftw_iodim *dims,

int howmany_rank, const fftw_iodim *howmany_dims,

double *ri, double *ii, double *ro, double *io,

unsigned flags);

</pre>

These two functions plan a complex-data, multi-dimensional DFT

for the interleaved and split format, respectively.

Transform dimensions are given by (<code>rank</code>, <code>dims</code>) over a

multi-dimensional vector (loop) of dimensions (<code>howmany_rank</code>,

<code>howmany_dims</code>). <code>dims</code> and <code>howmany_dims</code> should point

to <code>fftw_iodim</code> arrays of length <code>rank</code> and

<code>howmany_rank</code>, respectively.

<p><a name="index-flags-240"></a><code>flags</code> is a bitwise OR (`<samp><span class="samp">|</span></samp>') of zero or more planner flags,

as defined in <a href="Planner-Flags.html#Planner-Flags">Planner Flags</a>.

<p>In the <code>fftw_plan_guru_dft</code> function, the pointers <code>in</code> and

<code>out</code> point to the interleaved input and output arrays,

respectively. The sign can be either -1 (=

<code>FFTW_FORWARD</code>) or +1 (= <code>FFTW_BACKWARD</code>). If the

pointers are equal, the transform is in-place.

<p>In the <code>fftw_plan_guru_split_dft</code> function,

<code>ri</code> and <code>ii</code> point to the real and imaginary input arrays,

and <code>ro</code> and <code>io</code> point to the real and imaginary output

arrays. The input and output pointers may be the same, indicating an

in-place transform. For example, for <code>fftw_complex</code> pointers

<code>in</code> and <code>out</code>, the corresponding parameters are:

<pre class="example"> ri = (double *) in;

ii = (double *) in + 1;

ro = (double *) out;

io = (double *) out + 1;

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</pre>

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<p>Because <code>fftw_plan_guru_split_dft</code> accepts split arrays, strides

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are expressed in units of <code>double</code>. For a contiguous

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<code>fftw_complex</code> array, the overall stride of the transform should

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be 2, the distance between consecutive real parts or between

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consecutive imaginary parts; see <a href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes">Guru vector and transform sizes</a>. Note that the dimension strides are applied equally to the

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real and imaginary parts; real and imaginary arrays with different

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strides are not supported.

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<p>There is no <code>sign</code> parameter in <code>fftw_plan_guru_split_dft</code>.

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This function always plans for an <code>FFTW_FORWARD</code> transform. To

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plan for an <code>FFTW_BACKWARD</code> transform, you can exploit the

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identity that the backwards DFT is equal to the forwards DFT with the

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real and imaginary parts swapped. For example, in the case of the

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<code>fftw_complex</code> arrays above, the <code>FFTW_BACKWARD</code> transform

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is computed by the parameters:

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<pre class="example"> ri = (double *) in + 1;

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ii = (double *) in;

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ro = (double *) out + 1;

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io = (double *) out;

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</pre>

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