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<h4 class="subsection">4.4.2 Advanced Real-data DFTs</h4>
<pre class="example"> fftw_plan fftw_plan_many_dft_r2c(int rank, const int *n, int howmany,
double *in, const int *inembed,
int istride, int idist,
fftw_complex *out, const int *onembed,
int ostride, int odist,
unsigned flags);
fftw_plan fftw_plan_many_dft_c2r(int rank, const int *n, int howmany,
fftw_complex *in, const int *inembed,
int istride, int idist,
double *out, const int *onembed,
int ostride, int odist,
unsigned flags);
</pre>
<p><a name="index-fftw_005fplan_005fmany_005fdft_005fr2c-236"></a><a name="index-fftw_005fplan_005fmany_005fdft_005fc2r-237"></a>
Like <code>fftw_plan_many_dft</code>, these two functions add <code>howmany</code>,
<code>nembed</code>, <code>stride</code>, and <code>dist</code> parameters to the
<code>fftw_plan_dft_r2c</code> and <code>fftw_plan_dft_c2r</code> functions, but
otherwise behave the same as the basic interface.
<p>The interpretation of <code>howmany</code>, <code>stride</code>, and <code>dist</code> are
the same as for <code>fftw_plan_many_dft</code>, above. Note that the
<code>stride</code> and <code>dist</code> for the real array are in units of
<code>double</code>, and for the complex array are in units of
<code>fftw_complex</code>.
<p>If an <code>nembed</code> parameter is <code>NULL</code>, it is interpreted as what
it would be in the basic interface, as described in <a href="Real_002ddata-DFT-Array-Format.html#Real_002ddata-DFT-Array-Format">Real-data DFT Array Format</a>. That is, for the complex array the size is assumed to be
the same as <code>n</code>, but with the last dimension cut roughly in half.
For the real array, the size is assumed to be <code>n</code> if the transform
is out-of-place, or <code>n</code> with the last dimension “padded” if the
transform is in-place.
<p>If an <code>nembed</code> parameter is non-<code>NULL</code>, it is interpreted as
the physical size of the corresponding array, in row-major order, just
as for <code>fftw_plan_many_dft</code>. In this case, each dimension of
<code>nembed</code> should be <code>>=</code> what it would be in the basic
interface (e.g. the halved or padded <code>n</code>).
<p>Arrays <code>n</code>, <code>inembed</code>, and <code>onembed</code> are not used after
this function returns. You can safely free or reuse them.
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