at, the output of
<code>FFTW_R2HC</code>/<code>FFTW_HC2R</code> is otherwise exactly the same as for
the corresponding 1d r2c/c2r transform
(i.e. <code>FFTW_FORWARD</code>/<code>FFTW_BACKWARD</code> transforms, respectively).
Recall that these transforms are unnormalized, so r2hc followed by hc2r
will result in the original data multiplied by <code>n</code>.  Furthermore,
like the c2r transform, an out-of-place hc2r transform will
<em>destroy its input</em> array.
</p>
<p>Although these halfcomplex transfor