rnatively, for an in-place r2c transform, as described in the C
documentation we must <em>pad</em> the <em>first</em> dimension of the
real input with an extra two entries (which are ignored by FFTW) so as
to leave enough space for the complex output. The input is
<em>allocated</em> as a 2[L/2+1]&nbsp;&times;&nbsp;M&nbsp;&times;&nbsp;N
 array, even though only
L&nbsp;&times;&nbsp;M&nbsp;&times;&nbsp;N
 of it is actually used.  In this example, we will
allocate the array as a pointer type, using &lsquo;<samp