nk</code> and
<code>howmany_rank</code>, respectively.  As for the basic and advanced
interfaces, an r2c transform is <code>FFTW_FORWARD</code> and a c2r transform
is <code>FFTW_BACKWARD</code>.
</p>
<p>The <em>last</em> dimension of <code>dims</code> is interpreted specially:
that dimension of the real array has size <code>dims[rank-1].n</code>, but
that dimension of the complex array has size <code>dims[rank-1].n/2+1</code>
(division rounded down).  The strides, on the other hand, are taken to
be exactly 