e latter is much slower.
FFTW does not deal with this problem, however&mdash;it assumes that your
processes run on hardware of comparable speed, and that the goal is
therefore to divide the problem as equally as possible.
</p>
<p>For a multi-dimensional complex DFT, FFTW can divide the problem
equally among the processes if: (i) the <em>first</em> dimension
<code>n0</code> is divisible by <em>P</em>; and (ii), the <em>product</em> of
the subsequent dimensions is divisible by <em>P</em>.  (For the advanced
i