ode> is a special planning mode in which the plan
is only created if wisdom is available for the given problem, and
otherwise a <code>NULL</code> plan is returned.  This can be combined with
other flags, e.g. &lsquo;<samp>FFTW_WISDOM_ONLY | FFTW_PATIENT</samp>&rsquo; creates a
plan only if wisdom is available that was created in
<code>FFTW_PATIENT</code> or <code>FFTW_EXHAUSTIVE</code> mode.  The
<code>FFTW_WISDOM_ONLY</code> flag is intended for users who need to detect
whether wisdom is available; for exa