li><li> <em>If</em> you pass <em>different</em> input/output arrays compared to
those used when creating the plan, you must abide by all the
restrictions of the new-array execute functions (see <a href="New_002darray-Execute-Functions.html">New-array Execute Functions</a>).  The most tricky of these is the
requirement that the new arrays have the same alignment as the
original arrays; the best (and possibly only) way to guarantee this
is to use the &lsquo;<samp>fftw_alloc</samp>&rsquo; functions to allocate