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<h3 class="section">4.2 Using Plans</h3>

<p>Plans for all transform types in FFTW are stored as type
<code>fftw_plan</code> (an opaque pointer type), and are created by one of the
various planning routines described in the following sections.
<a name="index-fftw_005fplan-146"></a>An <code>fftw_plan</code> contains all information necessary to compute the
transform, including the pointers to the input and output arrays.

<pre class="example">     void fftw_execute(const fftw_plan plan);
</pre>
   <p><a name="index-fftw_005fexecute-147"></a>
This executes the <code>plan</code>, to compute the corresponding transform on
the arrays for which it was planned (which must still exist).  The plan
is not modified, and <code>fftw_execute</code> can be called as many times as
desired.

   <p>To apply a given plan to a different array, you can use the new-array execute
interface.  See <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>.

   <p><code>fftw_execute</code> (and equivalents) is the only function in FFTW
guaranteed to be thread-safe; see <a href="Thread-safety.html#Thread-safety">Thread safety</a>.

   <p>This function:
<pre class="example">     void fftw_destroy_plan(fftw_plan plan);
</pre>
   <p><a name="index-fftw_005fdestroy_005fplan-148"></a>deallocates the <code>plan</code> and all its associated data.

   <p>FFTW's planner saves some other persistent data, such as the
accumulated wisdom and a list of algorithms available in the current
configuration.  If you want to deallocate all of that and reset FFTW
to the pristine state it was in when you started your program, you can
call:

<pre class="example">     void fftw_cleanup(void);
</pre>
   <p><a name="index-fftw_005fcleanup-149"></a>
After calling <code>fftw_cleanup</code>, all existing plans become undefined,
and you should not attempt to execute them nor to destroy them.  You can
however create and execute/destroy new plans, in which case FFTW starts
accumulating wisdom information again.

   <p><code>fftw_cleanup</code> does not deallocate your plans; you should still
call <code>fftw_destroy_plan</code> for this purpose.

   <p>The following two routines are provided purely for academic purposes
(that is, for entertainment).

<pre class="example">     void fftw_flops(const fftw_plan plan,
                     double *add, double *mul, double *fma);
</pre>
   <p><a name="index-fftw_005fflops-150"></a>
Given a <code>plan</code>, set <code>add</code>, <code>mul</code>, and <code>fma</code> to an
exact count of the number of floating-point additions, multiplications,
and fused multiply-add operations involved in the plan's execution.  The
total number of floating-point operations (flops) is <code>add + mul +
2*fma</code>, or <code>add + mul + fma</code> if the hardware supports fused
multiply-add instructions (although the number of FMA operations is only
approximate because of compiler voodoo).  (The number of operations
should be an integer, but we use <code>double</code> to avoid overflowing
<code>int</code> for large transforms; the arguments are of type <code>double</code>
even for single and long-double precision versions of FFTW.)

<pre class="example">     void fftw_fprint_plan(const fftw_plan plan, FILE *output_file);
     void fftw_print_plan(const fftw_plan plan);
</pre>
   <p><a name="index-fftw_005ffprint_005fplan-151"></a><a name="index-fftw_005fprint_005fplan-152"></a>
This outputs a &ldquo;nerd-readable&rdquo; representation of the <code>plan</code> to
the given file or to <code>stdout</code>, respectively.

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author	Geogaddi\David <d.m.ronan@qmul.ac.uk>
date	Fri, 10 Jul 2015 00:33:15 +0100
parents	25bf17994ef1
children