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<h2><span class="refentrytitle"><a name="libgwyprocess-simpleFFT.top_of_page"></a>simpleFFT</span></h2>
<p>simpleFFT — Simple FFT algorithm</p>
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<div class="refsynopsisdiv">
<a name="libgwyprocess-simpleFFT.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis">
#include <libprocess/gwyprocess.h>
<span class="returnvalue">void</span> <a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-simple" title="gwy_fft_simple ()">gwy_fft_simple</a> (<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyTransformDirection" title="enum GwyTransformDirection"><span class="type">GwyTransformDirection</span></a> dir</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> n</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> istride</code></em>,
<em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *in_re</code></em>,
<em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *in_im</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> ostride</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *out_re</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *out_im</code></em>);
<span class="returnvalue">void</span> <a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-window" title="gwy_fft_window ()">gwy_fft_window</a> (<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> n</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *data</code></em>,
<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyWindowingType" title="enum GwyWindowingType"><span class="type">GwyWindowingType</span></a> windowing</code></em>);
<span class="returnvalue">void</span> <a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-window-data-field" title="gwy_fft_window_data_field ()">gwy_fft_window_data_field</a> (<em class="parameter"><code><a class="link" href="GwyDataField.html" title="GwyDataField"><span class="type">GwyDataField</span></a> *dfield</code></em>,
<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyOrientation" title="enum GwyOrientation"><span class="type">GwyOrientation</span></a> orientation</code></em>,
<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyWindowingType" title="enum GwyWindowingType"><span class="type">GwyWindowingType</span></a> windowing</code></em>);
</pre>
</div>
<div class="refsect1">
<a name="libgwyprocess-simpleFFT.description"></a><h2>Description</h2>
<p>
The simple one-dimensional FFT algorithm <a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-simple" title="gwy_fft_simple ()"><code class="function">gwy_fft_simple()</code></a> is used as
a fallback by other functions when a better implementation (FFTW3) is not
available.
</p>
<p>
You should not use it directly, as it is a waste of resources
if FFTW3 backed is in use, neither you should feel any need to, as
high-level functions such as <a class="link" href="libgwyprocess-inttrans.html#gwy-data-field-2dfft" title="gwy_data_field_2dfft ()"><code class="function">gwy_data_field_2dfft()</code></a> are available.
</p>
<p>
Up to version 2.7 simpleFFT works only with certain tranform sizes, mostly
powers of 2. Since 2.8 it can handle arbitrary tranform sizes, although
sizes with large prime factors can be quite slow (still O(n*log(n)) though).
</p>
</div>
<div class="refsect1">
<a name="libgwyprocess-simpleFFT.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="gwy-fft-simple"></a><h3>gwy_fft_simple ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> gwy_fft_simple (<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyTransformDirection" title="enum GwyTransformDirection"><span class="type">GwyTransformDirection</span></a> dir</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> n</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> istride</code></em>,
<em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *in_re</code></em>,
<em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *in_im</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> ostride</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *out_re</code></em>,
<em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *out_im</code></em>);</pre>
<p>
Performs a DFT algorithm.
</p>
<p>
This is a low-level function used by other FFT functions when no better
backend is available.
</p>
<p>
Strides are distances between samples in input and output arrays. Use 1
for normal `dense' arrays. To use <a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-simple" title="gwy_fft_simple ()"><code class="function">gwy_fft_simple()</code></a> with interleaved arrays,
that is with alternating real and imaginary data, call it with
<em class="parameter"><code>istride</code></em>=2, <em class="parameter"><code>in_re</code></em>=<em class="parameter"><code>complex_array</code></em>, <em class="parameter"><code>in_im</code></em>=<em class="parameter"><code>complex_array</code></em>+1 (and similarly
for output arrays).
</p>
<p>
The output is symmetrically normalized by square root of <em class="parameter"><code>n</code></em> for both
transform directions. By performing forward and then backward transform,
you will obtain the original array (up to rounding errors).
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>dir</code></em> :</span></p></td>
<td>Transformation direction.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>n</code></em> :</span></p></td>
<td>Number of data points. Note only certain transform sizes are
implemented. If <a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-simple" title="gwy_fft_simple ()"><code class="function">gwy_fft_simple()</code></a> is the current FFT backend, then
<a class="link" href="libgwyprocess-inttrans.html#gwy-fft-find-nice-size" title="gwy_fft_find_nice_size ()"><code class="function">gwy_fft_find_nice_size()</code></a> can provide accepted transform sizes.
If <a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-simple" title="gwy_fft_simple ()"><code class="function">gwy_fft_simple()</code></a> is not the current FFT backend, you should not
use it.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>istride</code></em> :</span></p></td>
<td>Input data stride.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>in_re</code></em> :</span></p></td>
<td>Real part of input data.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>in_im</code></em> :</span></p></td>
<td>Imaginary part of input data.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>ostride</code></em> :</span></p></td>
<td>Output data stride.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>out_re</code></em> :</span></p></td>
<td>Real part of output data.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>out_im</code></em> :</span></p></td>
<td>Imaginary part of output data.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-fft-window"></a><h3>gwy_fft_window ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> gwy_fft_window (<em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> n</code></em>,
<em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *data</code></em>,
<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyWindowingType" title="enum GwyWindowingType"><span class="type">GwyWindowingType</span></a> windowing</code></em>);</pre>
<p>
Multiplies data by given window.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>n</code></em> :</span></p></td>
<td>Number of data values.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>data</code></em> :</span></p></td>
<td>Data values.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>windowing</code></em> :</span></p></td>
<td>Method used for windowing.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-fft-window-data-field"></a><h3>gwy_fft_window_data_field ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> gwy_fft_window_data_field (<em class="parameter"><code><a class="link" href="GwyDataField.html" title="GwyDataField"><span class="type">GwyDataField</span></a> *dfield</code></em>,
<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyOrientation" title="enum GwyOrientation"><span class="type">GwyOrientation</span></a> orientation</code></em>,
<em class="parameter"><code><a class="link" href="libgwyprocess-gwyprocessenums.html#GwyWindowingType" title="enum GwyWindowingType"><span class="type">GwyWindowingType</span></a> windowing</code></em>);</pre>
<p>
Performs windowing of a data field in given direction.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>dfield</code></em> :</span></p></td>
<td>A data field.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>orientation</code></em> :</span></p></td>
<td>Windowing orientation (the same as corresponding FFT
orientation).</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>windowing</code></em> :</span></p></td>
<td>The windowing type to use.</td>
</tr>
</tbody>
</table></div>
</div>
</div>
<div class="refsect1">
<a name="libgwyprocess-simpleFFT.see-also"></a><h2>See Also</h2>
<a class="link" href="libgwyprocess-inttrans.html" title="inttrans">inttrans</a>
-- high-level integral transform functions
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