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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>simpleFFT: Gwyddion Data Processing Library Reference Manual</title>
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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="refsect1">
<a name="libgwyprocess-simpleFFT.functions"></a><h2>Functions</h2>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="functions_proto_type">
<col class="functions_proto_name">
</colgroup>
<tbody>
<tr>
<td class="function_type">
<span class="returnvalue">void</span>
</td>
<td class="function_name">
<a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-simple" title="gwy_fft_simple ()">gwy_fft_simple</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<span class="returnvalue">void</span>
</td>
<td class="function_name">
<a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-window" title="gwy_fft_window ()">gwy_fft_window</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<span class="returnvalue">void</span>
</td>
<td class="function_name">
<a class="link" href="libgwyprocess-simpleFFT.html#gwy-fft-window-data-field" title="gwy_fft_window_data_field ()">gwy_fft_window_data_field</a> <span class="c_punctuation">()</span>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect1">
<a name="libgwyprocess-simpleFFT.includes"></a><h2>Includes</h2>
<pre class="synopsis">#include <libprocess/gwyprocess.h>
</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> used to be employed as a fallback by other functions when
a better implementation (FFTW3) was not available. Since version 2.49 it just calls the corresponding FFTW
routine.</p>
<p>Generally, you should either use high-level Gwyddion functions such as <a class="link" href="libgwyprocess-inttrans.html#gwy-data-field-2dfft-raw" title="gwy_data_field_2dfft_raw ()"><code class="function">gwy_data_field_2dfft_raw()</code></a> or, if they are
insufficient, FFTW routines directly.</p>
<p>Up to version 2.7 simpleFFT required 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.functions_details"></a><h2>Functions</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 that used to be employed by other FFT functions when no better backend was available.
Since version 2.49 it just calls the corresponding FFTW routine.</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="refsect3">
<a name="gwy-fft-simple.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>dir</p></td>
<td class="parameter_description"><p>Transformation direction.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>n</p></td>
<td class="parameter_description"><p>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.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>istride</p></td>
<td class="parameter_description"><p>Input data stride.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>in_re</p></td>
<td class="parameter_description"><p>Real part of input data.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>in_im</p></td>
<td class="parameter_description"><p>Imaginary part of input data.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>ostride</p></td>
<td class="parameter_description"><p>Output data stride.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out_re</p></td>
<td class="parameter_description"><p>Real part of output data.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out_im</p></td>
<td class="parameter_description"><p>Imaginary part of output data.</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</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="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>);</pre>
<p>Multiplies data by given window.</p>
<div class="refsect3">
<a name="gwy-fft-window.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>n</p></td>
<td class="parameter_description"><p>Number of data values.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>data</p></td>
<td class="parameter_description"><p>Data values.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>windowing</p></td>
<td class="parameter_description"><p>Method used for windowing.</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</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>
<p>This is an old alias for <a class="link" href="libgwyprocess-inttrans.html#gwy-data-field-fft-window-1d" title="gwy_data_field_fft_window_1d ()"><code class="function">gwy_data_field_fft_window_1d()</code></a>.</p>
<div class="refsect3">
<a name="gwy-fft-window-data-field.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>dfield</p></td>
<td class="parameter_description"><p>A data field.</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>orientation</p></td>
<td class="parameter_description"><p>Windowing orientation (the same as corresponding FFT orientation).</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>windowing</p></td>
<td class="parameter_description"><p>The windowing type to use.</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</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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