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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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                  <a href="#libgwyprocess-simpleFFT.description" class="shortcut">Description</a></span>
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<a name="libgwyprocess-simpleFFT"></a><div class="titlepage"></div>
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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>
</td>
<td class="gallery_image" valign="top" align="right"></td>
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<div class="refsect1">
<a name="libgwyprocess-simpleFFT.functions"></a><h2>Functions</h2>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="functions_return">
<col class="functions_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 &lt;libprocess/gwyprocess.h&gt;
</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.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 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="refsect3">
<a name="id-1.25.6.2.8"></a><h4>Parameters</h4>
<div class="informaltable"><table 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="id-1.25.6.3.5"></a><h4>Parameters</h4>
<div class="informaltable"><table 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>
<div class="refsect3">
<a name="id-1.25.6.4.5"></a><h4>Parameters</h4>
<div class="informaltable"><table 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.other_details"></a><h2>Types and Values</h2>
</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><p>           -- high-level integral transform functions</p>
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