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<title>GNU Scientific Library – Reference Manual: DWT Examples</title>
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<p>
Next: <a href="DWT-References.html#DWT-References" accesskey="n" rel="next">DWT References</a>, Previous: <a href="DWT-Transform-Functions.html#DWT-Transform-Functions" accesskey="p" rel="previous">DWT Transform Functions</a>, Up: <a href="Wavelet-Transforms.html#Wavelet-Transforms" accesskey="u" rel="up">Wavelet Transforms</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Examples-23"></a>
<h3 class="section">32.4 Examples</h3>
<p>The following program demonstrates the use of the one-dimensional
wavelet transform functions. It computes an approximation to an input
signal (of length 256) using the 20 largest components of the wavelet
transform, while setting the others to zero.
</p>
<div class="example">
<pre class="verbatim">#include <stdio.h>
#include <math.h>
#include <gsl/gsl_sort.h>
#include <gsl/gsl_wavelet.h>
int
main (int argc, char **argv)
{
(void)(argc); /* avoid unused parameter warning */
int i, n = 256, nc = 20;
double *data = malloc (n * sizeof (double));
double *abscoeff = malloc (n * sizeof (double));
size_t *p = malloc (n * sizeof (size_t));
FILE * f;
gsl_wavelet *w;
gsl_wavelet_workspace *work;
w = gsl_wavelet_alloc (gsl_wavelet_daubechies, 4);
work = gsl_wavelet_workspace_alloc (n);
f = fopen (argv[1], "r");
for (i = 0; i < n; i++)
{
fscanf (f, "%lg", &data[i]);
}
fclose (f);
gsl_wavelet_transform_forward (w, data, 1, n, work);
for (i = 0; i < n; i++)
{
abscoeff[i] = fabs (data[i]);
}
gsl_sort_index (p, abscoeff, 1, n);
for (i = 0; (i + nc) < n; i++)
data[p[i]] = 0;
gsl_wavelet_transform_inverse (w, data, 1, n, work);
for (i = 0; i < n; i++)
{
printf ("%g\n", data[i]);
}
gsl_wavelet_free (w);
gsl_wavelet_workspace_free (work);
free (data);
free (abscoeff);
free (p);
return 0;
}
</pre></div>
<p>The output can be used with the <small>GNU</small> plotutils <code>graph</code> program,
</p>
<div class="example">
<pre class="example">$ ./a.out ecg.dat > dwt.txt
$ graph -T ps -x 0 256 32 -h 0.3 -a dwt.txt > dwt.ps
</pre></div>
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