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<title>DWT Examples - GNU Scientific Library -- Reference Manual</title>
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<p>
Next: <a rel="next" accesskey="n" href="DWT-References.html">DWT References</a>,
Previous: <a rel="previous" accesskey="p" href="DWT-Transform-Functions.html">DWT Transform Functions</a>,
Up: <a rel="up" accesskey="u" href="Wavelet-Transforms.html">Wavelet Transforms</a>
<hr>
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<h3 class="section">31.4 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.
<pre 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)
{
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></pre>
<p class="noindent">The output can be used with the <span class="sc">gnu</span> plotutils <code>graph</code> program,
<pre class="example"> $ ./a.out ecg.dat > dwt.dat
$ graph -T ps -x 0 256 32 -h 0.3 -a dwt.dat > dwt.ps
</pre>
<hr>The GNU Scientific Library - a free numerical library licensed under the GNU GPL<br>Back to the <a href="/software/gsl/">GNU Scientific Library Homepage</a></body></html>
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