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<title>GNU Scientific Library &ndash; Reference Manual: Example programs for vectors</title>

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<a name="Example-programs-for-vectors"></a>
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<p>
Previous: <a href="Vector-properties.html#Vector-properties" accesskey="p" rel="previous">Vector properties</a>, Up: <a href="Vectors.html#Vectors" accesskey="u" rel="up">Vectors</a> &nbsp; [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Example-programs-for-vectors-1"></a>
<h4 class="subsection">8.3.11 Example programs for vectors</h4>

<p>This program shows how to allocate, initialize and read from a vector
using the functions <code>gsl_vector_alloc</code>, <code>gsl_vector_set</code> and
<code>gsl_vector_get</code>.
</p>
<div class="example">
<pre class="verbatim">#include &lt;stdio.h&gt;
#include &lt;gsl/gsl_vector.h&gt;

int
main (void)
{
  int i;
  gsl_vector * v = gsl_vector_alloc (3);
  
  for (i = 0; i &lt; 3; i++)
    {
      gsl_vector_set (v, i, 1.23 + i);
    }
  
  for (i = 0; i &lt; 100; i++) /* OUT OF RANGE ERROR */
    {
      printf (&quot;v_%d = %g\n&quot;, i, gsl_vector_get (v, i));
    }

  gsl_vector_free (v);
  return 0;
}
</pre></div>

<p>Here is the output from the program.  The final loop attempts to read
outside the range of the vector <code>v</code>, and the error is trapped by
the range-checking code in <code>gsl_vector_get</code>.
</p>
<div class="example">
<pre class="example">$ ./a.out
v_0 = 1.23
v_1 = 2.23
v_2 = 3.23
gsl: vector_source.c:12: ERROR: index out of range
Default GSL error handler invoked.
Aborted (core dumped)
</pre></div>

<p>The next program shows how to write a vector to a file.
</p>
<div class="example">
<pre class="verbatim">#include &lt;stdio.h&gt;
#include &lt;gsl/gsl_vector.h&gt;

int
main (void)
{
  int i; 
  gsl_vector * v = gsl_vector_alloc (100);
  
  for (i = 0; i &lt; 100; i++)
    {
      gsl_vector_set (v, i, 1.23 + i);
    }

  {  
     FILE * f = fopen (&quot;test.dat&quot;, &quot;w&quot;);
     gsl_vector_fprintf (f, v, &quot;%.5g&quot;);
     fclose (f);
  }

  gsl_vector_free (v);
  return 0;
}
</pre></div>

<p>After running this program the file <samp>test.dat</samp> should contain the
elements of <code>v</code>, written using the format specifier
<code>%.5g</code>.  The vector could then be read back in using the function
<code>gsl_vector_fscanf (f, v)</code> as follows:
</p>
<div class="example">
<pre class="verbatim">#include &lt;stdio.h&gt;
#include &lt;gsl/gsl_vector.h&gt;

int
main (void)
{
  int i; 
  gsl_vector * v = gsl_vector_alloc (10);

  {  
     FILE * f = fopen (&quot;test.dat&quot;, &quot;r&quot;);
     gsl_vector_fscanf (f, v);
     fclose (f);
  }

  for (i = 0; i &lt; 10; i++)
    {
      printf (&quot;%g\n&quot;, gsl_vector_get(v, i));
    }

  gsl_vector_free (v);
  return 0;
}
</pre></div>





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