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<title>Example programs for vectors - GNU Scientific Library -- Reference Manual</title>
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<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>.
<pre class="example"><pre class="verbatim"> #include <stdio.h>
#include <gsl/gsl_vector.h>
int
main (void)
{
int i;
gsl_vector * v = gsl_vector_alloc (3);
for (i = 0; i < 3; i++)
{
gsl_vector_set (v, i, 1.23 + i);
}
for (i = 0; i < 100; i++) /* OUT OF RANGE ERROR */
{
printf ("v_%d = %g\n", i, gsl_vector_get (v, i));
}
gsl_vector_free (v);
return 0;
}
</pre></pre>
<p class="noindent">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>.
<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>
<p class="noindent">The next program shows how to write a vector to a file.
<pre class="example"><pre class="verbatim"> #include <stdio.h>
#include <gsl/gsl_vector.h>
int
main (void)
{
int i;
gsl_vector * v = gsl_vector_alloc (100);
for (i = 0; i < 100; i++)
{
gsl_vector_set (v, i, 1.23 + i);
}
{
FILE * f = fopen ("test.dat", "w");
gsl_vector_fprintf (f, v, "%.5g");
fclose (f);
}
gsl_vector_free (v);
return 0;
}
</pre></pre>
<p class="noindent">After running this program the file <samp><span class="file">test.dat</span></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:
<pre class="example"><pre class="verbatim"> #include <stdio.h>
#include <gsl/gsl_vector.h>
int
main (void)
{
int i;
gsl_vector * v = gsl_vector_alloc (10);
{
FILE * f = fopen ("test.dat", "r");
gsl_vector_fscanf (f, v);
fclose (f);
}
for (i = 0; i < 10; i++)
{
printf ("%g\n", gsl_vector_get(v, i));
}
gsl_vector_free (v);
return 0;
}
</pre></pre>
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