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8.3.11 Example programs for vectors

This program shows how to allocate, initialize and read from a vector using the functions gsl_vector_alloc, gsl_vector_set and gsl_vector_get. 

#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;
}

Here is the output from the program. The final loop attempts to read outside the range of the vector v, and the error is trapped by the range-checking code in gsl_vector_get. 

$ ./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)

The next program shows how to write a vector to a file. 

#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;
}

After running this program the file test.dat should contain the elements of v, written using the format specifier %.5g. The vector could then be read back in using the function gsl_vector_fscanf (f, v) as follows: 

#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;
}