12.5 Examples

The following example shows how to use the permutation p to print the elements of the vector v in ascending order,

     gsl_sort_vector_index (p, v);
     
     for (i = 0; i < v->size; i++)
     {
         double vpi = gsl_vector_get (v, p->data[i]);
         printf ("order = %d, value = %g\n", i, vpi);
     }

The next example uses the function gsl_sort_smallest to select the 5 smallest numbers from 100000 uniform random variates stored in an array,

     #include <gsl/gsl_rng.h>
     #include <gsl/gsl_sort_double.h>
     
     int
     main (void)
     {
       const gsl_rng_type * T;
       gsl_rng * r;
     
       size_t i, k = 5, N = 100000;
     
       double * x = malloc (N * sizeof(double));
       double * small = malloc (k * sizeof(double));
     
       gsl_rng_env_setup();
     
       T = gsl_rng_default;
       r = gsl_rng_alloc (T);
     
       for (i = 0; i < N; i++)
         {
           x[i] = gsl_rng_uniform(r);
         }
     
       gsl_sort_smallest (small, k, x, 1, N);
     
       printf ("%d smallest values from %d\n", k, N);
     
       for (i = 0; i < k; i++)
         {
           printf ("%d: %.18f\n", i, small[i]);
         }
     
       free (x);
       free (small);
       gsl_rng_free (r);
       return 0;
     }

The output lists the 5 smallest values, in ascending order,

     $ ./a.out
     5 smallest values from 100000
     0: 0.000003489200025797
     1: 0.000008199829608202
     2: 0.000008953968062997
     3: 0.000010712770745158
     4: 0.000033531803637743