18.5 Auxiliary random number generator functions

The following functions provide information about an existing generator. You should use them in preference to hard-coding the generator parameters into your own code.

Function: const char * gsl_rng_name (const gsl_rng * r)

This function returns a pointer to the name of the generator. For example,

printf ("r is a '%s' generator\n", 
        gsl_rng_name (r));

would print something like r is a 'taus' generator.

Function: unsigned long int gsl_rng_max (const gsl_rng * r)

gsl_rng_max returns the largest value that gsl_rng_get can return.

Function: unsigned long int gsl_rng_min (const gsl_rng * r)

gsl_rng_min returns the smallest value that gsl_rng_get can return. Usually this value is zero. There are some generators with algorithms that cannot return zero, and for these generators the minimum value is 1.

Function: void * gsl_rng_state (const gsl_rng * r)

Function: size_t gsl_rng_size (const gsl_rng * r)

These functions return a pointer to the state of generator r and its size. You can use this information to access the state directly. For example, the following code will write the state of a generator to a stream,

void * state = gsl_rng_state (r);
size_t n = gsl_rng_size (r);
fwrite (state, n, 1, stream);

Function: const gsl_rng_type ** gsl_rng_types_setup (void)

This function returns a pointer to an array of all the available generator types, terminated by a null pointer. The function should be called once at the start of the program, if needed. The following code fragment shows how to iterate over the array of generator types to print the names of the available algorithms,

const gsl_rng_type **t, **t0;

t0 = gsl_rng_types_setup ();

printf ("Available generators:\n");

for (t = t0; *t != 0; t++)
  {
    printf ("%s\n", (*t)->name);
  }