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17.3 Random number generator initialization
- Function: gsl_rng * gsl_rng_alloc (const gsl_rng_type * T)
This function returns a pointer to a newly-created instance of a random number generator of type T. For example, the following code creates an instance of the Tausworthe generator,
gsl_rng * r = gsl_rng_alloc (gsl_rng_taus);
If there is insufficient memory to create the generator then the function returns a null pointer and the error handler is invoked with an error code of
GSL_ENOMEM
.The generator is automatically initialized with the default seed,
gsl_rng_default_seed
. This is zero by default but can be changed either directly or by using the environment variableGSL_RNG_SEED
(see section Random number environment variables).The details of the available generator types are described later in this chapter.
- Function: void gsl_rng_set (const gsl_rng * r, unsigned long int s)
This function initializes (or `seeds') the random number generator. If the generator is seeded with the same value of s on two different runs, the same stream of random numbers will be generated by successive calls to the routines below. If different values of s >= 1 are supplied, then the generated streams of random numbers should be completely different. If the seed s is zero then the standard seed from the original implementation is used instead. For example, the original Fortran source code for the
ranlux
generator used a seed of 314159265, and so choosing s equal to zero reproduces this when usinggsl_rng_ranlux
.When using multiple seeds with the same generator, choose seed values greater than zero to avoid collisions with the default setting.
Note that the most generators only accept 32-bit seeds, with higher values being reduced modulo 2^32. For generators with smaller ranges the maximum seed value will typically be lower.
- Function: void gsl_rng_free (gsl_rng * r)
This function frees all the memory associated with the generator r.
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