Auto-allocated RNGs

Functions that use the Designated initializers syntax for reading inputs and assigning default values use the following rules for handling RNGs.

• The first time a function is called with no gsl_rng as input, a new gsl_rng is produced. The call will effectively look like this

  static gsl_rng *internal_rng = gsl_rng_alloc(++apop_opts.rng_seed);
  

• Because internal_rng is declared static, it will remember its state as you repeatedly call the function, so you will get appropriate random numbers.

• apop_opts.rng_seed is incremented at each use, so you can write down the seed used for later reference.

• Because it increments, the next function to auto-allocate an RNG will produce different random numbers. That is, every function that uses this setup will have a different, independent RNG.

• If you would like a different outcome every time the program runs, set the seed to the time before running:

  #include <time.h>
  apop_opts.rng_seed = time(NULL);