The seed of the random number generator can be set as follows:
default = off)
Indicates whether a user-set seed should be used every time the
Pythia::init routine is called. If off, the random number
generator is initialized with its default seed at the beginning
of the run, and never again. If on, each new
call (should several be made in the same run) results in the random
number being re-initialized, thereby possibly starting over with the
same sequence, if you do not watch out.
default = -1;
maximum = 900000000)
The seed to be used, if
setSeed is on.
A negative value gives the default seed,
a value 0 gives a random seed based on the time, and
a value between 1 and 900,000,000 a unique different random number
For more on random numbers see here.
This includes methods to save and restore the state of the generator,
and some preprogrammed methods to generate non-uniform random numbers.