The function `rand()` produces a sequence of pseudo-random numbers between 0 and 1 using an algorithm from P. L'Ecuyer and S. Cote, "Implementing a random number package with splitting facilities", ACM Transactions on Mathematical Software, 17:98-111 (1991).
rand(0) returns a pseudo random number in the interval [0:1] generated from the current value of two internal 32-bit seeds. rand(-1) resets both seeds to a standard value. rand(x) for integer 0 < x < 2^31-1 sets both internal seeds to x. rand({x,y}) for integer 0 < x,y < 2^31-1 sets seed1 to x and seed2 to y.