15.5.475 random

random( [seed=seed, period=period,] [dimensions] [, /uniform, /normal, /sample, /shuffle, /bits])

Returns an array with the specified dimensions (which must be a set of scalars and/or arrays) filled with pseudo-random numbers. The keywords determine the distribution. If no keyword is specified, then /uniform is assumed.

/uniform

selects a uniform distribution. If period is also specified, then long numbers between 0 and period - 1 (inclusive) are returned. If period is not also specified, then float numbers between 0 and 1 (exclusive of the endpoints) are returned.

/normal

selects a normal distribution with zero mean and unit standard deviation.

/sample

selects a uniform distribution between 0 and period - 1 (inclusive), but the numbers are in ascending order and no number appears more than once.

/shuffle

selects a uniform distribution between 0 and period - 1 (inclusive), but no number appears more than once and they are in random order.

/bits

selects byte 0s and 1s with equal probability.

seed is an integer seed number for the random number generation: if you specify the same seed, then you get the same sequence of random numbers. There is one seed for /bits and one independent seed for the other distributions. The initial seed is 123459876 for /bits and -123459876 for the other distributions. You may specify a seed and no dimensions in calls to random or any of its cousins. It that case, the seed is set to the specified value, and a scalar 1 is returned.

There are several separate routines that correspond to random with a particular distribution.

The pseudo-random numbers generated when /bits is selected follow from a primitive polynomial modulo 2 with a period of 2^31 - 1, or about 2.1e9.

The method used to generate the pseudo-random numbers with other distributions is Matsumoto and Nishimura’s “Mersenne Twister” mt19937 generator. The period of this generator is 2^19937 - 1, or about 1e6000.

See also: randomb, randomn, randomu, Random Arrays