8.5 Random Distributions

Random distributions in PDP++ are handled by an instance of the class Random. This class has a number of functions which return a random number from the distribution named by the function. Alternately the distribution can be specified in the object itself in which case the Gen() function returns a value from the specified distribution. Many of the distributions require parameters which are again either passed to the specific functions or set on the Random object itself.

Random class Variables:

Type type

Indicates the type of random variable to generate when the Gen() function is called. It can have one of the following values:

UNIFORM

A uniform distribution with var = half-range

BINOMIAL

A binomial distribution with var = p, par = n

POISSON

A Poisson distribution with var = lambda

GAMMA

A gamma distribution with var and par = stages

GAUSSIAN

A normal gaussian distribution with var

NONE

Returns the mean value

float mean

The mean of a random distribution

float var

The "variance" or rough equivalent (half-range)

float par

An extra parameter used for some distributions

Random Class Functions

float ZeroOne()

Returns a uniform random number between zero and one

float Range(float rng)

Returns a uniform random number with a given range centered at 0

float Uniform(float half_rng)

Returns a uniform random number with given half-range centered at 0

float Binom(int n, float p)

Returns a random number from a binomial distribution with n trials each of probability p

float Poisson(float l)

Returns a random number from a Poisson distribution with parameter l

float Gamma(float var, int j)

Returns a random number from a Gamma distribution with variance var and par number of exponential stages

float Gauss(float var)

Returns a gaussian (normal) random number with a variance var

float Gen()

Returns a random number using the distributions type type and the mean, var, and par variables on the Random object itself.