Functions and CALL Routines

RANPOI Function

Returns a random variate from a Poisson distribution.

Category:	Random Number
Tip:	If you want to change the seed value during execution, you must use the CALL RANPOI routine instead of the RANPOI function.

Syntax
Arguments
Details
Comparisons
See Also

Syntax

RANPOI(seed,m)

Arguments

seed

is a numeric constant, variable, or expression with an integer value. If seed [le] 0, the time of day is used to initialize the seed stream.

Range:	seed < 2³¹-1
See:	Seed Values for more information about seed values

m

is a numeric constant, variable, or expression that specifies the mean of the distribution.

Range:

Details

The RANPOI function returns a variate that is generated from a Poisson distribution with mean m. For m < 85, an inverse transform method applied to a RANUNI uniform variate is used (Fishman 1976) (See References). For m [ge] 85, the normal approximation of a Poisson random variable is used. To expedite execution, internal variables are calculated only on initial calls (that is, with each new m).

For a discussion about seeds and streams of data, as well as examples of using the random-number functions, see Generating Multiple Variables from One Seed in Random-Number Functions.

Comparisons

The CALL RANPOI routine, an alternative to the RANPOI function, gives greater control of the seed and random number streams.