POISSONPDF Function

Evaluates the probability function of a Poisson random variable.

Usage

result = POISSONPDF (k, theta)

Input Parameters

k—Argument for which the Poisson distribution function is to be evaluated.

theta—Mean of the Poisson distribution. theta must be positive.

Returned Value

result—The probability that a Poisson random variable takes a value equal to k.

Input Keywords

Double—If present and nonzero, double precision is used.

Discussion

POISSONPDF evaluates the probability function of a Poisson random variable with parameter theta. theta, which is the mean of the Poisson random variable, must be positive. The probability function (with q = theta) is:

 

POISSONPDF evaluates this function directly, taking logarithms and using the log gamma function.

Example

Suppose X is a Poisson random variable with q = 10. In this example, we evaluate the probability function at k = 7.

result = POISSONPDF(7, 10.0)

PRINT, "The probability that X is equal to 7 is:"

PRINT, result, Format='(F9.7)'

; PV-WAVE prints the following:

; The probability that X is equal to 7 is:

; 0.0900792