Function pgfDpoisson.

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Description

This function calculates value of the pgf's first derivative of the Poisson distribution.

Usage

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pgfDpoisson(s, params)

Arguments

s

Value of the parameter of the pgf. It should be form interval [-1,1]. In the opposite pgf diverges.

params

Positive parameter of the Poisson distribution, such that params<-theta.

Author(s)

S. Nadarajah, B. V. Popovic, M. M. Ristic

References

Johnson N, Kotz S, Kemp A (1992) Univariate Discrete Distributions, John Wiley and Sons, New York

http://www.am.qub.ac.uk/users/g.gribakin/sor/Chap3.pdf

Examples

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params<-7
pgfDpoisson(.5,params)

## The function is currently defined as

pgfDpoisson <- function(s,params) {
   k<-s[abs(s)>1]
if (length(k)>0)
    warning("At least one element of the vector s are out of interval [-1,1]")
if (length(params)>1) stop("The length of params is 1")
    theta<-params[1]
if (theta<=0) 
    stop ("Parameter of Poisson distribution must be positive")
    theta*exp(theta*(s-1))
}

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