dppois: Stable evaluation of difference between Poisson c.d.f.s

In mgcv: Mixed GAM Computation Vehicle with Automatic Smoothness Estimation

Stable evaluation of difference between Poisson c.d.f.s

Description

Evaluates the difference between two Poisson cumulative distribution functions avoiding cancellation error.

Usage

dppois(y0,y1,mu,log.p=TRUE)

Arguments

y0	vector of lower values at which to evaluate Poisson distribution function.
y1	vector of upper values at which to evaluate Poisson distribution function.
mu	vector giving Poisson means
log.p	set to FALSE to compute on probability scale.

Details

Equivalent to log(ppois(y1,mu)-ppois(y0,mu)), but stable when y0 and y1 are highly improbable and in the same tail of the distribution (avoids cancellation to log(0)).

Author(s)

Simon N. Wood [e-mail]

Examples

require(mgcv)
n <- 10
mu <- rep(2,n)
y0 <- c(0:5,10,23,0,2)
y1 <- c(1:6,11,1000,100,40)
dppois(y0,y1,mu)
log(ppois(y1,mu)-ppois(y0,mu))

mgcv documentation built on Nov. 7, 2025, 5:06 p.m.