The modified function I presented contains a stupid error, which is 
corrected below.

sum1 <- function(l,u,t,i,n,w,tol=.Machine$double.xmin) {
v <- 0
v2 <- 1
for (m in 0 :w & v2 > tol) {
 v1 <- ((u^(1/2))*(l^(1/2))*t)^(i-n+2*m)
 v2 <- exp(-lgamma(i-n+m+1)-lgamma(m+1))
 v3 <- v1*v2
 v <- v+v3
 }
return(v)
}

sum1(1,2,10,80,3,80)
[1] 5.519201e-23
> sum1(1,2,10,80,3,100)
[1] 6.892307e-23
> sum1(1,2,10,80,3,200)
[1] 1.375784e-22
> sum1(1,2,10,80,3,1000)
[1] 6.86821e-22


Need more coffee...

Joseph F. Lucke
Senior Statistician
Research Institute on Addictions
University at Buffalo
State University of New York
1021 Main Street
Buffalo, NY  14203-1016
Office: 716-887-6807
Fax:     716-887-2510
http://www.ria.buffalo.edu/profiles/lucke.html

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