Returning very large numbers

[choijos]

I am trying to run a function that outputs a very large number. The problem is that the return says inf.
The function is as follows:

comb.prob <- function(n){
choose(2000,n)*choose(28000,(300-n))/choose(30000,300)
}

However If I reduce my input numbers by 1/10, R returns a value to me.

Eg.

comb.prob <- function(n){
choose(200,n)*choose(2800,(30-n))/choose(3000,30)
}

I was wondering if there was a way to boost R’s computing power or another method so I could get R to run the first equation?

[StatSteph]

You might want to try using the log version of choose (lchoose). I show an example with smaller numbers that these are equivalent.

Using some log identities, namely that log(a*b/c)=log(a)+log(b)-log(c)

comb.prob.log <- function(n){
  exp(lchoose(2000,n)+lchoose(28000,(300-n))-lchoose(30000,300))
}


n <- 2
exp(lchoose(20,n)+lchoose(280,(3-n))-lchoose(300,3))
#> [1] 0.01194137
choose(20,n)*choose(280,(3-n))/choose(300,3)
#> [1] 0.01194137

^{Created on 2022-07-20 by the reprex package (v2.0.1)}

[choijos]

Thank you for your reply! It seemed to do the trick.

Josh