On Sun, 28 Sep 2008, J?rg Gro? wrote:
Hi,
I tried to calculate the formula for the birthday problem
(the probability that at least two people out of a group of n people share
the same birthday)
But the factorial-function allows me only to calculate factorials up to 170.
You might want to look at the pbirthday() and qbirthday() functions and
the examples on their help page. The function implements Diaconis &
Mosteller's approximation, which works for different values of two as well
as of n and 365. One of the examples compares to the exact calculation,
which it computes as x2<- 1-sapply(10:100,
function(n)prod((365:(365-n+1))/rep(365,n)))
This is obviously slow compared to the formula with factorials, but it
does only take two milliseconds on my laptop, so it's not *that* slow. The
phrase "premature optimization" springs to mind.
-thomas______________________________________________
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