[R] further to my last email

[Prof Brian D Ripley]

On Fri, 14 Dec 2001, Cowpertwait, Paul wrote:

> .. the round function seems to get round it (excuse the pun):
>
> > round(gamma(21)/(gamma(6)*gamma(16))) == round(choose(20,5))
> [1] TRUE
>
> So I presume the problem is related to gamma being a real function.
> However, I'm still not sure why there's a break from TRUE to FALSE for
> certain values.  Any comments would be appreciated!

It's rounding error:  == is *not* a sensible way to compare real numbers.
Use all.equal(), for example.

BTW, these numbers get large quite rapidly.  Use lgamma to do the
calculations on log scale is safer.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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