Ha! Sorry for not reading the documentation more thoroughly - I hope this was at least a bit educational to someone besides me :) Fantastic library and docs, by the way.
On Wed, Feb 20, 2013 at 10:38 AM, Neil Toronto <[email protected]>wrote: > On 02/20/2013 06:42 AM, Luke Vilnis wrote: > >> No problem. They should be faster even for fairly small numbers since >> they usually require the evaluation of a polynomial (an approximation of >> (log)gamma) versus repeated multiplication/division. From memory the >> code should be something like: >> >> (exp (fllog-gamma (+ 1.0 n)) - (fllog-gamma (+ 1.0 r)) - (fllog-gamma (+ >> 1.0 (- n r)))) >> >> fllog-gamma should also be faster than bflog-gamma or log-gamma if you >> don't need arbitrary precision. You're also right that this won't always >> give completely exact results - the Racket manual says that the only >> exact values are for log gamma of 1 and 2, but this usually is not a >> problem. >> >> PS. It looks like Racket's math collection has a built-in log-factorial >> function too, to avoid all the +1's, so you could try that. >> > > There's also `fllog-binomial', which computes the log number of > combinations directly. IIRC, its maximum observed error is 2 ulps. > > Neil ⊥ > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/**users <http://lists.racket-lang.org/users> >
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