I did a google search for log-gamma and then browsed around the documentation. I think the issue is I was poking through the "Special Functions" and statistics functions sections, but the binomial stuff is under the "flonum" section, even though fllog-gamma can be found in "Special Functions." Maybe cross-linking them would help? And perhaps including the word "combinations" or "n choose k" somewhere in the docs for fllog-binomial would make it a bit more searchable for people who are used to different names. <div class="gmail_quote">On Wed, Feb 20, 2013 at 10:51 AM, Neil Toronto <<a href="mailto:neil.toronto@gmail.com" target="_blank">neil.toronto@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> You're welcome! A user not finding a documented function is excellent feedback. It means we need to communicate better. Do you remember how you searched for a combinations function? Neil ⊥<div class="im"> On 02/20/2013 08:45 AM, Luke Vilnis wrote: </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im"> 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 <<a href="mailto:neil.toronto@gmail.com" target="_blank">neil.toronto@gmail.com</a> </div><div><div class="h5"> <mailto:<a href="mailto:neil.toronto@gmail.com" target="_blank">neil.toronto@gmail.com</a>>> 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: </div></div> <a href="http://lists.racket-lang.org/__users" target="_blank">http://lists.racket-lang.org/__users</a> <<a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a>> </blockquote> </blockquote></div>