Thank you for your response, exactly what I was looking for. I knew I was missing something.
On Monday, July 2, 2012 5:55:49 AM UTC-7, Pierre-Henry Perret wrote: > > Hi Eric, > > The fundamental reason on that behaviour , is that Java Math library which > takes *double *as args, truncates its arguments, which is the case with > *Math.pow > .* > > From *The Joy of Clojure, sec. 4.1.1:* > __________________________________________ > (let [imadeuapi 3.14159265358979323846264338327950288419716939937M] > (println (class imadeuapi)) > imadeuapi) > ; java.math.BigDecimal > ;=> 3.14159265358979323846264338327950288419716939937M > *BUT* > (let [butieatedit 3.141592653589793*23846264338327950288419716939937*] > (println (class butieatedit)) > butieatedit) > ; java.lang.Double > ;=> 3.141592653589793 > ______________________________________________ > > So , I think the solution to your pb, seen that > *exponent = * > 9.18354961579912115600575419704879435795832466228193376178712270530013483949005603790283203125E-21M > > is to do a limited development which leads to: > *probabiblity-of-collision = exponent * > when *number-of-decimal (exponent) > 15* > > HTH > > Le samedi 30 juin 2012 08:46:10 UTC+2, Eric Scrivner a écrit : >> >> Hey All, >> >> This is more than likely a newbie question, so my apologies if this is >> not directly clojure related. >> >> I'm not sure if this is a Java or Clojure specific issue, my guess is >> both. I'm trying to do some probability calculations with both very large >> and very small numbers. The function I'm using is as follows: >> >> >>> (defn probability-of-collision [num-unique, num-generated] >>> >>> (let [exponent (.divide num-generated (.multiply 2M num-unique))] >>> >>> (.subtract 1M (.divide 1M (.pow (bigdec java.lang.Math/E) >>>> exponent))))) >>> >>> >> I would like to compute the answer for the following numbers, but only >> receive zero back: >> >> user=> (probability-of-collision (.pow 2M 132) (.pow 10M 20)) >> >> 0M >> >> >> I have tried using with-precision and several other approaches but cannot >> figure out how to get the correct value out. I was under the impression >> that BigDecimals support arbitrary precision arithmetic but perhaps I'm >> misunderstanding something? >> >> > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
