Also see (rationalize) to simplify my example of using ratios. I couldn't remember the name of the function off the top of my head, so I used a hacked-up-by-me version.
On Oct 12, 9:33 am, Alan <a...@malloys.org> wrote: > The JVM has no choice: it must faithfully implement the IEEE floating- > point spec (http://en.wikipedia.org/wiki/IEEE_754-2008), which > specifies limited precision. By asking it to use floats, you are > demanding that it accept rounding errors. If you want precision, there > are lots of ways to get it; the most common is to cast everything up > to integers and perform the computation there, then convert back down > later: > > user=> (def numbers [12.305 12.3049]) > #'user/numbers > user=> (/ (apply - (map #(int (* 10000 %)) numbers)) 10000) > 1/10000 > > Or you can tell Java to use BigDecimals, which have arbitrary > precision: > user=> (- 12.305M 12.3049M) > 0.0001M > > You could use clojure's excellent ratio type instead: > user=> (def nums (map #(/ % 10000) [123050 123049])) > #'user/nums > user=> nums > (2461/200 123049/10000) > user=> (apply - nums) > 1/10000 > > Computers don't lie; they just do what you tell them to. > > On Oct 12, 9:17 am, cej38 <junkerme...@gmail.com> wrote: > > > I keep running into this type of problem: > > > user=> (- 12.305 12.3049) > > 9.999999999976694E-5 > > > The computer (probably the JVM) has just lied to me. Any fourth grade > > student will know that this does not equal 0.0001. This would be less > > of a problem is the JVM was consistent; if it were consistent then the > > following equality would be true: > > > user=> (= 0.0001 (- 12.305 12.3049)) > > false > > > Now it has lied to me again! > > > I need a method to reliably compare two numbers. My first choice > > would be to have the JVM compute (- 12.305 12.3049) correctly. > > Barring that, I need a way to, without fail, compute the truthfulness > > of the following: =, <, >, <=, >=. > > -- 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
