Perhaps the problem is in withSystemRandom, which uses unsafePerformIO? Does the problem persist if you seed your program with some predefined seed?
Roman * Azeem -ul-Hasan <aze...@live.com> [2013-03-16 13:46:54+0500] > > Hi Carter, > > Thank you for your help, but I can confirm that this is not due to > floating point errors. My own hunch is that it is due to the way I am using > random number generation from System.Random.MWC. To check it I wrote a > version of mkNetwork function using random number generation from > System.Random and it works fine with optimizations turned on. So any ideas > why optimizations are messing with System.Random.MWC? > > Azeem > From: carter.schonw...@gmail.com > Date: Fri, 15 Mar 2013 17:09:36 -0400 > Subject: Re: [Haskell-cafe] Optimization flag changing result of code > execution > To: aze...@live.com > CC: haskell-cafe@haskell.org > > Hey Azeem,have you tried running the same calculation using rationals? Theres > some subtleties to writing numerically stable code using floats and doubles, > where simple optimizations change the orders of operations in ways that > *significantly* change the result. In this case it looks like you're > averaging the averages, which i *believe* can get pretty nasty in terms of > numerical precision. Rationals would be a bit slower, but you could then > sort out which number is more correct. > > > > On Fri, Mar 15, 2013 at 4:07 PM, Azeem -ul-Hasan <aze...@live.com> wrote: > > > > > > I was trying to solve a computational problem form James P Sethna's book > Statistical Mechanics: Entropy, Order Parameters, and Complexity[1]. The > problem is on page 19 of the pdf linked and is titled Six degrees of > separation. For it I came up with this code: http://hpaste.org/84114 > > > > It runs fine when compiled with -O0 and consistently yields an answer around > 10, but with -O1 and -O2 it consistently gives an answer around 25. Can > somebody explain what is happening here? > > > > [1] > http://pages.physics.cornell.edu/~sethna/StatMech/EntropyOrderParametersComplexity.pdf > > > > Azeem > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe@haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
