Re: Troubling Bug involving RandomReal, NestList, and Table
- To: mathgroup at smc.vnet.net
- Subject: [mg86261] Re: Troubling Bug involving RandomReal, NestList, and Table
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Fri, 7 Mar 2008 02:27:21 -0500 (EST)
- References: <fqo8tn$t2o$1@smc.vnet.net>
Hi,
this is a bug when Mathematica "Compile" the expression
in Table[] try
opts = "CompileOptions" /. SystemOptions[];
opts = opts /. ( "TableCompileLength" -> _) :> (
"TableCompileLength" -> Infinity);
SetSystemOptions["CompileOptions" -> opts];
and the bug disappear.
Regards
Jens
jwmerrill at gmail.com wrote:
> When making tables of 250 or more directions, Mathematica seems to
> forget how to do arithmetic. I realize these "random" directions are
> not properly uniform, but that's beside the point.
>
> $Version
>> "6.0 for Mac OS X x86 (32-bit) (April 20, 2007)"
>
> randomDirection3[] :=
> NestList[Sqrt[1 - #^2] &, RandomReal[], 1]
>
> ListPlot[Table[randomDirection3[], {249}], AspectRatio -> Automatic]
> ListPlot[Table[randomDirection3[], {250}], AspectRatio -> Automatic]
>
>> [Graphs you'll need to generate for yourself]
>
> Variance[Table[Norm[randomDirection3[]], {249}]]
> Variance[Table[Norm[randomDirection3[]], {250}]]
>
>> 1.49104*10^-33
>> 0.0513843
>
> What!?!
>
> Jason Merrill
>