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Re: problem with RandomInteger

  • To: mathgroup at smc.vnet.net
  • Subject: [mg112206] Re: problem with RandomInteger
  • From: Albert Retey <awnl at gmx-topmail.de>
  • Date: Sat, 4 Sep 2010 04:02:46 -0400 (EDT)
  • References: <i5qhhg$pkm$1@smc.vnet.net>

Am 03.09.2010 12:09, schrieb Yuri Izrailsky:
> Hello Mathgroup,
> 
>   I have recently encountered a strange behavior of RandomInteger
> function when used inside Module construct. Here is an example:
> 
> str1[] := Module[{l, i, j},
>   l = {0, 0, 0};
>   i = RandomInteger[{1, 3}];
>   l[[i]] = 1;
>   j = RandomInteger[{1, 3}];
>   l[[j]]
>   ]
>   
> In[3]:= N[Total[Table[str1[],{200}]]]/200
> Out[3]= 0.345
> 
> which is reasonably close to 1/3, but
> 
> In[5]:= N[Total[Table[str1[],{1000}]]]/1000
> Out[5]= 0.997
> 
> looks very strange. What's happening here?

I think this is because Table does compile if it thinks that will
improve speed. You can change the limit when this will start, e.g.:

SetSystemOptions["CompileOptions" -> "TableCompileLength" -> 100000];

now

N[Total[Table[str1[], {10000}]]]/10000

will return the expected result. I don't exactly understand why this
goes wrong when compiling, but I think it is a bug...

hth,

albert


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