Re: problem with RandomInteger

*To*: mathgroup at smc.vnet.net*Subject*: [mg112217] Re: problem with RandomInteger*From*: Peter Pein <petsie at dordos.net>*Date*: Sun, 5 Sep 2010 05:27:17 -0400 (EDT)*References*: <i5qhhg$pkm$1@smc.vnet.net>

Am Sat, 4 Sep 2010 08:02:36 +0000 (UTC) schrieb Albert Retey <awnl at gmx-topmail.de>: ... > 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 > Indeed! Using a compiled version of str1[], there is no chance to get reliable results: In[1]:= strC = Compile[{}, Module[{l, i, j}, l = {0, 0, 0}; i = RandomInteger[{1, 3}]; l[[i]] = 1; j = RandomInteger[{1, 3}]; l[[j]]], {{i | j, _Integer}, {l, _Integer, 1}}]; In[2]:= N[Total[Table[strC[], {10}]]]/10 Out[2]= 1. In[3]:= N[Total[Table[strC[], {1000}]]]/1000 Out[3]= 1. In[4]:= N[Total[ParallelTable[strC[], {1000}]]]/1000 Out[4]= 1. But this gives the expected result: In[1]:= simp=Compile[{{n,_Integer}},Sum[Boole[RandomInteger[{1,3}]===2],{n}]/n//N]; In[2]:= simp/@(10^{1,2,3,4}) Out[2]= {0.3,0.36,0.34,0.3386} Can anyone from Wolfram Inc. please explain this behaviour? TIA, Peter