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Re: Faster Random Walk Simulation ?!?


mfific at gmail.com wrote:

> Dear All,
> I am running a simulation with Mathematica 5 that includes random walk
> described below. The argument boundaryA is upper and lower boundary for
> a random walk. Parameter "value" is just a constant arbitrarily set to
> 0.5. The output of the table function is the 10000 random walks, and
> their path to either +5 or -5 boundary value.
> While everything works as expected, it takes considerable duration of
> time. For example it takes 2.6 seconds to generate the table output, on
> a relatively fast computer.
> 
> I would very appreciate if any significantly faster solution could be
> suggested.
> 
> 
> value = .5
> 
> 
> RandomWalk[boundaryA_] := Block[{l = {{0, 0}}, x = 0,
>   i = 0 }, While[boundaryA > x > -boundaryA,
>        x += If[Random[] > value, 1, -1];
>       l = Append[l, {++i, x}]];
>     l]
> 
> Timing[Table[RandomWalk[5], {i, 1, 10000}];]
> 
> Out[420]=
> {2.672 Second, Null}
> 
> 
> Thank you very much,
> 
> Mario Fific
> 
> 
> Mario Fific
> Cognitive Psychology, Cognitive Science
> Indiana University
> 1101 E. 10th St.
> Bloomington, IN  47405-7007
> 

Does this help?

cf = Compile[
   {{value, _Real}, {bound, _Integer}},
  Transpose[{Range[0, Length[#] - 1], #}]& @
   NestWhileList[
    # + If[Random[] > value, 1, -1]&,
    0,
   -bound < # < bound&]
  ]

--Mark.


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