Re: How to Compile this code (multiple random walks)
- To: mathgroup at smc.vnet.net
- Subject: [mg118090] Re: How to Compile this code (multiple random walks)
- From: Derek Yates <yatesd at me.com>
- Date: Tue, 12 Apr 2011 05:56:30 -0400 (EDT)
- References: <inuncc$2dl$1@smc.vnet.net>
To my knowledge NestWhileList is not compilable, so I am surprised
that you say it worked for a single counter. You may need to use
SetSystemOptions["CompileOptions"->"CompileReportExternal"->True] to
get a warning message about not being able to compile.
There is a work around for NestWhileList. FixedPointList is
compilable, and by using the option SameTest carefully, you can
replicate the NestWhileList behaviour. Here is some code that appears
to compile properly (using Mathematica 8) and does most of what you
want in compiled form. The final counter for the number of steps is
not compiled. The code below is also slightly more general than yours,
in that it uses the length of the input (start) vector to decide how
many random walk counters there are.
With[{compiledfunc=Compile[{{start,_Real,1}},
Most@FixedPointList[#+(If[#<0.5,-1,1]&)/
@RandomReal[{0,1},Length[start]]&,start,
SameTest-
>(Module[{b=False},Scan[If[Not[-5.<#<5.],Return[b=True]]&,#];b]&)]]},
f[start_]:=Transpose[{Range[0,Length[#]-1],#}]&@compiledfunc[start]]
I don't know of any way to include the path counter into the compile
as the result you generate is not a tensor. If you are planning to use
the code in Mathematica, then I doubt the performance hit of not
having that last step in the Compile will be very great. If you are
wanting to compile it to C code, then you probably need to think of a
different format to return the results.