Re: Accessing results in ParallelDo
- To: mathgroup at smc.vnet.net
- Subject: [mg126103] Re: Accessing results in ParallelDo
- From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
- Date: Tue, 17 Apr 2012 06:05:14 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
I have been experimenting with parallel computing on Mathematica 8 on a two core MacBook Pro but I can't figure how to access to the results calculated in ParallelDo. Here is a a simple loop that builds a list b by appending random numbers. This runs fine and prints list b as it is generated in each of the two kernels. However, when I ask for b at the end of the loop I get b={}.
ClearAll["Global`*"];
CloseKernels[];
LaunchKernels[];
NoP = 4;
b = {};
ParallelDo[
b = Append[b, RandomInteger[{1, NoP}]];
Print["b = ", b],
{i, 1, 4}
];
Print["Final result: b=", b]
b = {4} <---kernel 2 (my annotation)
b = {3} <---kernel 1
b = {4,2} <---kernel 2
b = {3,3} <---kernel 1
Final result: b={}
My question is, how do I pass the results of ParallelDo into a variable outside the loop?
Thanks
You need to allow your variable b to be distributed between the kernels with SetSharedVariable. Try this:
ClearAll["Global`*"];
CloseKernels[];
LaunchKernels[];
SetSharedVariable[b]
b = {};
ParallelDo[
AppendTo[b, RandomInteger[{0, 10}]], {i, 1, 6}]
Print["Final result: b=", b]
Final result: b={10,10,4,10,7,7}
Have fun, Alexei
Alexei BOULBITCH, Dr., habil.
IEE S.A.
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