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. ZAE Weiergewan, 11, rue Edmond Reuter, L-5326 Contern, LUXEMBOURG Office phone : +352-2454-2566 Office fax: +352-2454-3566 mobile phone: +49 151 52 40 66 44 e-mail: alexei.boulbitch at iee.lu