Re: [Boost-users] Hybrid parallelism, no more + mpi+serialization, many questions

This partly depends on how many processors/machines you have available. You need to find a way of partitioning your state space into tasks, and then doling those tasks out to processes/threads. How expensive is f()? How much memory is used? Brian On Thu, Nov 18, 2010 at 3:00 AM, Hicham Mouline wrote:

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-----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users- bounces@lists.boost.org] On Behalf Of Matthias Troyer I would go with reading once and broadcasting, especially if, as was mentioned before, one aims at going to thousands of processes. No I/O system can scale, and implementing the broadcast is trivial: a single function call.

Matthias

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The large calculation that I currently do serially and that I intend to parallelize is the maximum of the return values of a large number of evaluations of a given "function" in the mathematical sense. The number of arguments of the function is only known at runtime. Let's say it is determined at runtime that the number of arguments is 10, ie we have 10 arguments x0, ..., x9 Each argument can take a different number of values, for e.g. x0 can be x0_0, x0_1 .... x0_n0 x1 can be x1_0, x1_1, ...x1_n1 and so on...n0 and n1 are typically known at runtime and different

so serially, I run f(x0_0, x1_0, ..., x9_0) f(x0_0, x1_0, ..., x9_1) ... f(x0_0, x1_0, ..., x9_n9) then with all the x8 then all the x7 ... then all the x0. There is n0*n1*...*n9 runs Then I get the maximum of the return values.

Imagining I have N mpi processes, ideally each process would run n0*n1*...*n9/N function evaluations. How do I split?

In terms of current implementation, each of the x is a boost::variant over 4 types: a double, a pair, a triplet or a vector<double> A visitor is applied recursively to the variants in order to traverse the whole parameter space. apply_visitor on x0 => say if x0 is a triplet, then for (x0 from min to max with increment)   apply_visitor on x1 and so on until x9, then we actually call the f function with all the arguments collected so far.

How can one parallelize such a beast?

rds,

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