Parallel Code

Hi

Can I run this code in parallel?

A1=F(A1,B1)

A2=F(A2,B2)

F is a function, A1 B1 are unrelated to A2 B2

How can I do this ? ( now it runs one after the other)

Thanks

Shani

Answer 1

[Edric Ellis]

If you have Parallel Computing Toolbox, you could do this:

    % first start up 2 local workers
    matlabpool open local 2

    % Make cell arrays of inputs
    Ain = {A1, A2}; Bin = {B1, B2};

    parfor ii=1:2
        % Return outputs as a cell array
        Aout{ii} = F(Ain{ii}, Bin{ii});
    end

[hamid]

thanks edric

i write your above code and suppose function F do this compute

Aout(ii)=Ain(ii)*rand+Bin(ii)*rand

but in every run i get same answer.why when i use two rand always i get same output? even when i use spmd both in every run i get same answers.

please say why this occur.

blessing

[Edric Ellis]

Just like MATLAB itself, parallel workers start up in a deterministic random state as described in the documentation. That page also tells you how you can control this state.

[hamid]

excuse me i can not understand mr.edric. i ask my question again with a example. i write function f that return a random number and a script with the name of spmdtest. in spmdtest i want run function f in parallel.

my question is that why in every run i see same output? at first run output was lab1: c=.9713 lab2 c=.2951 and in second run again output was lab1: c=.9713 lab2 c=.2951 and in every run output is this. while i think,in every run i should get different output.

please explain what is this problem. and how i can solve it. and this is need that to say i visit above link that you put, but i cannt understand how i can slove my problem and in my matlab verson 2010 there is no function with name parpool. thanks

function [ c ] = F(  )
c=rand
end

matlabpool open
spmd(2)
    F();
end
matlabpool close

[Edric Ellis]

You should not open and close the pool each time - you should open the pool once and leave it open. Each time the pool opens, you are creating new workers with a fresh random number generator state.

[hamid]

oh yes. thank you. now i can do my work

god bless you