How can i run 2 functions in parallel with MATLAB parallel Computing Toolbox? looking for an easy example code!

Hey people,

i have already implemented several smaller issues with Matlab. Now i have to face a real challenge i cannot solve so far. Its about parallel computing a thing i have no experience with yet. I'd be glad if somebody with some experience about parallel computing could give me some kind of example code. i am sure i can make it with some support but i havent found anything like that on the internet yet. i just would like to run 2 functions in parallel, more exact my goal is to realize the following pseudocode:

while (termination criterion is not met)

  Activate Function_I
  Activate Function_II

  while(Function_I or Function_II are active)

    if (Function_I or Function_II produce a new best solution)

    kill Function_I and Function_II

    end if

  end while

end(while)

plz give me some hints how to realize it! id be very glad. i am working with MATLAB R2010b

Thanks a lot!

Answer 1

[Edric Ellis]

In R2010b, your options are to use either parfor or spmd. (In R2013b and later, there's parfeval which gives more flexibility, but is a little more difficult to use). With either parfor or spmd, you will need to arrange so that your two functions can make a partial attempt at a solution, and then continue - this is because you need to check whether either has completed yet. This will necessarily make things less efficient. You might do something like this:

parpool(2);
spmd
  done = false;
  state = []; % state used by Function_I or Function_II
  while ~done
    % Run Function_I/Function_II for a while
    if labindex == 1
      [state, gotSolution] = Function_I(state);
    elseif labindex == 2
      [state, gotSolution] = Function_II(state);
    end

      % Check to see if either has completed using GOP which
      % combines the results of 'gotSolution' from each lab
      done = gop(@any, gotSolution);
    end
  end

% access solution in 'state'

In R2013b and later, you could simply use parfeval to invoke Function_I / Function_II and then use fetchNext to work out when one of them has completed, a bit like this:

parpool(2);
f1 = parfeval(@Function_I, 1);
f2 = parfeval(@Function_II, 1);
% fetchNext waits for one of the functions to complete,
% and also gets the result
[idx, result] = fetchNext([f1, f2]);
% We're done, so we can cancel f1 and f2 (one will actually already be complete)
cancel([f1, f2]);

[Shubham Jha]

Can u justify what is 'state' here? As because I am facing problem in calling my Function_I & Function_II. There are arguments needed to be passed with these functions. So 8th and 10th lines of your first solution show syntactical errors.

I am doing like this:- Function_I: subalgo1(A,C,n) Function_II: subalgo2(A,C,n)

parpool(2);
spmd
done = false;
state = []; % state used by Function_I or Function_II
while ~done
  % Run Function_I/Function_II for a while
  if labindex == 1
    [state, gotSolution] = subalgo1(A,C,n)(state);
  elseif labindex == 2
    [state, gotSolution] = subalgo2(A,C,n)(state);
  end
    % Check to see if either has completed using GOP which
    % combines the results of 'gotSolution' from each lab
    done = gop(@any, gotSolution);
  end
end