Parallel computing using Matlab

Question

I am executing windows '.exe' file in 'cmd' prompt for various inputs through Matlab. The commands as follows.

   for i = 1:n
      filename = sprintf('input_%d.dat',i);
      string = sprintf('!sfbox.exe %s', filename);
      eval(string)
   end

All input files are present and independent of each other. But if I attempt to parallelize the execution using 'parfor' as follows,

   parfor i = 1:n
      filename = sprintf('input_%d.dat',i);
      string = sprintf('!sfbox.exe %s', filename);
      eval(string)
   end

I get an error, but the code runs serially without stopping

   Explanation 

   MATLAB runs parfor loops on multiple MATLAB workers that have
   multiple workspaces. The indicated function might not access the 
   correct workspace; therefore, its usage is invalid.

Is there a correct way to execute the eval using parfor?

(PS: I tried manually executing several .exe files in cmd prompt and it is feasible to run several .exe files at same time in command prompt. Problem is the way I attempt to do it in Matlab. Please suggest better methods.)

Answer 1

You are hitting issues with Matlab not knowing what eval is actually doing. While you know that it's doing the right thing, the eval command could be executing anything. There is a little documentation on transparency issues using eval statements in parfor and spmd statements.

Switching to use an feval statement should solve your problem, as Matlab will know that the only thing going into that statement is a string. More directly, you can use the system command to directly execute an arbitrary string in the cmd prompt from matlab.

parfor i = 1:n
    filename = sprintf('input_%d.dat',i);
    string = sprintf('sfbox.exe %s', filename);
    system(string);
end