Parfor code runs slower on 16 core, 2.3 GHz AMD processor than 4 core, 3.3 GHz Intel processor

Hello everyone,

For some reason, the following code runs about twice as fast on a desktop with a 4 core, 3.3 GHz Intel processor than on a node on a computing cluster with a 16 core, 2.3 GHz AMD processor (don't know the full specs for either). Either way, a parfor loop is faster on both computers than a regular for loop, but I can't see how 16 cores could be slower than 4 cores. I am compiling the code using mcc beforehand in each case, and the correct number of workers are used.

Thank you in advance for your help!

parfor ii = 1:indexer

   [output1,output2] = simulate_ssa((initial_condition(ii,:)), timestep, final_time_step,ii);

%Writes a file out to the current working directly (using the index ii to avoid rewriting over a previous file) and runs a unix command on that file

   if output1 == 2 
      finaloutputA = vertcat(finaloutputA,[output2,initial_condition(ii,end)]);
   else
      finaloutputB = vertcat(finaloutputB,[output2,initial_condition(ii,end)]);
   end

 end