parfor

parfor is a convenient way to distribute independent iterations of intensive computations among several "workers". One meaningful restriction is that parfor -loops cannot be nested, and invariably, that is the answer to similar questions like there and there . Why parallelization across loop boundaries is so desirable Consider the following piece of code where iterations take a highly variable amount of time on a machine that allows 4 workers. Both loops iterate over 6 values, clearly hard to share among 4. for row = 1:6 parfor col = 1:6 somefun(row, col); end end It seems like a good idea to

the code I'm dealing with has loops like the following: bistar = zeros(numdims,numcases); parfor hh=1:nt bistar = bistar + A(:,:,hh)*data(:,:,hh+1)' ; end for small nt (10). After timing it, it is actually 100 times slower than using the regular loop!!! I know that parfor can do parallel sums, so I'm not sure why this isn't working. I run matlabpool with the out-of-the-box configurations before running my code. I'm relatively new to matlab, and just started to use the parallel features, so please don't assume that I'm am not doing something stupid. Thanks! PS: I'm running the code on a quad