Parallel code is taking longer time than sequential code using Parallel computing toolbox in MATLAB. Why?

Question

I am working with MATLAB. I am just new with parallel computing toolbox in MATLAB. I have core i3 processor, MATLAB R2011a, 2 GB of RAM, 320 Hard disk.

To calculate speed up, I just wrote following code and found that parallel code is taking longer time than a sequential code.

1st code is taking 0.039763 seconds

2nd code is taking 0.379056 seconds .

---

1st code:

tic
MM = magic(5);
MN = magic(5);
ML = magic(5);
MP = magic(5);
MK = magic(5);
MM
MN
ML
MP
MK
toc

2nd Code:

matlabpool open local 4

tic
spmd  % Uses all 3 workers
    MM = magic(5); % MM is a variable on each lab
end
MM{1}
MM{2}
MM{3}
MM{4}
toc
matlabpool close

I want to learn parallel computing toolbox.

Answer 1

As mentioned by Dan in the comments, the problem is clearly too small for parallelization to be beneficial. Increasing for example the size of the magic matrices you create from 5 to 5000, already shows a clear improvement. That is, with the larger size the overhead of parallelization becomes (almost) negligible compared to the computation time for one matrix.