This example is what you're looking for: http://www.vertex42.com/ExcelArticles/mc/MatlabMCExample.html
MC is computationally heavy. For this example taken from the link I repeat the procedure 100,000 times drawing samples of 1000. It takes 13 seconds using very low amount of memory.
In MC in general the more you have the better, thus you could optimize this example to generate rand(n,something) to fit the 80% of your memory and reduce the number of loops.
tic
n = 1000;
l = 1e5;
s.ymean = zeros(n,1);
s.ystd = s.ymean;
for ii = 1:l
x1 = randn(n,1) * 5 + 100;
x2 = rand (n,1) * 10 + 5;
y = x2.^2 ./ x1;
s.ymean(ii) = mean(y);
s.ystd (ii) = std(y);
end
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