Have you tried the Profiler tool with your code? This can quickly highlite which parts take the most time. In this case line 24 of population.m uses quite a bit of the time. It is always recommended to create vectors with the desired size at the beginning instead of adding to its size on each iteration of a loop. The rand function also accepts size arguments and this will execute much faster than pulling scalar random numbers one by one.
x = zeros(N, 1);
rvalues = rand(N,1);
