slow Matlab on Ubuntu LTS and ZERO Swap

I was using Matlab2012 under Win7 and my algorithm was consuming a huge amount of memory though it was fast (80 seconds for one iteration). Now I am using Matlab2013 under Ubuntu 12.04 LTS and though the usage of the RAM is very small, but the time is extremely higher than it was on windows (30 minutes for the iteration and not finished untill now). As I said the RAM is showing a usage of 1G out of 8G ...while the swap is showing 0% of 8G. I checked the default value and it is 60, but not used by anyhow!! What might be the problem, and how to speed up Matlab the way it was before?