What is the problem you want to solve? Matlab creates new data in each iteration by:
The former values are not needed anymore, but a garbage collection would need some time. Therefore it is possible that Matlab waits until collecting free memory is required and until then is seems like the used memory is growing, but it is only the part, which has not been declared as free. So I assume, that there is no problem at all.
By the way, the subplot 131 style is outdated since Matlab 5.3 - for 20 years now. It is time to use the modern style subplot(1,3,1).