thank you Peter for your response, i undertand what you explain and i will try what you suggest. i have also notice one other thing that seems to me very weird. the computaion takes less time when usingĀ  a lower number of core than a higer. for exemple that takes 12h for a 16 cores and 6h40 for a 2 cores. i had try to understand why a i have this and finally i think that when the process is dirtriuted, the sum of memories requested by each core will be higher than when we have less core. is that corect for you?