Solving Poisson type of equation, increasing tolerance requirement leads to no response

I am solving a poisson type of equation, and when I increase the tolerance requirement down to 10e-7, the command window stops refreshing and the system shows busy, and gives no response. Any ideas on how to solve that problem?

Answer 1

[elias GR]

The solution does not converge. It does not converge even with the 10-5 tolerance. You should print the max variable at each step to see that. You should check your code for mistakes. If you need more help you need to provide more info about the problem you try to solve (what is the equation, what is the numerical method etc).