How to use palabos to solve poisson equation in parallel

Hi everyone,
I’m trying to solve poisson equation with complex geometric boundary condition in palabos with SOR method. I need to compare the value of each node in the scalar field before and after each iteration step, and get the difference. Then, I’ll get the biggest difference among all the nodes, and compare it with the tolerance I set. If it is larger than the tolerance, the iteration will go on. The problem is when I try to parallelize the system, how can I get the difference from each computational domain, and then compare the the differences and return the biggest one to each domain?