Working version till 4 processes. It doesn't work with 8 processes because of (99.99% sure) divisibility problem. The reason: domain size in Z-dimension: (1000-0)=1000, since voxel size=10 then voxels in Z-direction = 1000/10 = 100. Since there are 8 processes we have to divide 100 by 8 --> not perfectly divisible. Hence change domain size. Further the order in which the SERIAL program was generating sources and sinks was it was alternating between sources and sinks but the PARALLEL version was genearting all sources first then generating all sinks. Although random numbers generated were the same but they were alternating between sources and sinks in SERIAL version but going all to sources first then all sinks next in the PARALLEL version. Repairing this made the output the same !