[Beowulf] Parallel Programming Question

[amjad ali]

Hello All,

On my 4-node Beowulf Cluster, when I run my PDE solver code (compiled
with mpif90 of openmpi-installed-with-gfortran) with -np 4 launched
only on the Head Node (without providing -machinefile), it gives me
correct results. ONLY one problem is there: when I monitor RAM
behavior it gets filling at a constant speed throughout the RUN of
program, till I get final result. So Why the usage of RAM is
constantly increasing (although this is not the case with relevant
serial code of the same problem/algorithm/method).

Secondly when I launch the same compiled code on 4 nodes (with
-machinefile option). Then I do not get correct result. The
convergence gets very much slow down after few iterations, ultimately
resulting in NaN values of problem variables.

I would be very grateful for having comments for the remedy of above
two difficulties/confusions.

with best regards,
Amjad Ali.