Solve a system with two processors

[Isabel Gil <misabel@xxxxxxxxxxxxx>]

Hello PETSc's users!

I have a problem with my parallel program.
If I run it with only one processor (mpirun -np 1...), everything is all 
right but if I use 2 processors (mpi -np 2...), the problem appears.

When I want to solve my matricial system through a solver, after having 
created my matrices without any hitch, I have the following problem:

The two processes that are running in two different processors using 
100% of CPU and 14.6% of memory each of them, end up using 0% of CPU and 
14.6% of memory and, although the program doesn't break down, both of 
the processes don't do anything. This looks like a lockup: one processor 
is waiting for a message from the second one, but the second one thinks 
that it doesn't have to send anything and is instead waiting for 
something else from the first processor.

But I don't know how to avoid this problem since it is supposed that I 
don't have to use "MPI_Send()" and "MPI_Recv()" functions because PETSc 
itself deals with it, do I?.
Any advice will be welcome.

Thanks in advance and best regards
Isa