Solving 2 eqns at the same time in PETSc

[Ben Tay]

Hi,

(I sent this email a while ago but I use a different email address. Not 
sure if it got through since it's not registered in the server list. 
Sorry if it was resent.)

I obtain 2 linear eqns (u and v velocity) from the momentum eqn in my 
CFD code. Instead of solving eqn 1 in parallel, and then subsequently 
eqn 2 in parallel, I am thinking of solving the 2 eqns at the same time, 
using half the number of processors on each eqn. In other words, when 
using 4 processors, I use 2 processors for eqn 1 and 2 processors for 
eqn 2. Will that be possible?

I thought that in MPI, if an equation is divided among too many 
processors, its scaling factor will decrease. So by dividing into less 
processors and solving them simultaneously, it will give better 
performance. Is that true?

I've also successfully coded 1 eqn to be solved in parallel in PETSc. 
What changes do I have to made now?

Thank you very much.

Regards.