A 3D example of KSPSolve?

[Shi Jin]

Hi there,

I am tuning our 3D FEM CFD code written with PETSc.
The code doesn't scale very well. For example, with 8
processes on a linux cluster, the speedup we achieve
with a fairly large problem size(million of elements)
is only 3 to 4 using the Congugate gradient solver. We
can achieve a speed up of a 6.5 using a GMRes solver
but the wall clock time of a GMRes is longer than a CG
solver which indicates that CG is the faster solver
and it scales not as good as GMRes. Is this generally
true?

I then went to the examples and find a 2D example of
KSPSolve (ex2.c). I let the code ran with a 1000x1000
mesh and get a linear scaling of the CG solver and a
super linear scaling of the GMRes. These are both much
better than our code. However, I think the 2D nature
of the sample problem might help the scaling of the
code. So I would like to try some 3D example using the
KSPSolve. Unfortunately, I couldn't find such an
example either in the src/ksp/ksp/examples/tutorials
directory or by google search. There are a couple of
3D examples in the src/ksp/ksp/examples/tutorials but
they   are about the SNES not KSPSolve. If anyone can
provide me with such an example, I would really
appreciate it.
Thanks a lot.

Shi


 
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