Thank you for the reply, Barry.
The same thing happens if I use hypre with the DMMG solver.
As you say, with hypre, the convergence is extremely slow, requiring
a lot of iterations, 1413 iterations (1820 if I use richardson) for
a 257x257
problem, while the default only needs 5.
I use the same way of handling boundary conditions in the two codes.
I've also compared the coeff matrix and rhs, and they are equal.
-Knut Erik-
Siterer Barry Smith <bsmith@xxxxxxxxxxx>:
Run with the DMMG solver with the option -pc_type hypre
What happens? Then run again with the additional option -ksp_type
richardson
Is hypre taking many, many iterations which is causing the slow
speed?
I expect there is something wrong with your code that does not use
DMMG.
Be careful how you handle boundary conditions; you need to make sure
they have the same scaling as the other equations.
Barry
On Feb 15, 2008, at 8:36 AM, knutert@xxxxxxxxxxxx wrote:
Hi Ben,
Thank you for answering. With gmres and boomeramg I get a run time
of
2s, so that is much better. However, if I increase the grid size to
513x513, I get a run time of one minute. With richardson, it
fails to converge.
LU gives 6 seconds, CG and ICC gives 7s, and the DMMG solver 3s
for the 513x513 problem.
When using the DMMG framework, I just used the default solvers.
I use the Galerkin process to generate the coarse matrices for
the multigrid cycle.
Best,
Knut
Siterer Ben Tay <zonexo@xxxxxxxxx>:
Hi Knut,
I'm currently using boomeramg to solve my poisson eqn too. I'm
using it
on my structured C-grid. I found it to be faster than LU,
especially as
the grid size increases. However I use it as a preconditioner with
GMRES as the solver. Have you tried this option? Although it's
faster,
the speed increase is usually less than double. It seems to be
worse if
there is a lot of stretching in the grid.
Btw, your mention using the DMMG framework and it takes less than a
sec. What solver or preconditioner did you use? It's 4 times faster
than GMRES...
thanks!
knutert@xxxxxxxxxxxx wrote:
Hello,
I am trying to use the hypre multigrid solver to solve a Poisson
equation.
However, on a test case with grid size 257x257 it takes 40
seconds to converge
on one processor when I run with
./run -ksp_type richardson -pc_type hypre -pc_type_hypre boomeramg
Using the DMMG framework, the same problem takes less than a
second,
and the default gmres solver uses only four seconds.
Am I somehow using the solver the wrong way, or is this
performance expected?
Regards
Knut Erik Teigen