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 at mcs.anl.gov>: > > 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 at stud.ntnu.no 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 at gmail.com>: >> >>> 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 at stud.ntnu.no 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 >>>> >>>> >> >> >>
