Mark, this is a reasonably reduced test case. mpiexec -n 3 ./ex45 -da_grid_x 19 -da_grid_y 13 -da_grid_z 23 -pc_type gamg -pc_gamg_agg_nsmooths 1 -ksp_monitor
This is a symmetric graph, but not a symmetric matrix, though the asymmetry is only due to boundary conditions (boundary rows have only a diagonal nonzero; the other zeros are still stored explicitly). Do you have a preference about how this is handled? (I don't think we should need extra options to handle this extremely common case.) On Wed, Jan 2, 2013 at 5:27 PM, Zhenglun (Alan) Wei <zhenglun.wei at gmail.com>wrote: > Hello all, > I did some other tests. Now, it is narrow down to this situation: > The domain and grid size is: 163*81*41 with 0.0125 = dx=dy=dz. The > boundary condition is still the same. > The code runs well with 4 processes while the same problem occurs when > I was trying to use more than 4 processes (e.g. 6 or 8 processes). > > Hope this helps to detect the problem. > > thanks, > Alan > > > > -------- Original Message -------- Subject: A quick question on > 'un-symmetric graph' Date: Wed, 02 Jan 2013 15:41:47 -0600 From: Zhenglun > (Alan) Wei <zhenglun.wei at gmail.com> <zhenglun.wei at gmail.com> To: PETSc > users list <petsc-users at mcs.anl.gov> <petsc-users at mcs.anl.gov> > > Dear folks, > Here I came across a problem. > > [0]PETSC ERROR: Petsc has generated inconsistent data! > [0]PETSC ERROR: Have un-symmetric graph (apparently). Use > '-pc_gamg_sym_graph true' to symetrize the graph or '-pc_gamg_threshold > 0.0' if the matrix is structurally symmetric.! > > My code basically uses PETSc /src/ksp/ksp/example/tutorial/ex45.c > to solve the Poisson equation with the Dirichlet BC in x-direction and > the Periodic BC in y- and z- direction. > The executable file is: > > mpiexec -f $PBS_NODEFILE -np 32 ./ex45 -pc_type gamg -ksp_type cg > -pc_gamg_agg_nsmooths 1 -mg_levels_ksp_max_it 1 -mg_levels_ksp_type > richardson -ksp_rtol 1.0e-7 > > > There is no problem for my code when I use small computational > domain (83*41*21 with single core and even 163*81*41 with 4 processes). > However, when I increase the domain size (323*161*81 with 32 processes), > the error comes up. I wonder what's the possible reason of this kind of > problem. Do you need any of my output in order to do some further > inspection? or I just need to blindly add '-pc_gamg_sym_graph true' in > PETSc option? > > thanks, > Alan > > > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130105/59782800/attachment.html>
