[petsc-users] Fwd: A quick question on 'un-symmetric graph'

[Zhenglun (Alan) Wei]

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>
To: 	PETSc users list <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



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