[petsc-users] GAMG for the unsymmetrical matrix

[Barry Smith]

> Does this mean that GAMG works for the symmetrical matrix only?

  No, it means that for non symmetric nonzero structure you need the extra flag. So use the extra flag. The reason we don't always use the flag is because it adds extra cost and isn't needed if the matrix already has a symmetric nonzero structure.


  Barry

> On Apr 4, 2017, at 11:46 AM, Kong, Fande <fande.kong at inl.gov> wrote:
> 
> Hi All,
> 
> I am using GAMG to solve a group of coupled diffusion equations, but the resulting matrix is not symmetrical. I got the following error messages:
> 
> 
> [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 -1.0' if the matrix is structurally symmetric.
> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.7.5, unknown 
> [0]PETSC ERROR: /home/kongf/workhome/projects/yak/yak-opt on a arch-linux2-c-opt named r2i2n0 by kongf Mon Apr  3 16:19:59 2017
> [0]PETSC ERROR: /home/kongf/workhome/projects/yak/yak-opt on a arch-linux2-c-opt named r2i2n0 by kongf Mon Apr  3 16:19:59 2017
> [0]PETSC ERROR: #1 smoothAggs() line 462 in /home/kongf/workhome/projects/petsc/src/ksp/pc/impls/gamg/agg.c
> [0]PETSC ERROR: #2 PCGAMGCoarsen_AGG() line 998 in /home/kongf/workhome/projects/petsc/src/ksp/pc/impls/gamg/agg.c
> [0]PETSC ERROR: #3 PCSetUp_GAMG() line 571 in /home/kongf/workhome/projects/petsc/src/ksp/pc/impls/gamg/gamg.c
> [0]PETSC ERROR: #3 PCSetUp_GAMG() line 571 in /home/kongf/workhome/projects/petsc/src/ksp/pc/impls/gamg/gamg.c
> 
> Does this mean that GAMG works for the symmetrical matrix only?
> 
> Fande,