[petsc-users] gamg and zero pivots

[Barry Smith]

> On Sep 18, 2015, at 10:42 PM, Gideon Simpson <gideon.simpson at gmail.com> wrote:
> 
> I’m getting a zero pivot in LU factorization error when I use the gamg preconditioner.  I know there is some issue with my matrix, as I get the same error if I use pc_type lu in serial, or if I use pc_type bjacobi in parallel, both of which are corrected by adding -pc_factor_shift_type NONZERO -sub_pc_factor_shift_type NONZERO, respectively.  However, I can’t quite seem to figure out the analogous command to use for the gamg preconditioner.

  You need to figure out the prefix to the option that is added by gamg to set it. One way is to run with the gamg options and -help and grep for factor_shift.   

   The option is like something like -mg_coarse_pc_factor_shift_type nonzero or -mg_coarse_sub_pc_factor_shift_type 

  Barry

> 
> -gideon
>