[petsc-users] Fwd: Fieldsplit with sub pc MUMPS in parallel

[Barry Smith]

> I do not understand this behavior : since MUMPS is a parallel direct solver, shouldn't the solver converge in max 3 iterations whatever the number of procs?

   Please add  the following options

-fieldsplit_0_ksp_type gmres -fieldsplit_0_ksp_pc_side right -fieldsplit_0_ksp_monitor
-fieldsplit_1_ksp_type gmres -fieldsplit_1_ksp_pc_side right -fieldsplit_1_ksp_monitor

and send the output (don't bother with the -log_summary).

   Barry



> On Jan 4, 2017, at 3:39 PM, Karin&NiKo <niko.karin at gmail.com> wrote:
> 
> Dear Petsc team,
> 
> I am (still) trying to solve Biot's poroelasticity problem :
>  <image.png>
> 
> I am using a mixed P2-P1 finite element discretization. The matrix of the discretized system in binary format is attached to this email.
> 
> I am using the fieldsplit framework to solve the linear system. Since I am facing some troubles, I have decided to go back to simple things. Here are the options I am using :
> 
> -ksp_rtol 1.0e-5
> -ksp_type fgmres
> -pc_type fieldsplit
> -pc_fieldsplit_schur_factorization_type full
> -pc_fieldsplit_type schur
> -pc_fieldsplit_schur_precondition selfp
> -fieldsplit_0_pc_type lu
> -fieldsplit_0_pc_factor_mat_solver_package mumps
> -fieldsplit_0_ksp_type preonly
> -fieldsplit_0_ksp_converged_reason
> -fieldsplit_1_pc_type lu
> -fieldsplit_1_pc_factor_mat_solver_package mumps
> -fieldsplit_1_ksp_type preonly
> -fieldsplit_1_ksp_converged_reason
> 
> On a single proc, everything runs fine : the solver converges in 3 iterations, according to the theory (see Run-1-proc.txt [contains -log_view]).
> 
> On 2 procs, the solver converges in 28 iterations (see Run-2-proc.txt).
> 
> On 3 procs, the solver converges in 91 iterations (see Run-3-proc.txt).
> 
> I do not understand this behavior : since MUMPS is a parallel direct solver, shouldn't the solver converge in max 3 iterations whatever the number of procs?
> 
> 
> Thanks for your precious help,
> Nicolas
> 
> <Run-1-proc.txt><Run-2-proc.txt><Run-3-proc.txt><1_Warning.txt>