[petsc-users] subprocess (block) tolerance.

[HeeHo Park]

Barry and Jed,

Thank you for your answers. I think I need to learn more about domain
decomposition as I am a bit confused.
Is it true that we are using BiCGstab here to solve the system of
equations, using Additive Schwartz as a domain decomposition
preconditioner, and that precondition matrix for each block is
preconditioned by ilu[0]?

Thanks,


On Thu, Oct 4, 2018 at 5:53 PM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>   Since
>
> KSP Object: (flow_sub_) 1 MPI processes
>         type: preonly
>
> this means only a single iteration of the inner solver is used so   the
> numbers in red are not used.
>
> You could do something like -flow_ksp_type fgmres -flow_sub_ksp_type gmres
> -flow_sub_ksp_rtol 1.e-2 but it wouldn't help maters. Likely the current
> values are the best.
>
>    Barry
>
>
> > On Oct 4, 2018, at 5:44 PM, HeeHo Park <heeho.park at gmail.com> wrote:
> >
> > Hi, I'm running PFLOTRAN and in PFLOTRAN, we have flow_ and flow_sub_
> processes. I was wondering what the red underlined values meant (each block
> tolerance?) and how to change them (would it affect convergence?). Blue
> marked bold values are changed from the default values for linear solvers.
> >
> > FLOW Linear Solver
> >                        solver: bcgs
> >                preconditioner: asm
> >                          atol: 1.000000E-10
> >                          rtol: 1.000000E-10
> >                          dtol: 1.000000E+04
> >             maximum iteration: 10000
> > KSP Object: (flow_) 8 MPI processes
> >   type: bcgs
> >   maximum iterations=10000, initial guess is zero
> >   tolerances:  relative=1e-10, absolute=1e-10, divergence=10000.
> >   left preconditioning
> >   using PRECONDITIONED norm type for convergence test
> > PC Object: (flow_) 8 MPI processes
> >   type: asm
> >     Additive Schwarz: total subdomain blocks = 8, amount of overlap = 1
> >     Additive Schwarz: restriction/interpolation type - RESTRICT
> >     [0] number of local blocks = 1
> >     [1] number of local blocks = 1
> >     [2] number of local blocks = 1
> >     [3] number of local blocks = 1
> >     [4] number of local blocks = 1
> >     [5] number of local blocks = 1
> >     [6] number of local blocks = 1
> >     [7] number of local blocks = 1
> >     Local solve info for each block is in the following KSP and PC
> objects:
> >     - - - - - - - - - - - - - - - - - -
> >     [0] local block number 0, size = 1389
> >     KSP Object: (flow_sub_) 1 MPI processes
> >       type: preonly
> >       maximum iterations=10000, initial guess is zero
> > >>>      tolerances:  relative=1e-05, absolute=1e-50, divergence=10000.
> >       left preconditioning
> >       using DEFAULT norm type for convergence test
> >     PC Object: (flow_sub_) 1 MPI processes
> >       type: ilu
> >       PC has not been set up so information may be incomplete
> >         out-of-place factorization
> >         0 levels of fill
> >         tolerance for zero pivot 2.22045e-14
> >         using diagonal shift on blocks to prevent zero pivot [INBLOCKS]
> >         matrix ordering: natural
> >       linear system matrix = precond matrix:
> >       Mat Object: (flow_) 1 MPI processes
> >         type: seqbaij
> >         rows=1389, cols=1389, bs=3
> >         total: nonzeros=20025, allocated nonzeros=20025
> >         total number of mallocs used during MatSetValues calls =0
> >             block size is 3
> >     - - - - - - - - - - - - - - - - - -
> >
> > --
> > HeeHo Daniel Park
>
>

-- 
HeeHo Daniel Park
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