[petsc-users] subprocess (block) tolerance.

[Smith, Barry F.]

> On Oct 4, 2018, at 6:09 PM, HeeHo Park <heeho.park at gmail.com> wrote:
> 
> 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]? 

   You can say it that way. 
> 
> 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