[petsc-users] AMG for block matrices

[Matthew Knepley]

On Wed, Sep 23, 2020 at 9:26 AM Mark Adams <mfadams at lbl.gov> wrote:

> Generally you do want to use FieldSplit but Vanka might work.
>

Just to be clear, these suggestions apply to _incompressible_ Navier-Stokes.

  Thanks,

     Matt


> I'm not sure what to use as the smoother KSP. -mg_levels_ksp_type [gmres |
> richardson]. If you use richardson you will probably want to fiddle with
> the damping.
>
>
>
> On Tue, Sep 22, 2020 at 11:23 PM Barry Smith <bsmith at petsc.dev> wrote:
>
>>
>>   Raju,
>>
>>     If you call MatSetBlockSize(mat,4) then GAMG will keep the 4
>> variables together through all the levels.
>>
>>     You might consider using the point block Jacobi smoother with it
>> instead of the default Jacobi smoother -mg_levels_pc_type pbjacobi
>>
>>     There is also PCPATCH which supports Vanka smoothing (though it is to
>> well hidden) PCPatchSetConstructType(pc,PC_PATCH_VANKA)
>> -pc_patch_construct_type vanka
>>
>>
>>     For coupled Navier stokes you might also consider using PCFIELDSPLIT
>> and GAMG just for the pressure solve inside it.
>>
>>   Barry
>>
>> > On Sep 22, 2020, at 9:24 PM, Raju Mandhapati via petsc-users <
>> petsc-users at mcs.anl.gov> wrote:
>> >
>> > Hello,
>> >
>> > Does Petsc have an option to solve block matrices using AMG
>> solver/preconditioner. My block matrix is coming from solving u,v,w,p
>> (coupled Navier stokes) at each cell.
>> >
>> > thanks
>> > Raju.
>>
>>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200923/5c0b4d09/attachment-0001.html>