[petsc-users] Field split questions

[Colin McAuliffe]

 From what I can gather from the petsc-dev source it looks like the  
commands in 4) will then generate the splits using strided blocks. The  
problem with that is the fortran code I am using (FEAP) uses petsc to  
assemble and solve the linear problem within its own nonlinear and  
time stepping schemes. The linear problem that petsc solves already  
has boundary conditions applied to it so petsc only sees the active  
(unrestrained) equations. So then in general fields can't be extracted  
from the active equations using strided blocks and I am stuck with  
generating the index sets defining the splits on my own. Will it still  
be possible to make use of the new DM functions in this case?

FEAP website:
http://www.ce.berkeley.edu/projects/feap/

Colin


Quoting Matthew Knepley <knepley at gmail.com>:

> On Wed, Aug 8, 2012 at 10:51 PM, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Wed, Aug 8, 2012 at 10:23 PM, Colin McAuliffe   
>> <cjm2176 at columbia.edu>wrote:
>>
>>> Thanks all, regarding use of DM in 3.3, is the procedure now to create
>>> the fields with PCFieldSplitSetIS and then use DMCreateFieldDecompositionDM
>>> to create a new DM based from the new fields and the DM for the original
>>> problem?
>>>
>>
>> 1) Use petsc-dev
>>
>> 2) PCFieldSplitSetIS() is independent. This allows you to define splits
>> however you want, but then recursive gets harder
>>
>> 3) In 3.3., it uses DMCreateFieldDecompositionDM() to split all fields
>> apart at once
>>
>> 4) In petsc-dev, it uses DMCreateSubDM() which can split off any
>> combination of fields, which from the command line is something like
>>
>>      -pc_fieldsplit_0_fields 2,0 -pc_fieldsplit_1_fields 1,3
>>
>
> I should have shown recursive:
>
>   -fieldsplit_0_pc_type fieldsplit
>
> will split 2,0 into two blocks.
>
>    Matt
>
>
>>      Matt
>>
>>
>>> Colin
>>>
>>> --
>>> Colin McAuliffe
>>> PhD Candidate
>>> Columbia University
>>> Department of Civil Engineering and Engineering Mechanics
>>>
>>
>>
>>
>> --
>> 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
>>
>
>
>
> --
> 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
>



-- 
Colin McAuliffe
PhD Candidate
Columbia University
Department of Civil Engineering and Engineering Mechanics