[petsc-users] Field split questions

[Sanjay Govindjee]

Colin,
   I you block the equations in FEAP, then the restrained BCs are 
'included' in assembled PETSc matrix (these dofs have rows that are zero 
modulo a value of unity on the diagonal and the restrained value on the 
right-hand side).

-sg

On 8/9/12 8:41 AM, Colin McAuliffe wrote:
> 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
>>
>
>
>

-- 
-----------------------------------------------
Sanjay Govindjee, PhD, PE
Professor of Civil Engineering
Vice Chair for Academic Affairs

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