[petsc-users] Field split questions

[Matthew Knepley]

On Thu, Aug 9, 2012 at 7:41 AM, Colin McAuliffe <cjm2176 at columbia.edu>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


No. I never use strided blocks.

   Matt


> 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/<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
>



-- 
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
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