[petsc-users] Field split questions

[Matthew Knepley]

On Thu, Aug 9, 2012 at 9:21 AM, Sanjay Govindjee <s_g at berkeley.edu> wrote:

> 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).
>

However, this is not necessary with the DM interface.

   Matt


> -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/<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
>
> 779 Davis Hall
> Structural Engineering, Mechanics and Materials
> Department of Civil Engineering
> University of California
> Berkeley, CA 94720-1710
>
> Voice:  +1 510 642 6060
> FAX:    +1 510 643 5264
> s_g at berkeley.edu
> http://www.ce.berkeley.edu/~**sanjay <http://www.ce.berkeley.edu/~sanjay>
> ------------------------------**-----------------
>
>


-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120809/ded434c2/attachment.html>