[petsc-users] DMPlex with spring elements

[Matthew Knepley]

On Fri, Sep 26, 2014 at 10:06 AM, Miguel Angel Salazar de Troya <
salazardetroya at gmail.com> wrote:

> That means that if we call SNESSetFunction() we don't build the residual
> vector in parallel? In the pflow example (
> http://www.mcs.anl.gov/petsc/petsc-as/petsc-current/src/snes/examples/tutorials/network/pflow/pf.c.html)
> the function FormFunction() (Input for SNESSetFunction() works with the
> local vectors. I don't understand this.
>

FormFunction() in that link clearly takes in a global vector X and returns
a global vector F. Inside, it
converts them to local vectors. This is exactly what you would do for a
function given to SNESSetFunction().

  Matt


>
> Thanks
> Miguel
>
> On Fri, Sep 26, 2014 at 9:34 AM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> On Fri, Sep 26, 2014 at 9:31 AM, Miguel Angel Salazar de Troya <
>> salazardetroya at gmail.com> wrote:
>>
>>> Thanks. I had another question about the DM and SNES and TS. There are
>>> similar routines to assign the residual and jacobian evaluation to both
>>> objects. For the SNES case are:
>>>
>>> DMSNESSetFunctionLocal
>>> DMSNESSetJacobianLocal
>>>
>>> What are the differences of these with:
>>>
>>> SNESSetFunction
>>> SNESSetJacobian
>>>
>>
>> SNESSetFunction() expects the user to construct the entire parallel
>> residual vector. DMSNESSetFunctionLocal()
>> expects the user to construct the local pieces of the residual, and then
>> it automatically calls DMLocalToGlobal()
>> to assembly the full residual. It also converts the input from global
>> vectors to local vectors, and in the case of
>> DMDA multidimensional arrays.
>>
>>   Thanks,
>>
>>     Matt
>>
>>
>>> and when should we use each? With "Local", it is meant to evaluate the
>>> function/jacobian for the elements in the local processor? I could get the
>>> local edges in DMNetwork by calling DMNetworkGetEdgeRange?
>>>
>>> Miguel
>>>
>>> On Thu, Sep 25, 2014 at 5:17 PM, Matthew Knepley <knepley at gmail.com>
>>> wrote:
>>>
>>>> On Thu, Sep 25, 2014 at 5:15 PM, Miguel Angel Salazar de Troya <
>>>> salazardetroya at gmail.com> wrote:
>>>>
>>>>> > If you need a symmetric Jacobian, you can use the BC facility in
>>>>> > PetscSection, which eliminates the
>>>>> > variables completely. This is how the FEM examples, like ex12, work.
>>>>>
>>>>> Would that be with PetscSectionSetConstraintDof ? For that I will need
>>>>> the PetscSection, DofSection, within DMNetwork, how can I obtain it? I
>>>>> could cast it to DM_Network from the dm, networkdm,  declared in the main
>>>>> program, maybe something like this:
>>>>>
>>>>> DM_Network     *network = (DM_Network*) networkdm->data;
>>>>>
>>>>> Then I would loop over the vertices and call PetscSectionSetConstraintDof if it's a boundary node (by checking the corresponding component)
>>>>>
>>>>> I admit to not completely understanding DMNetwork. However, it
>>>> eventually builds a PetscSection for data layout, which
>>>> you could get from DMGetDefaultSection(). The right thing to do is find
>>>> where it builds the Section, and put in your BC
>>>> there, but that sounds like it would entail coding.
>>>>
>>>>   Thanks,
>>>>
>>>>      Matt
>>>>
>>>>
>>>>> Thanks for your responses.
>>>>>
>>>>> Miguel
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Sep 25, 2014 at 2:42 PM, Jed Brown <jed at jedbrown.org> wrote:
>>>>>
>>>>>> Matthew Knepley <knepley at gmail.com> writes:
>>>>>>
>>>>>> > On Thu, Sep 25, 2014 at 1:46 PM, Abhyankar, Shrirang G. <
>>>>>> abhyshr at mcs.anl.gov
>>>>>> >> wrote:
>>>>>> >
>>>>>> >> You are right. The Jacobian for the power grid application is
>>>>>> indeed
>>>>>> >> non-symmetric. Is that a problem for your application?
>>>>>> >>
>>>>>> >
>>>>>> > If you need a symmetric Jacobian, you can use the BC facility in
>>>>>> > PetscSection, which eliminates the
>>>>>> > variables completely. This is how the FEM examples, like ex12, work.
>>>>>>
>>>>>> You can also use MatZeroRowsColumns() or do the equivalent
>>>>>> transformation during assembly (my preference).
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> *Miguel Angel Salazar de Troya*
>>>>> Graduate Research Assistant
>>>>> Department of Mechanical Science and Engineering
>>>>> University of Illinois at Urbana-Champaign
>>>>> (217) 550-2360
>>>>> salaza11 at illinois.edu
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>>>
>>>
>>>
>>>
>>> --
>>> *Miguel Angel Salazar de Troya*
>>> Graduate Research Assistant
>>> Department of Mechanical Science and Engineering
>>> University of Illinois at Urbana-Champaign
>>> (217) 550-2360
>>> salaza11 at illinois.edu
>>>
>>>
>>
>>
>> --
>> 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
>>
>
>
>
> --
> *Miguel Angel Salazar de Troya*
> Graduate Research Assistant
> Department of Mechanical Science and Engineering
> University of Illinois at Urbana-Champaign
> (217) 550-2360
> salaza11 at illinois.edu
>
>


-- 
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/20140926/8944b974/attachment.html>