[petsc-users] DMPlex problem

Mon Sep 26 09:04:56 CDT 2016

On Mon, Sep 26, 2016 at 8:41 AM, Morten Nobel-Jørgensen <mono at dtu.dk> wrote:

> Hi Matt
>
> We are trying to do a simple FE using DMPlex, but when assemble the global
> stiffness matrix we get in problems when running NP>1 - that is the global
> matrix differs when we move to a distributed system, where it should not.
>
> In pseudo-code our CreateGlobalStiffnessMatrix does the following
>
> create a local stiffness matrix ke with some values
> for each local cell/element e (using result from
> DMPlexGetHeightStratum(..,0,..)
>     for each of its vertices (using DMPlexGetTransitiveClosure(..,e,..)
>         set local/global mapping to edof
> update the global stiffness matrix K using the local mapping edof and
> values ke
>
>
> The code we have sent is a simplified version, which just builds a dummy
> stiffness matrix - but we believe this matrix should still the same
> independent of NP. (That is why we use trace).
>

I am not sure what is wrong there, but there are a bunch of Plex FEM
examples, like SNES ex12, ex62, ex77.

> I'm not familiar with MatSetValuesClosure(). Is that the missing piece?
>

I use this to do indexing since it is so error prone to do it by yourself.
I think this could be the problem with your example.

When you distribute the mesh, ordering changes, and we do permutations to
keep all local indices contiguous. The
MatSetValuesClosure() is a convenience function for FEM which takes in a
mesh point (could be cell, face, etc.) and
translates that point number to a set of row indices using

  a) the transitive closure of that point in the mesh DAG

and

  b) the default PetscSection for the DM which maps mesh points to sets of
dofs (row indices)

For it to work, you need to setup the default DM section, which it looks
like you have done.

  Thanks,

    Matt

> Kind regards,
> Morten
>
>
> ------------------------------
> *From:* Matthew Knepley [knepley at gmail.com]
> *Sent:* Monday, September 26, 2016 2:19 PM
> *To:* Morten Nobel-Jørgensen
> *Cc:* PETSc ‎[petsc-users at mcs.anl.gov]‎
> *Subject:* Re: [petsc-users] DMPlex problem
>
> On Mon, Sep 26, 2016 at 7:00 AM, Morten Nobel-Jørgensen <mono at dtu.dk>
> wrote:
>
>> Hi Matthew
>>
>> It seems like the problem is not fully fixed. I have changed the code to
>> now run on with both 2,3 and 4 cells. When I run the code using NP = 1..3 I
>> get different result both for NP=1 to NP=2/3 when cell count is larger than
>> 2.
>>
>
> Do you mean the trace? I have no idea what you are actually putting in.
>
> I have a lot of debugging when you use, MatSetValuesClosure(), but when
> you directly use
> MatSetValuesLocal(), you are handling things yourself.
>
>   Thanks,
>
>      Matt
>
>
>> Kind regards,
>> Morten
>> ____
>> mpiexec -np 1 ./ex18k
>> cells 2
>> Loc size: 36
>> Trace of matrix: 132.000000
>> cells 3
>> Loc size: 48
>> Trace of matrix: 192.000000
>> cells 4
>> Loc size: 60
>> Trace of matrix: 258.000000
>> mpiexec -np 2 ./ex18k
>> cells 2
>> Loc size: 24
>> Loc size: 24
>> Trace of matrix: 132.000000
>> cells 3
>> Loc size: 36
>> Loc size: 24
>> Trace of matrix: 198.000000
>> cells 4
>> Loc size: 36
>> Loc size: 36
>> Trace of matrix: 264.000000
>> mpiexec -np 3 ./ex18k
>> cells 2
>> Loc size: 24
>> Loc size: 24
>> Loc size: 0
>> Trace of matrix: 132.000000
>> cells 3
>> Loc size: 24
>> Loc size: 24
>> Loc size: 24
>> Trace of matrix: 198.000000
>> cells 4
>> Loc size: 36
>> Loc size: 24
>> Loc size: 24
>> Trace of matrix: 264.000000
>>
>>
>>
>>
>> ------------------------------
>> *From:* petsc-users-bounces at mcs.anl.gov [petsc-users-bounces at mcs.anl.gov]
>> on behalf of Morten Nobel-Jørgensen [mono at dtu.dk]
>> *Sent:* Sunday, September 25, 2016 11:15 AM
>> *To:* Matthew Knepley
>> *Cc:* PETSc ‎[petsc-users at mcs.anl.gov]‎
>> *Subject:* Re: [petsc-users] DMPlex problem
>>
>> Hi Matthew
>>
>> Thank you for the bug-fix :) I can confirm that it works :)
>>
>> And thanks for your hard work on PETSc - your work is very much
>> appreciated!
>>
>> Kind regards,
>> Morten
>> ------------------------------
>> *From:* Matthew Knepley [knepley at gmail.com]
>> *Sent:* Friday, September 23, 2016 2:46 PM
>> *To:* Morten Nobel-Jørgensen
>> *Cc:* PETSc ‎[petsc-users at mcs.anl.gov]‎
>> *Subject:* Re: [petsc-users] DMPlex problem
>>
>> On Fri, Sep 23, 2016 at 7:45 AM, Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Fri, Sep 23, 2016 at 3:48 AM, Morten Nobel-Jørgensen <mono at dtu.dk>
>>> wrote:
>>>
>>>> Dear PETSc developers
>>>>
>>>> Any update on this issue regarding DMPlex? Or is there any obvious
>>>> workaround that we are unaware of?
>>>>
>>>
>>> I have fixed this bug. It did not come up in nightly tests because we
>>> are not using MatSetValuesLocal(). Instead we
>>> use MatSetValuesClosure() which translates differently.
>>>
>>> Here is the branch
>>>
>>>   https://bitbucket.org/petsc/petsc/branch/knepley/fix-dm-ltog-bs
>>>
>>> and I have merged it to next. It will go to master in a day or two.
>>>
>>
>> Also, here is the cleaned up source with no memory leaks.
>>
>>   Matt
>>
>>
>>> Also should we additionally register the issue on Bitbucket or is
>>>> reporting the issue on the mailing list enough?
>>>>
>>>
>>> Normally we are faster, but the start of the semester was hard this year.
>>>
>>>   Thanks,
>>>
>>>      Matt
>>>
>>>
>>>> Kind regards,
>>>> Morten
>>>>
>>>> ------------------------------
>>>> *From:* Matthew Knepley [knepley at gmail.com]
>>>> *Sent:* Friday, September 09, 2016 12:21 PM
>>>> *To:* Morten Nobel-Jørgensen
>>>> *Cc:* PETSc ‎[petsc-users at mcs.anl.gov]‎
>>>> *Subject:* Re: [petsc-users] DMPlex problem
>>>>
>>>> On Fri, Sep 9, 2016 at 4:04 AM, Morten Nobel-Jørgensen <mono at dtu.dk>
>>>> wrote:
>>>>
>>>>> Dear PETSc developers and users,
>>>>>
>>>>> Last week we posted a question regarding an error with DMPlex and
>>>>> multiple dofs and have not gotten any feedback yet. This is uncharted
>>>>> waters for us, since we have gotten used to an extremely fast feedback from
>>>>> the PETSc crew. So - with the chance of sounding impatient and ungrateful -
>>>>> we would like to hear if anybody has any ideas that could point us in the
>>>>> right direction?
>>>>>
>>>>
>>>> This is my fault. You have not gotten a response because everyone else
>>>> was waiting for me, and I have been
>>>> slow because I just moved houses at the same time as term started here.
>>>> Sorry about that.
>>>>
>>>> The example ran for me and I saw your problem. The local-tp-global map
>>>> is missing for some reason.
>>>> I am tracking it down now. It should be made by DMCreateMatrix(), so
>>>> this is mysterious. I hope to have
>>>> this fixed by early next week.
>>>>
>>>>   Thanks,
>>>>
>>>>     Matt
>>>>
>>>>
>>>>> We have created a small example problem that demonstrates the error in
>>>>> the matrix assembly.
>>>>>
>>>>> Thanks,
>>>>> Morten
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>>
>>
>>
>>
>> --
>> 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
>

-- 
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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