[petsc-users] Multiple points constraint in parallel

[Matthew Knepley]

On Wed, May 31, 2023 at 1:53 PM YuSh Lo <ysjosh.lo at gmail.com> wrote:

> Hi Matthew,
>
> Matthew Knepley <knepley at gmail.com> 於 2023年5月31日 週三 上午5:08寫道：
>
>> On Wed, May 31, 2023 at 1:25 AM YuSh Lo <ysjosh.lo at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I have some multiple points constraint input as follows,
>>>
>>> A_1 a_4
>>> B_2 b_5
>>> C_3 c_6
>>>
>>> each columns are stored in different IS.
>>>
>>
>> So one IS lists the capital letter and one lists the lowercase?
>>
>        Yes.
>
>>
>>
>>> After dmplex distribute, they will be renumbered and distribution to
>>> certain processors.
>>>
>>
>> Plex does normally renumber and send ISes, so you are doing this yourself?
>>
>      No, Plex does the distribution.
>

I do not understand this. How does the DM know about this IS? Are you
calling DMDistributeFieldIS()?


>
>>
>>> I have two questions:
>>>
>>> (1) I need both complete ISs are all the processors. Can I just do
>>> ISALLGather()?
>>>
>>
>> I think so. I cannot tell what you want to do.
>>
>>
>>> (2) Although renumbered, will the original order remain(ABC and abc)?
>>> If the number is the node number, after distribution and I do an
>>> ISALLGather()
>>> will I have the following on each processor?
>>>
>>> A_3 a_1
>>> B_4 b_2
>>> C_6 c_5
>>> (I randomly renumber them)
>>>
>>>
>>> This is what I can come up with now. Is there any better way to do it?
>>>
>>
>> Can you tell me what you want to use this for? Maybe there is an easier
>> way. For example,
>> if we want to impose a constraint on a mesh point, usually I mark that
>> point with a DMLabel.
>> These are propagated during distribution so you do not have to think
>> about it.
>>
>
>     So I have to impose constraint between two nodes. The upper case node
> is controlled by the lower case node, and there can be many pairs of
> constraint. When looping over elements if one node is controlled by the
> other then the corresponding entry has to be added to a different location
> e.x. [an index][A_3] to [an index][a_1]. I know how to use DMLabel, but I
> have used it on one node at a time only. I used DMLabel to mark those nodes
> with BCs. Now I must know the info of two nodes at the same time. The
> operations only have to done in assembling and calculating the element
> stiffness matrix of the elements that contain the upper case node, but I
> must know the info of the corresponding lower case node so I know where to
> assemble the entry.
>

Oh, if you want to associate two mesh points, use a PetscSF. These can also
be remapped.

  Thanks,

    Matt


> Thanks,
> Josh
>
>
>>
>>   Thanks,
>>
>>      Matt
>>
>>
>>> Thanks,
>>> Josh
>>>
>>
>>
>> --
>> 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
>>
>> https://www.cse.buffalo.edu/~knepley/
>> <http://www.cse.buffalo.edu/~knepley/>
>>
>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20230531/aa8106b1/attachment.html>