[petsc-users] Multiple points constraint in parallel

[YuSh Lo]

Matthew Knepley <knepley at gmail.com> 於 2023年5月31日 週三 下午1:02寫道：

> 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 first create a serial DM and use DMLabel to mark those nodes, and
store them in IS. Then I call DMPlexDistribute.


>
>
>>
>>>
>>>> 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/>
>
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