[petsc-users] Vec Ownership ranges with Global Section Offsets
Matthew Knepley
knepley at gmail.com
Fri Jan 6 09:04:39 CST 2023
On Fri, Jan 6, 2023 at 9:56 AM Nicholas Arnold-Medabalimi <
narnoldm at umich.edu> wrote:
> Apologies. If it helps, there is one cell of overlap in this small test
> case for a 2D mesh that is 1 cell in height and a number of cells in
> length. .
>
> process 0
> Petsc VecGetLocalSize 2750
> size(stateVecV) 2750
>
> process 1
> Petsc VecGetLocalSize 2640
> size(stateVecV) 2640
>
The offsets shown below are well-within these sizes. I do not understand
the problem.
Thanks,
Matt
> On Fri, Jan 6, 2023 at 9:51 AM Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Fri, Jan 6, 2023 at 9:37 AM Nicholas Arnold-Medabalimi <
>> narnoldm at umich.edu> wrote:
>>
>>> Hi Matt
>>>
>>> I made a typo on the line statVecV(offset) = <set to something> in my
>>> example, I agree. (I wrote that offhand since the actual assignment is much
>>> larger) I should be statVecV(offset+1) = <assignment> so I'm confident it's
>>> not a 1 0 indexing thing.
>>>
>>> My question is more related to what is happening in the offsets. c0 and
>>> c1 are pulled using DMplexgetheight stratum, so they are zero-indexed
>>> (which is why I loop from c0 to (c1-1)).
>>>
>>> For the size inquiries. on processor 0
>>> Petsc VecGetSize(stateVec) 5390
>>>
>>
>> I need to see VecGetLocalSize()
>>
>> Matt
>>
>>
>>> size(stateVecV) 2640
>>>
>>> on processor 1
>>> Petsc VecGetSize 5390
>>> size(stateVecV) 2750
>>>
>>> It's quite weird to me that processor one can have a positive offset
>>> that is less than its starting ownership index (in the initial email
>>> output).
>>>
>>> Thanks for the assistance
>>> Nicholas
>>>
>>>
>>> On Fri, Jan 6, 2023 at 9:20 AM Matthew Knepley <knepley at gmail.com>
>>> wrote:
>>>
>>>> On Fri, Jan 6, 2023 at 2:28 AM Nicholas Arnold-Medabalimi <
>>>> narnoldm at umich.edu> wrote:
>>>>
>>>>> Hi Petsc Users,
>>>>>
>>>>> I'm working with a dmplex system with a subsampled mesh distributed
>>>>> with an overlap of 1.
>>>>>
>>>>> I'm encountering unusual situations when using VecGetOwnershipRange to
>>>>> adjust the offset received from a global section. The logic of the
>>>>> following code is first to get the offset needed to index a global vector
>>>>> while still being able to check if it is an overlapped cell and skip if
>>>>> needed while counting the owned cells.
>>>>>
>>>>
>>>>
>>>>>
>>>>> call DMGetGlobalSection(dmplex,section,ierr)
>>>>> call VecGetArrayF90(stateVec,stateVecV,ierr)
>>>>> call VecGetOwnershipRange(stateVec,oStart,oEnd,ierr)
>>>>> do i = c0, (c1-1)
>>>>>
>>>>> call PetscSectionGetOffset(section,i,offset,ierr)
>>>>> write(*,*) "cell",i,"offset",offset,'oStart',oStart, offset-oStart
>>>>>
>>>>> if(offset<0) then
>>>>> cycle
>>>>> endif
>>>>> offset=offset-oStart
>>>>> plexcells=plexcells+1
>>>>> stateVecV(offset)= <set to something> enddo
>>>>>
>>>>> I'm noticing some very weird results that I've appended below. The
>>>>> GetOffset documentation notes that a negative offset indicates an unowned
>>>>> point (which I use to cycle). However, the offset subtraction with oStart
>>>>> will yield an illegal index for the Vector access. I see that on the
>>>>> documentation for GetOwnershipRange, it notes that this may be
>>>>> "ill-defined" but I wanted to see if this is type of ill-defined I can
>>>>> expect or there is just something terribly wrong with my PetscSection.(both
>>>>> the Vec and Section were produced from DMPlexDistributeField so should by
>>>>> definition have synchronized section information) I was wondering if there
>>>>> is a possible output and/or the best way to index the vector. I'm thinking
>>>>> of subtracting the offset of cell 0 perhaps?
>>>>>
>>>>
>>>> Can you show your vector sizes? Are you sure it is not the fact that
>>>> F90 arrays use 1-based indices, but these are 0-based offsets?
>>>>
>>>> Thanks,
>>>>
>>>> Matt
>>>>
>>>>
>>>>> on rank 0
>>>>>
>>>>> cell 0 offset 0 oStart 0 0
>>>>> cell 1 offset 55 oStart 0 55
>>>>> cell 2 offset 110 oStart 0 110
>>>>> cell 3 offset 165 oStart 0 165
>>>>> cell 4 offset 220 oStart 0 220
>>>>> cell 5 offset 275 oStart 0 275
>>>>> cell 6 offset 330 oStart 0 330
>>>>> cell 7 offset 385 oStart 0 385
>>>>> cell 8 offset 440 oStart 0 440
>>>>> cell 9 offset 495 oStart 0 495
>>>>> cell 10 offset 550 oStart 0 550
>>>>> cell 11 offset 605 oStart 0 605
>>>>> cell 12 offset 660 oStart 0 660
>>>>> cell 13 offset 715 oStart 0 715
>>>>>
>>>>> and on rank one
>>>>> cell 0 offset 2475 oStart 2640 -165
>>>>> cell 1 offset 2530 oStart 2640 -110
>>>>> cell 2 offset 2585 oStart 2640 -55
>>>>> cell 3 offset 2640 oStart 2640 0
>>>>> cell 4 offset 2695 oStart 2640 55
>>>>> cell 5 offset 2750 oStart 2640 110
>>>>> cell 6 offset 2805 oStart 2640 165
>>>>> cell 7 offset 2860 oStart 2640 220
>>>>> cell 8 offset 2915 oStart 2640 275
>>>>> cell 9 offset 2970 oStart 2640 330
>>>>> cell 10 offset 3025 oStart 2640 385
>>>>> cell 11 offset 3080 oStart 2640 440
>>>>> cell 12 offset 3135 oStart 2640 495
>>>>> cell 13 offset 3190 oStart 2640 550
>>>>> cell 14 offset 3245 oStart 2640 605
>>>>> cell 15 offset -771 oStart 2640 -3411
>>>>>
>>>>>
>>>>> Sincerely
>>>>> Nicholas
>>>>>
>>>>> --
>>>>> Nicholas Arnold-Medabalimi
>>>>>
>>>>> Ph.D. Candidate
>>>>> Computational Aeroscience Lab
>>>>> University of Michigan
>>>>>
>>>>
>>>>
>>>> --
>>>> 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/>
>>>>
>>>
>>>
>>> --
>>> Nicholas Arnold-Medabalimi
>>>
>>> Ph.D. Candidate
>>> Computational Aeroscience Lab
>>> University of Michigan
>>>
>>
>>
>> --
>> 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/>
>>
>
>
> --
> Nicholas Arnold-Medabalimi
>
> Ph.D. Candidate
> Computational Aeroscience Lab
> University of Michigan
>
--
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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