[petsc-users] Vec Ownership ranges with Global Section Offsets
Matthew Knepley
knepley at gmail.com
Fri Jan 6 08:50:51 CST 2023
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/>
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