[petsc-users] Vec Ownership ranges with Global Section Offsets
Nicholas Arnold-Medabalimi
narnoldm at umich.edu
Fri Jan 6 08:36:42 CST 2023
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
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
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