[petsc-users] MatChop

[Stefano Zampini]

> On 21 May 2021, at 7:49 PM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Fri, May 21, 2021 at 12:33 PM Stefano Zampini <stefano.zampini at gmail.com <mailto:stefano.zampini at gmail.com>> wrote:
> 
> 
>> On 21 May 2021, at 7:17 PM, Pierre Jolivet <pierre at joliv.et <mailto:pierre at joliv.et>> wrote:
>> 
>> 
>> 
>>> On 21 May 2021, at 6:03 PM, Stefano Zampini <stefano.zampini at gmail.com <mailto:stefano.zampini at gmail.com>> wrote:
>>> 
>>> Emmanuel
>>> 
>>> thanks for reporting this.
>>> I believe we have a regression in MatChop from https://gitlab.com/petsc/petsc/-/commit/038df967165af8ac6c3de46a36f650566a7db07c <https://gitlab.com/petsc/petsc/-/commit/038df967165af8ac6c3de46a36f650566a7db07c> (cc'ing Pierre)
>>> We call MatAssemblyBegin/End within the row loop. Also. I don't understand why we need to check for  r < rend herre https://gitlab.com/petsc/petsc/-/blob/038df967165af8ac6c3de46a36f650566a7db07c/src/mat/utils/axpy.c#L513 <https://gitlab.com/petsc/petsc/-/blob/038df967165af8ac6c3de46a36f650566a7db07c/src/mat/utils/axpy.c#L513>. nor why we need to allocate newCols (can use cols)
>> 
>> That part is from the initial 8-year old implementation from Matt (https://gitlab.com/petsc/petsc/-/commit/4325cce7191c5c61f4f090c59eaf6773fdee7b48#9d78409dea8190bffda8b68fee5aef233dc1c677 <https://gitlab.com/petsc/petsc/-/commit/4325cce7191c5c61f4f090c59eaf6773fdee7b48#9d78409dea8190bffda8b68fee5aef233dc1c677>).
>> You need the check otherwise this error is raised: https://www.mcs.anl.gov/petsc/petsc-current/src/mat/interface/matrix.c.html#line566 <https://www.mcs.anl.gov/petsc/petsc-current/src/mat/interface/matrix.c.html#line566>.
> 
> I see, anyway you do not need the check if the loop range [rStart,rEnd). So now I don’t understand why the loop must be [rStart,rStart+maxRows], Matt?
> 
> It is terrible, but I could not see a way around it. We want to use MatGetRow() for each row, but that requires an assembled matrix.

What is the use case for calling MatChop on an unassembled matrix ?

> We want to use
> MatSetValues() to changes things, but that unassembles the matrix, so we need an assembly at each iteration, but assembly is collective, so everyone has
> to take the same number of iterations. Thus, maxRows.


> 
>    Matt 
>> Thanks,
>> Pierre
>> 
>>> Pierre, can you take a look?
>>> 
>>> Il giorno ven 21 mag 2021 alle ore 18:49 Emmanuel Ayala <juaneah at gmail.com <mailto:juaneah at gmail.com>> ha scritto:
>>> Hi everybody,
>>> 
>>> I just updated petsc from version 13 to 15. Before the update everything works well, then my code give me an error:
>>> 
>>> [9]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
>>> [9]PETSC ERROR: Invalid argument
>>> [9]PETSC ERROR: Setting off process row 53484 even though MatSetOption(,MAT_NO_OFF_PROC_ENTRIES,PETSC_TRUE) was set
>>> [9]PETSC ERROR: See https://www.mcs.anl.gov/petsc/documentation/faq.html <https://www.mcs.anl.gov/petsc/documentation/faq.html> for trouble shooting.
>>> [9]PETSC ERROR: Petsc Release Version 3.15.0, Mar 30, 2021 
>>> [9]PETSC ERROR: ./comp on a arch-linux-c-opt-O2-superlud_mumps_hyp named eayala by ayala Fri May 21 10:40:36 2021
>>> [9]PETSC ERROR: Configure options --with-debugging=0 COPTFLAGS="-O2 -march=native -mtune=native" CXXOPTFLAGS="-O2 -march=native -mtune=native" FOPTFLAGS="-O2 -march=native -mtune=native" --download-mpich --download-hypre --download-mumps --download-scalapack --download-parmetis --download-metis --download-superlu_dist --download-cmake --download-fblaslapack=1 --with-cxx-dialect=C++11
>>> 
>>> The error appears after a matrix assembly, the matrix was created with DMCreateMatrix and updated with MatSetValuesLocal.
>>> 
>>> A Little work around I found the solution, avoid using MatChop on this matrix, but I still need to use MatChop. There is any reason to have this problem?
>>> 
>>> Thanks in advance.
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> -- 
>>> Stefano
>> 
> 
> 
> 
> -- 
> 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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