[petsc-users] [petsc-dev] MatPreallocatorPreallocate segfault with PETSC 3.16

[Jed Brown]

MatPreallocator stores "the nonzero structure" in a hash table so it can be easily updated. A normal Mat stores it in a compressed (CSR) format that is expensive to update.

Marius Buerkle <mbuerkle at web.de> writes:

> Ok. I did not know that. I was under the impression that MatPreallocator does actually not allocate the nonzeros and just stores the nonzero structure. But if this is not the case then of course I just duplicate the matrix.
>
> Thanks for the feedback.
>
>> Gesendet: Donnerstag, den 03.02.2022 um 03:09 Uhr
>> Von: "Jed Brown" <jed at jedbrown.org>
>> An: "Marius Buerkle" <mbuerkle at web.de>, "Patrick Sanan" <patrick.sanan at gmail.com>
>> Cc: "PETSc users list" <petsc-users at mcs.anl.gov>, petsc-dev <petsc-dev at mcs.anl.gov>
>> Betreff: Re: Aw: Re: [petsc-dev] [petsc-users] MatPreallocatorPreallocate segfault with PETSC 3.16
>>
>> Marius Buerkle <mbuerkle at web.de> writes:
>>
>> > Thanks for they reply. Yes the example works, this is how I was doing it before. But the matrix is rather big and i need a matrix with the same structure at various points in my code. So it was convenient to create the matrix with preallocate, destroy it after using it to free the memory and creating it again later with the same preallocate.
>> > Anyway it works with MatDuplicate for now.
>>
>> I think it should take *less* memory to destroy the preallocator and duplicate the actual matrix than to destroy the matrix and persist the preallocator. If that is not the case (or close enough), we can make it so.