[petsc-dev] Very Useful Description of MAT Types in Petsc Index

[Junchao Zhang]

Even better, with examples showing a small matrix.
--Junchao Zhang


On Thu, Mar 26, 2020 at 2:26 PM Jacob Faibussowitsch <jacob.fai at gmail.com>
wrote:

> Hello,
>
> In keeping with PETSc design it would be nice to have *more* detail for
> all MAT implementations explaining in what the letters stand for, and
> use-cases it might be useful for. For example:
>
> MATAIJSELL
> <https://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MATAIJSELL.html#MATAIJSELL>
> = "AIJSELL" - A matrix type to be used for sparse matrices. This matrix
> type is identical to MATSEQAIJSELL when constructed with a single process
> communicator, and MATMPIAIJSELL otherwise. As a result, for single process
> communicators, MatSeqAIJSetPreallocation
> <https://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MatSeqAIJSetPreallocation.html#MatSeqAIJSetPreallocation>()
> is supported, and similarly MatMPIAIJSetPreallocation
> <https://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MatMPIAIJSetPreallocation.html#MatMPIAIJSetPreallocation>()
> is supported for communicators controlling multiple processes. It is
> recommended that you call both of the above preallocation routines for
> simplicity.
>
>
> I am no complete beginner but I am no computational matrix expert either.
> I have no idea what “SELL” is. Obviously googling "mat sell format” gives
> less than useful results. Other such types are MATAIJCRL, MATAIJMKL,
> MATAIJPERM, MATADJ.
>
> Smallest change could be as simple as mirroring MATSBAIJ, which is clear
> and concise:
>
> MATMPISBAIJ
> <https://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MATMPISBAIJ.html#MATMPISBAIJ>
> = "mpisbaij" - A matrix type to be used for distributed symmetric sparse
> block matrices, based on block compressed sparse row format. Only the upper
> triangular portion of the "diagonal" portion of the matrix is stored. For
> complex numbers by default this matrix is symmetric, NOT Hermitian
> symmetric. To make it Hermitian symmetric you can call MatSetOption
> <https://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MatSetOption.html#MatSetOption>
> (Mat
> <https://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/Mat.html#Mat>,
> MAT_HERMITIAN
> <https://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MatOption.html#MatOption>
> );
>
>
> Clearest case would be:
>
> MATMPISBAIJ = "mpisbaij" - *MATrix MPI Symmetric Block AIJ.* A matrix
> type to be used for distributed symmetric sparse block matrices, based on
> block compressed sparse row format.
>
> Only the upper triangular portion of the "diagonal" portion of the matrix
> is stored. For complex numbers by default this matrix is symmetric, NOT
> Hermitian symmetric. To make it Hermitian symmetric you
> can call MatSetOption(Mat, MAT_HERMITIAN);
>
>
> Each format is useful in its own case, but people can’t use things if they
> don’t know what it is!
>
> Best regards,
>
> Jacob Faibussowitsch
> (Jacob Fai - booss - oh - vitch)
> Cell: (312) 694-3391
>
>
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