[petsc-users] questions on BAIJ matrix

[Xiangdong]

On Thu, Jun 8, 2017 at 3:17 PM, Hong <hzhang at mcs.anl.gov> wrote:

> Xiangdong:
> MatCreateMPIBAIJWithArrays() is obviously buggy, and not been tested.
>
>
>> 1) In the remark of the function MatCreateMPIBAIJWithArrays, it says " bs -
>> the block size, only a block size of 1 is supported". Why must the block
>> size be 1? Is this a typo?
>>
>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/
>> Mat/MatCreateMPIBAIJWithArrays.html
>>
>
> It seems only bs=1 was implemented. I would not trust it without a test
> example.
>
>>
>> 2) In the Line 4040 of the implemention of MatCreateMPIBAIJWithArrays,
>> would the matrix type be matmpibaij instead of matmpiSbaij?
>>
>
> This is an error. It should be matmpibaij.
>
>>
>> http://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/bai
>> j/mpi/mpibaij.c.html#MatCreateMPIBAIJWithArrays
>>
>> 4031: PetscErrorCode  MatCreateMPIBAIJWithArrays(MPI_Comm comm,PetscInt
>> bs,PetscInt m,PetscInt n,PetscInt M,PetscInt N,const PetscInt i[],const
>> PetscInt j[],const PetscScalar a[],Mat *mat)
>> 4032: {
>>
>> 4036:   if (i[0]) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"i
>> (row indices) must start with 0");
>> 4037:   if (m < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"local
>> number of rows (m) cannot be PETSC_DECIDE, or negative");
>> 4038:   MatCreate(comm,mat);
>> 4039:   MatSetSizes(*mat,m,n,M,N);
>> 4040:   MatSetType(*mat,MATMPISBAIJ);
>>
>
>  It should be MATMPIBAIJ.
>
>>
>> 3) I want to create a petsc matrix M equivalent to the sum of two block
>> csr matrix/array (M1csr, M2csr). What is the best way to achieve it? I am
>> thinking of created two petsc baij matrix (M1baij and M2baij) by
>> calling MatCreateMPIBAIJWithArrays twice and then call MATAXPY to get
>> the sum M=M1baij + M2baij. Is there a better way to do it?
>>
>
> This is an approach. However  MatCreateMPIBAIJWithArrays() needs to be
> fixed, tested and implemented with requested bs. What bs do you need?
>

Why does each bs need to be implemented separately? In the mean time, I
modifed the implementation of MatCreateMPIBAIJWithArrays() a little bit to
create a baij matrix with csr arrays.

MatCreate(comm,mat);
MatSetSizes(*mat,m,n,M,N);
MatSetType(*mat,MATMPIBAIJ);
MatMPIBAIJSetPreallocationCSR(*mat,bs,i,j,a);
MatSetOption(*mat,MAT_ROW_ORIENTED,PETSC_FALSE);
MatAssemblyBegin(M,MAT_FINAL_ASSEMBLY);
MatAssemblyEnd(M,MAT_FINAL_ASSEMBLY);

I just set the type to MATMPIBAIJ and delete the line MatSetOption before
preallocation (otherwise I get error at runtime complaining using set
options before preallocation) and it works fine. The only thing missing is
that setting mat_row_oriented to be petsc_false has no effect on the final
matrix, which I do not know how to fix.



>
> Why not use MatCreate(), MatSetValuses() (set a block values at time) to
> create two MPIBAIJ matrices, then call MATAXPY. Since petsc MPIBAIJ matrix
> has different internal data structure than csr,
> "The i, j, and a arrays ARE copied by MatCreateMPIBAIJWithArrays() into
> the internal format used by PETSc;", so this approach would give similar
> performance.
>

I will try this option as well. Thanks for your suggestions.

Xiangdong

>
> Hong
>
>
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