[petsc-users] MatCreateSBAIJ

[Sam Guo]

Mark, thanks for the quick response. I am more interested in parallel
implementation of MatMult for SBAIJ. I found following

1094: *PetscErrorCode
<https://petsc.org/main/docs/manualpages/Sys/PetscErrorCode.html#PetscErrorCode>
MatMult_MPISBAIJ(Mat
<https://petsc.org/main/docs/manualpages/Mat/Mat.html#Mat> A,Vec
<https://petsc.org/main/docs/manualpages/Vec/Vec.html#Vec> xx,Vec
<https://petsc.org/main/docs/manualpages/Vec/Vec.html#Vec> yy)*1095:
{1096:   Mat_MPISBAIJ      *a = (Mat_MPISBAIJ*)A->data;1097:
PetscErrorCode <https://petsc.org/main/docs/manualpages/Sys/PetscErrorCode.html#PetscErrorCode>
   ierr;1098:   PetscInt
<https://petsc.org/main/docs/manualpages/Sys/PetscInt.html#PetscInt>
       mbs=a->mbs,bs=A->rmap->bs;1099:   PetscScalar
<https://petsc.org/main/docs/manualpages/Sys/PetscScalar.html#PetscScalar>
      *from;1100:   const PetscScalar
<https://petsc.org/main/docs/manualpages/Sys/PetscScalar.html#PetscScalar>
*x;
1103:   /* diagonal part */1104:
(*a->A->ops->mult)(a->A,xx,a->slvec1a);1105:   VecSet
<https://petsc.org/main/docs/manualpages/Vec/VecSet.html#VecSet>(a->slvec1b,0.0);
1107:   /* subdiagonal part */1108:
(*a->B->ops->multtranspose)(a->B,xx,a->slvec0b);
1110:   /* copy x into the vec slvec0 */1111:   VecGetArray
<https://petsc.org/main/docs/manualpages/Vec/VecGetArray.html#VecGetArray>(a->slvec0,&from);1112:
  VecGetArrayRead
<https://petsc.org/main/docs/manualpages/Vec/VecGetArrayRead.html#VecGetArrayRead>(xx,&x);
1114:   PetscArraycpy
<https://petsc.org/main/docs/manualpages/Sys/PetscArraycpy.html#PetscArraycpy>(from,x,bs*mbs);1115:
  VecRestoreArray
<https://petsc.org/main/docs/manualpages/Vec/VecRestoreArray.html#VecRestoreArray>(a->slvec0,&from);1116:
  VecRestoreArrayRead
<https://petsc.org/main/docs/manualpages/Vec/VecRestoreArrayRead.html#VecRestoreArrayRead>(xx,&x);
1118:   VecScatterBegin
<https://petsc.org/main/docs/manualpages/PetscSF/VecScatterBegin.html#VecScatterBegin>(a->sMvctx,a->slvec0,a->slvec1,ADD_VALUES
<https://petsc.org/main/docs/manualpages/Sys/ADD_VALUES.html#ADD_VALUES>,SCATTER_FORWARD
<https://petsc.org/main/docs/manualpages/Vec/SCATTER_FORWARD.html#SCATTER_FORWARD>);1119:
  VecScatterEnd
<https://petsc.org/main/docs/manualpages/PetscSF/VecScatterEnd.html#VecScatterEnd>(a->sMvctx,a->slvec0,a->slvec1,ADD_VALUES
<https://petsc.org/main/docs/manualpages/Sys/ADD_VALUES.html#ADD_VALUES>,SCATTER_FORWARD
<https://petsc.org/main/docs/manualpages/Vec/SCATTER_FORWARD.html#SCATTER_FORWARD>);1120:
  /* supperdiagonal part */1121:
(*a->B->ops->multadd)(a->B,a->slvec1b,a->slvec1a,yy);1122:
return(0);1123: }

  I try to understand the algorithm.


Thanks,

Sam


On Mon, Mar 21, 2022 at 11:14 AM Mark Adams <mfadams at lbl.gov> wrote:

> This code looks fine to me and the code is
> in src/mat/impls/sbaij/seq/sbaij2.c
>
> On Mon, Mar 21, 2022 at 2:02 PM Sam Guo <sam.guo at cd-adapco.com> wrote:
>
>> Dear PETSc dev team,
>>    The documentation about MatCreateSBAIJ has following
>> "It is recommended that one use the MatCreate
>> <https://petsc.org/main/docs/manualpages/Mat/MatCreate.html#MatCreate>
>> (), MatSetType
>> <https://petsc.org/main/docs/manualpages/Mat/MatSetType.html#MatSetType>()
>> and/or MatSetFromOptions
>> <https://petsc.org/main/docs/manualpages/Mat/MatSetFromOptions.html#MatSetFromOptions>(),
>> MatXXXXSetPreallocation() paradigm instead of this routine directly.
>> [MatXXXXSetPreallocation() is, for example, MatSeqAIJSetPreallocation
>> <https://petsc.org/main/docs/manualpages/Mat/MatSeqAIJSetPreallocation.html#MatSeqAIJSetPreallocation>
>> ]"
>>    I currently call MatCreateSBAIJ directly as follows:
>> MatCreateSBAIJ (with d_nnz and o_nnz)
>> MatSetValues (to add row by row)
>> MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
>> MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
>> MatSetOption(A, MAT_SYMMETRIC, PETSC_TRUE);
>>
>>    Two questions:
>>    (1) I am wondering whether what I am doing is the most efficient.
>>
>>    (2) I try to find out how the matrix vector multiplication is
>> implemented in PETSc for SBAIJ storage.
>>
>> Thanks,
>> Sam
>>
>
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