It looks like this was copied from the AIJ format but is never used for 
BAIJ. Could probably be removed.


   Barry


> On Feb 22, 2018, at 6:55 AM, Xiangdong <epsco...@gmail.com> wrote:
> 
> Hello everyone,
> 
> I am curious about the purpose of mdiag in MatInverseBlockDiagonal_SeqBAIJ
> 
> http://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/baij/seq/baij.c.html
> 
> It seems that the inverse of the diagonal block is stored is a->idiag, and 
> the extra copy of diagonal block itself is stored in mdiag or  
> a->idiag+bs2*mbs. What is the purpose of storing this mdiag as an extra copy 
> of diagonal block? When will this mdiag be used?
> 
> Thank you.
> 
> Best,
> Xiangdong
> 
> 
> if (!a->idiag) {
>  38:     PetscMalloc1(2*bs2*mbs,&a->idiag);
>  39:     PetscLogObjectMemory((PetscObject)A,2*bs2*mbs*sizeof(PetscScalar));
>  40:   }
>  41:   diag  = a->idiag;
>  42:   mdiag = a->idiag+bs2*mbs;
> 
> 
> 138:     for (i=0; i<mbs; i++) {
> 139:       odiag  = v + bs2*diag_offset[i];
> 140:       PetscMemcpy(diag,odiag,bs2*sizeof(PetscScalar));
> 141:       PetscMemcpy(mdiag,odiag,bs2*sizeof(PetscScalar));
> 142:       
> PetscKernel_A_gets_inverse_A(bs,diag,v_pivots,v_work,allowzeropivot,&zeropivotdetected);
> 143:       if (zeropivotdetected) A->factorerrortype = 
> MAT_FACTOR_NUMERIC_ZEROPIVOT;
> 144:       diag  += bs2;
> 145:       mdiag += bs2;
> 

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