[petsc-dev] [petsc-maint] Feature: allow unsorted row IS in MatGetSubMatrix_SeqAIJ()

[Tobin Isaac]

If being sorted is a requirement of the interface, I think the ISSorted tests belong in the interface and not in the _SeqAIJ implementation; if it's not a requirement, then only the implementations that don't support unordered IS's should raise an ERR_SUP, right?

On January 19, 2015 12:57:45 PM CST, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>   Should actually send these things to pets-dev
>
>   The docs for MatGetSubMatrix() have the line
>
>"The rows in isrow will be sorted into the same order as the original
>matrix on each process."
>
>    The docs for MatGetSubMatrices() say 
>
>   "Currently both row and column indices must be sorted to guarantee
>   correctness with all matrix types."
>
>PetscErrorCode MatGetSubMatrices_MPIAIJ(Mat C,PetscInt ismax,const IS
>isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
>{
>  PetscErrorCode ierr;
>  PetscInt       nmax,nstages_local,nstages,i,pos,max_no,nrow,ncol;
>PetscBool     
>rowflag,colflag,wantallmatrix=PETSC_FALSE,twantallmatrix,*allcolumns;
>
>  PetscFunctionBegin;
>/* Currently, unsorted column indices will result in inverted column
>indices in the resulting submatrices. */
>/* It would make sense to error out in
>MatGetSubMatrices_MPIAIJ_Local(), the most impl-specific level.
>However, there are more careful users of
>MatGetSubMatrices_MPIAIJ_Local() -- MatPermute_MPIAIJ() -- that
>take care to order the result correctly by assembling it with
>MatSetValues() (after preallocating).
>   */
>  for (i = 0; i < ismax; ++i) {
>    PetscBool sorted;
>    ierr = ISSorted(iscol[i], &sorted);CHKERRQ(ierr);
>if (!sorted) SETERRQ1(PETSC_COMM_SELF, PETSC_ERR_SUP, "Column index set
>%D not sorted", i);
>  }
>
>In other words the sorted business seems a little wacky at the moment. 
>I'm not sure what to conclude.
>
>
>   Barry
>
>> On Jan 19, 2015, at 11:36 AM, Tobin Isaac <tisaac at ices.utexas.edu>
>wrote:
>> 
>> 
>> There doesn't seem to be any reason for MatGetSubMatrix_SeqAIJ() to
>> require the row IS to be sorted, and this requirement differs from
>> other implementations, e.g. _MPIAIJ.  I have a feature branch that
>> removes the requirement.  Can I merge it into next for testing?
>> 
>> Thanks,
>>  Toby