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

[Barry Smith]

> On Jan 19, 2015, at 1:36 PM, Tobin Isaac <tisaac at ices.utexas.edu> wrote:
> 
> 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?

   Yes. But it appears with regard to sorting we've been rather scattershot on following your logic :-).

   
> 
> 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
>