blocked index sets

[Barry Smith]

On Aug 27, 2008, at 2:26 PM, Matthew Knepley wrote:

> On Wed, Aug 27, 2008 at 2:10 PM, Barry Smith <bsmith at mcs.anl.gov>  
> wrote:
>>  Even if an object (class) has NO collective operations, if, when  
>> you use
>> that object, you must have partners are all
>> other processes in a MPI_Comm then I think it is a good approach to  
>> have
>> that be a parallel
>> object that shares the comm.
>
> I will not suggest that we go back on IS now. However, I am not sure  
> I buy the
> above argument. I see IS as just managing a list of integers, and
> maybe reporting
> some local properties. All the parallel actions are done by different
> objects, like
> Scatter or Mat. This is different from KSP or Vec which have natural
> parallel actions.
>

    I understand your explanation and appreciate it. As I continue to  
screw around with the "multi-physics"
stuff I envision more use of the IS where manipulations with the IS  
don't always
occur in the context of a Vec or Mat, in that case having the comm  
within the IS
is very powerful. (It may turn out that this never really happens so  
we could remove the
comm from the IS, I can't say yet.)

    Barry


>   Matt
>
>> Barry
> -- 
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which
> their experiments lead.
> -- Norbert Wiener
>