On Tue, Feb 12, 2013 at 11:17 PM, Matthew Knepley <knepley@gmail.com> wrote:

Yes. PetscSection represents groups of numbers, and you can see the grouping.

IS is a map from (int) -> (int), but PetscSection is a map from (int) -> (int,int) where the pair is interpreted to mean an interval of non-negative extent. If it's any use, an IS could be thought of as the special case (int) -> (int,1).

What queries "do not just return members of this list" in PETSc section? (That is queries we wish to retain anyways).

For example, you can ask "how many items are in group p?". This is crucial, and the whole point of the structure.

I don't see how you can recover that information from just the list of dof numbers.