[petsc-dev] FieldSplit restrictions

[Jed Brown]

Is there a case for putting a field in more than one split?  The current
implementation allows this, but it makes it easier to accidentally have
more splits than you wanted.  The underlying challenge for Doing the
Right Thing is that the type is not normally set until
PCSetFromOptions().  Any calls to PCFieldSplitSet* will be ignored prior
to this.  The problem occurs when the user specifies
-pc_fieldsplit_*_fields AND the code adds splits with
PCFieldSplitSet(IS|Fields).  This used to create a bunch of splits which
is probably not what anyone asked for, I just pushed a some code that
makes command-line split definitions permanent.  This isn't entirely
satisfactory because there isn't currently a way to get rid of them, but
it's better than having lots of spurious splits.

Lisandro, let me know if the current code behaves the way you expect.

Jed