[petsc-users] fieldsplit: Unhandled case, must have at least two fields, not 1!

[Jed Brown]

Nico Schlömer <nico.schloemer at gmail.com> writes:

> Hi Jed,
>
> thanks for the quick answer!
> I can of course generate the strided index sets (01x34x6...,
> xx2xx5x...) myself and insert them via PCFieldSplitSetIS(), but I
> thought that ultimately does the same thing that I would have liked
> PCFieldSplitSetFields() to do for me. Not true?

PCFieldSplitSetFields is something you call only once to identify all
the fields.  It doesn't let you group multiple strides in one, so you
could create "ux", "uy", and "p", but then those would be separate.  You
can create splits using numbers, -fieldsplit_block_size 3
-fieldsplit_0_fields 0,1 -fieldsplit_1_fields 2 (assuming collocated
discretization), but this can be rather opaque to maintain.
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