[petsc-users] Recursive field split with MatNest

[Jed Brown]

Colin McAuliffe <cjm2176 at columbia.edu> writes:

> I'd be interested in implementing this, I think I should have some time to
> spend on it in a few weeks. I suppose the ISSubset function should
> determine which ISs were used to make up a third IS? Can this be done by
> having ISSum attach a list of pointers to the constituent ISs to the summed
> IS for retrieval by ISSubset?

It could and that would probably be fairly harmless in terms of peak
memory usage.  An alternative would be to compute a cryptographic hash
of the index sets and only store that.  This would allow comparison
without needing to flatten the index sets to arrays of integers (see
current implementation of ISEqual).
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