[petsc-users] MatGetLocalSubMatrix?

[Mark Adams]

I have a 4x4 block matrix, in one big AIJ matrix.  I use (global) ISs to
address individual fields.  I have a mass matrix for one field.  I would
like to add a scaled mass matrix to one field at a time.

MatGetLocalSubMatrix looks like what I want but it takes local indices.  My
ISs are global.  It seems like I should be able to do this without making a
local IS (shift the IS by the first equation index for the process).  Am I
missing something?

Mark
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