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
