I want to use MatGetLocalSubMatrix for assembly purpose.
PetscErrorCode MatGetLocalSubMatrix(Mat mat,IS isrow,IS iscol,Mat *submat)
I want to get a submat shared by some (not all) of the processes that share the
mat.
Some questions.
1. Shall I create isrow and iscol shared by the processes that will share the
submat?
2. The manual says the submat supports MatSetValuesLocal. Is the
LocalToGlobalMapping already defined for submat, or I need to define it by
myself?
If it is already defined, is it derived from the ltog of the mat such that
for this processor the local numbering of the submat are in the same order
as the local numbering for the mat?
