[petsc-users] question on MatSubMatrixUpdate

[Jed Brown]

Shaohao Chen <shchen at www.phys.lsu.edu> writes:

>I expect "MatSubMatrixUpdate" could do the job better. Am I correct? But I can 
> not find an example of using "MatSubMatrixUpdate" on the website. It is said that the 
> "MatSubMatrixUpdate" is only in a "developer" level and the users should use some other functions to 
> replace it.

You misunderstand MatSubMatrix.  It is a type that represents a
submatrix by applying the full global matrix and restricting the result.
It's mostly interesting when the original matrix is MatShell, MatMFFD,
or some other structured operator that cannot be taken apart.