[petsc-users] Use block Jacobi preconditioner with SNES

[Jed Brown]

Ali Reza Khaz'ali <arkhazali at cc.iut.ac.ir> writes:

>> MATNEST is only a storage optimization after everything works right. 
>> It does
>> not have to do with solving.
> Thanks for the answer. I hoped that I could use block solvers suited for 
> MATNEST, which apparently work for a variable-sized block matrix. To the 
> extend of my knowledge, MatCreateBAIJ only accepts constant block sizes.

The BAIJ blocks are usually grouping of fields for each discretization
"point".  NEST is usually grouping different fields with which you want
to use different sparse solution strategies (e.g., algebraic multigrid
on some, a simpler solver on others).