[petsc-users] Use block Jacobi preconditioner with SNES

[Ali Reza Khaz'ali]

> This is very odd. A sparse linear system of 7K unknowns needs less than a second to be factored. If it is dense, seconds.
> How many nonzero per rows do you have?
> Is 7 thousand the typical size of your blocks in bjacobi?
>
>

There are less than 100 non-zeros per row. 7K was the total size of 
Jacobian matrix. The block sizes of Jacobian are in range of 4-10. I 
could not inform bjacobi about the block sizes (see the communication 
about it please), so it treats the entire Jacobian matrix as one giant 
block.