[petsc-users] Use block Jacobi preconditioner with SNES

[Jed Brown]

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

>> 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.

This should take on the order of a second to solve with a sparse direct
solver.  What shape is your domain?  Can you send a solver profile and
output from running with -snes_view -log_view?