[petsc-users] KSPSetDiagonalScale

[Colin McAuliffe]

Using the direct solver as a preconditioner I can't seem to find any  
difference between the results with -ksp_diagonal_scale vs the results  
without this option.  I also cant tell if the diagonal scaling is  
actually being applied in this case.


Quoting Jed Brown <five9a2 at gmail.com>:

> It just means that both matrix arguments A and B are the same.
>
> What happens if you use this direct solver as a preconditioner?
> On May 17, 2012 2:23 PM, "Colin McAuliffe" <cjm2176 at columbia.edu> wrote:
>
>> Hello!
>>
>> I am solving a coupled multiphysics problem which has several different
>> units, which leads to a poorly conditioned jacobian. I am using the
>> following ksp options:
>>
>> -ksp_type preonly -pc_type lu -pc_factor_mat_solver_package umfpack
>>
>> The results I am getting are not right and I suspect that the conditioning
>> of the jacobian may be playing a part in that. I would like to improve the
>> conditioning by using -ksp_diagonal_scale, but adding it does not seem to
>> help. The documentation for this option says 'this routine is only used if
>> the matrix and preconditioner matrix are the same thing'.
>>
>> Does that mean the command can only be used with no preconditioner?
>>
>> http://www.mcs.anl.gov/petsc/**petsc-current/docs/**manualpages/KSP/**
>> KSPSetDiagonalScale.html<http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetDiagonalScale.html>
>>
>> All the best,
>>
>> --
>> Colin McAuliffe
>> PhD Candidate
>> Columbia University
>> Department of Civil Engineering and Engineering Mechanics
>>
>



-- 
Colin McAuliffe
PhD Candidate
Columbia University
Department of Civil Engineering and Engineering Mechanics