[petsc-users] -ksp_diagonal_scale

[Jed Brown]

On Fri, Dec 23, 2011 at 12:52, Dominik Szczerba <dominik at itis.ethz.ch>wrote:

> I am scaling my systems when dealing with small (microscopic) scales
> in SI dimensions.
>

The best choice is to choose suitable units so that the system is
intrinsically well-scaled.


> This is because otherwise I have very small (near
> epsilon) entries in the matrix and the solution fails or takes
> significantly longer to converge. I used to do it by hand so far, if
> there is a way to do it in Petsc - especially automatically detecting
> the optimal scale - I am all ears.
>

You are best off doing it by hand, it is better to avoid
-ksp_diagonal_scale when it's reasonable to do so. If you have trouble
determining a reasonable scale at assembly time, it might make sense to use.
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