[petsc-dev] [petsc-users] Any suggestion for this kinds of matrix?

[Jed Brown]

Mark, YOU obtained a matrix with poorly scaled boundary conditions (by a
cool factor of 1e13). Some people use penalties which is worse. The
preconditioned norm fixes the scaling. We used -ksp_diagonal_scale to
actually modify the matrix entries, but that is a bit fragile/restrictive.

I think we would have just as much confusion on petsc-maint/users (from the
residual dropping abruptly on the first iteration) if we made
unpreconditioned the default.
On Nov 10, 2011 7:50 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:

>
> On Nov 10, 2011, at 5:12 PM, Mark F. Adams wrote:
>
> >
> >>
> >
> > Would this problem also be fixed with -ksp_norm_type unpreconditioned ???
> >
> > In that case you could make this the default for debug and not debug,
> which is cleaner (I've never figured out why you even offer preconditioned
> norm as an option, much less the default)
> >
>
>   Someday I'll have to write a paper showing why :-)
>
>
>
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