[petsc-users] Scaling GMRES residual

[Jed Brown]

On Tue, Jun 26, 2012 at 2:31 PM, Colin McAuliffe <cjm2176 at columbia.edu>wrote:

> Hello,
>
> I would like to use GMRES for a monolithic solution of a multiphysics
> problem. There are drastically different units in the problem and so the
> residual norm is dominated by the terms with the largest units. Is there a
> way to tell petsc to scale the residual before taking the norm to avoid
> this?
>

You can "fix" it with preconditioning, but then you can only use the
preconditioned residual. You should really fix the units when formulating
the problem. (This does not require formal nondimensionalization, just
introduced units so that state and residuals are of order 1.)
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