On Mon, Jul 9, 2012 at 11:23 AM, Colin McAuliffe <cjm2176 at columbia.edu>wrote:
> Ok thanks, I can see how introducing units to the residual is necessary, > but when would it be necessary to introduce units to the state? I would > imagine this would only be needed if a numerically differentiated jacobian > was being used. > It depends if you care about symmetry and if you want the step tolerance to be meaningful. It can also affect scaling of boundary conditions. > > Thanks > Colin > > > Quoting Jed Brown <jedbrown at mcs.anl.gov>: > > 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.) >> >> > > > -- > Colin McAuliffe > PhD Candidate > Columbia University > Department of Civil Engineering and Engineering Mechanics > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120709/c52ca38b/attachment.html>
