On Fri, 2008-10-03 at 12:58 -0500, John Peterson wrote: > On Fri, Oct 3, 2008 at 12:40 PM, Adam C Powell IV <[EMAIL PROTECTED]> wrote: > > On Fri, 2008-10-03 at 10:50 -0500, Roy Stogner wrote: > >> On Thu, 2 Oct 2008, Nasser Mohieddin Abukhdeir wrote: > >> > >> > Moving back to John's point about the previously mentioned > >> > Predictor/Corrector algorithm (assuming we compute everything > >> > correctly), I'm assuming that idea is trashed. > >> > >> The idea that we can use the first Newton step as an explicit solution > >> is wrong, but using a forward Euler solve for the predictor and > >> following it up by a backward Euler Newton solve for the corrector > >> should still work just fine. > > > > Are you sure about that? It seems that if delta t is significantly > > larger than the forward Euler stability criterion, this would make an > > awful predictor. In the past I've used a linear projection of the > > previous two timesteps into the new time as the predictor, and saved a > > couple of Newton iterations vs. using the previous timestep alone, which > > is more stable than a forward Euler step, but doesn't always work well > > either... > > I think this is an interesting question to investigate. As we all > know explicit Euler is unstable when applied repeatedly but just how > "unstable" it is for a single step, and whether a single step is > possibly useful, I'm not so sure.
Good point, the unstable growth of spurious modes in forward Euler is exponential in number of timesteps, but only linear in timestep size. Thanks for the clarification. -Adam -- GPG fingerprint: D54D 1AEE B11C CE9B A02B C5DD 526F 01E8 564E E4B6 Engineering consulting with open source tools http://www.opennovation.com/
signature.asc
Description: This is a digitally signed message part
------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/
_______________________________________________ Libmesh-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-devel
