> On Tue, 28 Sep 2010, John Peterson wrote: > >> I have a local change fixing the setting of the time variable in the >> FEM/DiffContext. >> >> In order to do that, I needed access to the "deltat" variable from the >> System which created the FEMContext. >> >> The approach I'm currently using requires the creating System be >> derived from a FEMSystem, so that the existence of deltat is >> guaranteed. We discussed moving deltat to System itself so that this >> assumption is no longer required, but IIRC correctly you weren't >> super-enthusiastic about that solution, since forcing a deltat >> parameter on the base System class (which may represent a steady set >> of equations) was less than desirable. >> >> Should I go ahead and move deltat to System, or did you have something >> else in mind? Alternatively we could wait until after the release, >> but this does fix a potential bug in FEMContext so it might be good to >> get out now. > > Damn, I'd forgotten about that one. I'd rather fix it now, certainly; > otherwise we're killing higher-order time discretization accuracy for > anyone whose FEMSystem physics depends directly on t and not just on > d/dt. > > Double damn. I just realized I was describing an undiagnosed problem > that Paul Bauman saw; I'll Cc: this to him. > > > But although a bad fix would be better than no fix, I'd still like to > avoid an aesthetically bad fix, so let's try to brainstorm other > options first. > > Perhaps give DiffContext a Real* _delta_t member variable, default > NULL, with setter/getter options? build_context() in a DiffSystem > would assign that to the system delta_t, users with their own > transient systems could assign it instead to their own time step, and > we'd just have to test for NULL before using it within DiffContext or > a subclass. > > David, any thoughts? You and the other RB folks are probably the only > ones currently using DiffContext in transient systems other than > DiffSystem.
Your Real* _delta_t idea would work fine in the RB context too, so I'd be happy with that. David ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Libmesh-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-devel
