On Dec 14, 2011, at 9:22 PM, Jed Brown wrote: > On Wed, Dec 14, 2011 at 17:55, Barry Smith <bsmith at mcs.anl.gov> wrote: > What Matt is trying to tell you is that changing values at this level to > prevent function evaluations outside of the function domain inside Newton is > a total hack that rarely works well and should be avoided. You really don't > want to do this. > > It sounds like for the problems Bobby is asking about, the continuum > solutions never produce values at a "constraint". In gas dynamics, the > continuum equations are PDEs, not variational inequalities, but the pressure > and temperature are still never negative. If a bound was available, MatMFFD > could potentially choose the sign of the differencing to stay within the > feasible domain. This does seem quite limited, however, because the positive > and negative versions could cause violations in different parts of the domain.
If you are truly near 0 in temperature or pressure and differencing can push you over the limit then I submit it is perfectly reasonable to solve them as VI. Though actually our VI solvers are currently not really matrix-free so this is a bit academic. Barry
