On Wed, Dec 14, 2011 at 9:31 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> > 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. > We could support a matrix-free SNESVI if extracting a submatrix from a MF matrix was implemented by pre-/post-multiplying it by a suitable P, no? Dmitry. > > Barry > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20111214/16e69225/attachment.html>