On Sat, Feb 4, 2017 at 7:44 PM, Jed Brown <[email protected]> wrote: > Matthew Knepley <[email protected]> writes: > > > On Sat, Feb 4, 2017 at 7:24 PM, Zhang, Hong <[email protected]> wrote: > > > >> Can you elaborate a bit more on your problem? > >> > >> If your problem is an index-1 DAE, there is no need to use a projection > >> method, and it is perfectly fine to set it up as a DAE in PETSc. For > >> high-index DAEs, you may have to use TSSetPostStep() to implement your > own > >> projection algorithm. > >> > > > > Please define index. > > Think of it as a measure of singularity of the "mass matrix". Higher > index DAE have more complicated constraints on compatibility of initial > conditions. It's covered in any book or paper on DAEs. >
Both your explanation and Hong's use of the term do not help Gideon (or me) know whether he has an index-1 DAE. There has to be some simple form you can write down so that we can tell. Matt -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
