On Sat, Feb 4, 2017 at 7:56 PM, Zhang, Hong <[email protected]> wrote:
> On Feb 4, 2017, at 7:47 PM, Matthew Knepley <[email protected]> wrote: > > 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. > > > This is why we need to learn more about Gideon's problem. It is easy to > determine the index if he can write down his problem in a simple form. But > it is not that easy the other way round. > He says y' = f(y) 0 = g(y) which appears to me to be a Hessenberg index-2 DAE. Is that correct? Matt Hong > > > 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 > > > -- 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
