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. Matt > If you happen to have a Hamiltonian system to solve, I have a symplectic > solver in my own branch that you can use directly. > > Hong (Mr.) > > On Feb 4, 2017, at 9:47 AM, Gideon Simpson <[email protected]> > wrote: > > Would setting it up as a DAE in petsc be algorithmically euivalent to a > projected method (i.e., step of standard RK followed by nonlinear > projection)? > > -gideon > > On Feb 3, 2017, at 11:47 PM, Matthew Knepley <[email protected]> wrote: > > That is one answer. Another one is that this particular system is a DAE > and we have methods for that. > > Matt > > On Fri, Feb 3, 2017 at 8:40 PM, Barry Smith <[email protected]> wrote: > >> >> TSSetPostStep(); in your function use TSGetSolution() to get the current >> solution. >> >> Please let us know how it works out >> >> Barry >> >> >> >> > On Feb 3, 2017, at 7:14 PM, Gideon Simpson <[email protected]> >> wrote: >> > >> > I’m interested in implementing a projection method for an ODE of the >> form: >> > >> > y’ = f(y), >> > >> > such that g(y) = 0 for all time (i.e., g is conserved). Note that in a >> projection method, a standard time step is made to produce y* from y_{n}, >> and then this is corrected to obtain y_{n+1} satisfying g(y) = 0. >> > >> > There were two ways I was thinking of doing this, and I was hoping to >> get some input: >> > >> > Idea 1: Manually loop through using taking a time step and then >> implementing the projection routine. I see that there is a TSStep command, >> but this doesn’t seem to be much documentation on how to use it in this >> scenario. Does anyone have any guidance? >> > >> > Idea 2: Is there some analog to TSMonitor that allows me to modify the >> solution after each time step, instead of just allowing for some >> computation of a statistic? >> > >> > >> >> > > > -- > 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
