> On Feb 4, 2017, at 7:35 PM, Matthew Knepley <[email protected]> wrote: > > 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.
Please read one of Petzold's elementary books :-) > > 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
