On Feb 4, 2017, at 7:35 PM, Matthew Knepley <[email protected]<mailto:[email protected]>> wrote:
On Sat, Feb 4, 2017 at 7:24 PM, Zhang, Hong <[email protected]<mailto:[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. http://www.scholarpedia.org/article/Differential-algebraic_equations#Index Hong 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]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[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
