> On Feb 12, 2017, at 11:30 AM, Gideon Simpson <gideon.simp...@gmail.com> wrote: > > I’ve begun working on implementing a projected time stepping method for > solving y’ = f(y), where g(y(t)) is an invariant of the flow. Per a previous > email exchange, it was suggested that I use TSSetPostStep to perform the > projection routine, calling TSGetSolution obtain the current iterate, which > will be corrected with the projection. However, I noticed two things: > > 1. The documentation for TSGetSolution says "This vector not changed until > the solution at the next timestep has been calculated.” Does that mean that > if I make a change to the solution in a PostStep function, it won’t be > captured until the next step?
No. > What happens at the final time step? Your function should still get called. > > 2. The projection is nonlinear, requiring the use of a SNES. I had > originally thought that I would create/configure/destroy the SNES within the > main routine of the code, and pass this to the PostStep through a user data > structure. However, the TSSetPostStep function seems to only take functions > which are exclusively functions of the TS. Likewise, I would need to create > a residual vector, r, for the SNESSetFunction. Is there a way to pass these > data structures, so that they can be reused. or would they have to be > created/destroyed within the PostStep function at each iterate? How costly > would that be? After you create the SNES and the TS call PetscObjectCompose() to attach the SNES to the TS then inside your post-step you can use PetscObjectQuery() or if you want to pass in more than a SNES use PetscContainerCreate(). > > > -gideon >
