[petsc-users] projection methods in TS

[Gideon Simpson]

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 <knepley at gmail.com> 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 <bsmith at mcs.anl.gov <mailto:bsmith at mcs.anl.gov>> 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 <gideon.simpson at gmail.com <mailto:gideon.simpson at gmail.com>> 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

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