[petsc-users] SNES and TS

Matthew Knepley knepley at gmail.com
Sun Jul 21 13:37:45 CDT 2013

On Sun, Jul 21, 2013 at 10:28 AM, Zou (Non-US), Ling <ling.zou at inl.gov>wrote:

> Dear All,
> I've been playing with TS with my transient problem. It so far works
> fine and I was able to deal with forward Euler and backward Euler time
> integration scheme very easy pretty much without changing anything in
> my code.
> I understand that TS works fine when the non-linear equations look like:
> du/dt = f
> dv/dt = g
> However, I currently have a non-linear equation system like
> h(du/dt, dv/dt) = f
> k(du/dt, dv/dt) = g
> both h and k are nonlinear function of du/dt and dv/dt. I wonder for
> this kind of situation, is TS still the best option for time

Yes, the implicit interface (IFunction and IJacobian) are the right way to
address this.
TS ex22 is an example that uses this interface, even though it is linear in
the derivatives.


> integration. For my understanding, I can solve the transient system
> using SNES directly like:
> h(du/dt, dv/dt) - f = 0
> k(du/dt, dv/dt) - g = 0
> and handle the time integration manually as it also would give me
> flexibility to use my own time integration schemes.
> I'd appreciate it if anyone could give some suggestions, and examples
> if possible (I love examples :)
> Best,
> Ling

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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