[petsc-users] TimeStepper norm problems. EMIL Please read this

[Lisandro Dalcin]

On 24 March 2015 at 06:15, Emil Constantinescu <emconsta at mcs.anl.gov> wrote:
> On 3/23/15 4:44 AM, Lisandro Dalcin wrote:
>
> Lisandro, that's a neat idea. If you are basically moving in the multistep
> realm for error estimation with one-step methods,

I'm wondering if no one ever did it. I could not find any reference.

> I think there are two
> considerations:
>
> 1. The equations need to be continuous (no restarting, no events) or they
> would have to reset the error estimator somehow.
>

Indeed. My generalized-alpha code does not handle events at all. I'll
take a look into this. About restarting (not sure if we are talking
about the same thing), I have some code that is specific to
generalized-alpha (In the initial time step, I solve twice with
backward-Euler using dt/2 and dt) that let me properly initialize
generalized-alpha and also compute an initial error estimator.

> 2. Backward differences are sensitive to time stepping changes; unlike
> one-step methods that can accommodate any step changes, B-D has strict
> limits for stability. While this does not play a crucial role (it is just
> the estimator);

Of course, though my B-D is order 2, and as you said, it is the just
for the estimator.

> if the time step varies wildly (can be easily constrained),
> it may create some problems with the estimator.
>

Indeed, the default clipping 0.1,10 is usually too wide, I usually do
-ts_adapt_basic_clip 0.5,2.0

Emil, is there any chance you can try my code with your problem? I
really need some feedback to push this to PETSc, otherwise

-- 
Lisandro Dalcin
============
Research Scientist
Computer, Electrical and Mathematical Sciences & Engineering (CEMSE)
Numerical Porous Media Center (NumPor)
King Abdullah University of Science and Technology (KAUST)
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