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

Emil Constantinescu emconsta at mcs.anl.gov
Mon Mar 23 20:08:22 CDT 2015

On 3/23/15 5:34 PM, Jed Brown wrote:
> Lisandro Dalcin <dalcinl at gmail.com> writes:
>> On 21 March 2015 at 17:32, Emil Constantinescu <emconsta at mcs.anl.gov> wrote:
>>> When -ts_theta_adapt is used, then it detects the instability as an error
>>> and reduces the step by a lot! wlte=1.24e+03 which means that the reduction
>>> should be severe but the controller tries 0.1*dt and that seems to pass but
>>> it "jig-saws" (take a look at the next attempted step), which means that it
>>> is likely unstable.
>> I think -ts_theta_adapt is seriously broken, I cannot make sense of
>> the way the error estimator is computed.
> This was Shri's implementation.  TSEvaluateStep_Theta looks wrong to me,
> both using U as an input and assuming that Xdot is set.  I don't even
> know what the intended math is for a first-order embedded estimate in
> midpoint (theta=0.5).

I was off for the last few days and I wasn't able to follow the call 
sequence - I had assumed it was correct. I'll take Debo and look into it.


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