[petsc-users] Turning off TSADAPT still adapts time step

[Barry Smith]

  Run in the debugger (with one process obviously) to see why it is still calling an adaptor.

  Barry

> On Apr 24, 2015, at 3:16 PM, Mark Lohry <mlohry at princeton.edu> wrote:
> 
> Trying a simple stiff test case (y'=y^2*(1-y)) using TSBEULER, to get a feel for implicit stepping with JFNK.
> 
> I'm giving it a pretty large timestep, and the default appears to start adapting the time step around the stiff part of the solution. So I tried turning it off:
> 
>  TSAdapt adapt;
>  TSGetAdapt(its,&adapt);
>  TSAdaptSetType(adapt,TSADAPTNONE);
> 
> and even fixing the limits:
> 
>  TSAdaptSetStepLimits(adapt,40.0,40.0);
> 
> And it still ignores it and adapts anyway. At t=800 (where the solution gets very stiff, so one would normally see adaptive stepping there if it was desired) it's dropping dt from 40 to 10.
> 
> Printing (t,y) here from the ts monitor:
> 
> 600.000000,0.002790;
> 640.000000,0.003198;
> 680.000000,0.003761;
> 720.000000,0.004606;
> 760.000000,0.006072;
> 800.000000,0.010155;
> 810.000000,0.011452;
> 820.000000,0.013161;
> 830.000000,0.015538;
> 840.000000,0.019126;
> 850.000000,0.025426;
> 860.000000,0.043639;
> 900.000000,0.975519;
> 940.000000,0.999402;
> 980.000000,0.999985;
> 1020.000000,1.000000;
> 1060.000000,1.000000;
> 1100.000000,1.000000;
> 1140.000000,1.000000;
> 1180.000000,1.000000;
> 
> Any idea? Adaptive stepping is great, but I'd still like to be able to fix the time step.
> 
> 
>