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

[Mark Lohry]

I'm new to PETSc and not sure how to go about debugging. Running with 
-start_in_debugger runs in gdb with the normal output (where would i put 
a breakpoint for this?) and running with -info dumps a lot of 
information but only related to SNES and KSP, nothing about time 
stepping or adapt.


On 04/24/2015 04:29 PM, Barry Smith wrote:
   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 <mlo...@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.