[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 <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.
>>
>>
>>