[petsc-dev] TS Terminology

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Sat, Oct 21, 2017 at 9:28 AM, Jed Brown <jed at jedbrown.org> wrote:
>
>> Matthew Knepley <knepley at gmail.com> writes:
>>
>> > On Fri, Oct 20, 2017 at 4:21 PM, Jed Brown <jed at jedbrown.org> wrote:
>> >
>> >> Matthew Knepley <knepley at gmail.com> writes:
>> >>
>> >> >> Note that TSComputeIFunction is very much like SNESComputeFunction,
>> >> >> which includes
>> >> >>
>> >> >>   if (snes->vec_rhs) {
>> >> >>     ierr = VecAXPY(y,-1.0,snes->vec_rhs);CHKERRQ(ierr);
>> >> >>   }
>> >> >>
>> >> >> Why haven't you complained about that?
>> >> >>
>> >> >
>> >> > Good point. I did not notice. This came up because the initialization
>> >> > of input vectors is inconsistent between TSComputeIFunction() and
>> >> > TSComputeIFunctionLocal(). The former does not zero the output vec,
>> >> > but the later does.
>> >>
>> >> The latter function doesn't exist so maybe you mean
>> >> TSComputeIFunction_DMDA with ADD_VALUES?  That's because the DMDA needs
>> >> it when using ADD_VALUES, just like SNESComputeFunction_DMDA.  When
>> >> using INSERT_VALUES, the user is responsible for setting every entry.
>> >> Is any of this different from SNES?
>> >>
>> >
>> > No I mean TSComputeIFunction_DMLocal().
>>
>> That's just some code you wrote for finite elements when you hard-coded
>> it for ADD_VALUES.
>>
>>   ierr = DMLocalToGlobalBegin(dm, locF, ADD_VALUES, F);CHKERRQ(ierr);
>>   ierr = DMLocalToGlobalEnd(dm, locF, ADD_VALUES, F);CHKERRQ(ierr);
>>
>> It's analogous to what TSComputeIFunction_DMDA does when you set
>> ADD_VALUES.  Note that with INSERT_VALUES, as is typically used for FD
>> and FV, you can assemble directly into the global vector
>>
>> > So if you use DMTSSetIFunction() you get different initialization
>> > behavior than if you use DMTSSetIFunctionLocal().  This is what Brad
>> > was complaining about originally.
>>
>> Maybe you should document your finite element interfaces better.
>>
>
> I think the fair statement would be that it is not documented either way.

Yes, it's EXACTLY the same as how SNESComputeFunction does not zero the
vector, but SNESComputeFunction_DMLocal does because it's a finite
element/ADD_VALUES interface.  You could start by documenting that.