[petsc-dev] Discussion about time-dependent optimization moved from PR

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:

>> I don't see how any of the present interfaces work for waveform
>> relaxation.  I also think that is rarely a desirable technique -- too
>> many awkward limitations.  My recollection is that Borzi only uses it
>> for parabolic problems, for which adaptivity would have given much
>> faster/cheaper solutions of equivalent accuracy.  The techniques are
>> theoretically interesting, but have not demonstrated sufficient
>> practicality to worry about.  Someone doing research on these full-space
>> methods can just discretize space-time using SNES.
>
>    Yes, but since that is a huge involved process (they need to manage
>    time discretization etc themselves) they will NEVER compare with
>    reduced methods and that is a huge part of the problem. 

Waveform relaxation and related methods intimately couples the temporal
discretization with the spatial discretization.  It's a "transposed"
interface.

>    People do "research" in one or the other approach and never compare
>    the two, leading to bad research. If we can combine them then one
>    can actually compare the two approaches.
>
>    Barry
>
> I'm not saying it is possible to have a nice API that combines them.

If we don't know how to combine them in a nice API and one is very
important/practical while the other is research of questionable
practicality, I'd rather focus on making the important thing work well
rather than constantly hedging to possibly include the questionable
thing.