[petsc-dev] DMGetNamedGlobalVector() implementation?

[Jed Brown]

On this topic, we should become much more adamant, at least in
documentation and maybe also in naming about which arguments are scale-free
and which are scale-dependent. Internally, we (Peter and I) have a system
that is being followed carefully, including in the examples that we write.
Things compose well when these unwritten guidelines are followed.

On Thu, Jul 19, 2012 at 1:25 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Thu, Jul 19, 2012 at 1:19 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>>   Why not implement it using PetscObjectQuery()/PetscObjectCompose()? and
>> not have to introduce a whole new datatype DMNamedVecLink linked list and
>> other crap?
>>
>
> The only reason this thing has to exist, and it really has to exist in
> some form, is that we have a reference loop. For example, the SNES Vec X is
> obtained from the DM (thus X references the DM), but must be made available
> to the KSP callback that uses the DM. If we attached X to the DM, then we
> would have a loop X -> DM -> X. Same for the TS vector needed in
> SNESComputeFunction.
>
> The general form of PetscObjectCompose allowing reference loops is
> terribly dangerous and imprecise (you end up implementing a sort of limited
> garbage collector that periodically looks for loops, but that is super
> dangerous in parallel because you need determinism in destruction).
>
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