Hi,
Uncle! I yield.
> That aside (depth-first search can be tweaked to work with conflict
> tracking etc), another problem is that your suggestion produces arguably
> suboptimal results when a higher-priority package requires a
> lower-priority one, because the locally optimal choice leads to a
> globally worse result. Here's a simple example:
>
> A has priority 500
> B has priority 500
> C has priority 400
> D has priority 1
>
> A depends on B | C
> B depends on D
>
> Should installing A pull in B (priority 500) and D (priority 1), or
> should it pull in just C (priority 400)? Your rule would produce the
> first result, but I think the second one is better.
I see what you're talking about. I agree the 2nd is better as well.
For my
preferences file "D" would be coming from Ubuntu or Debian Multimedia and I
would rather it come from Debian (Official).
> I stated things the way I did because it's a description of the
> desired result rather than the details of how it's achieved, which means
> we can discuss the important stuff without getting into stuff that's
> only important inasmuch as the result has to be achievable. Here's an
> example of what I meant: if you have two possible solutions to a
> dependency problem, and one contains only packages of priority 500 or
> greater, and another contains a package of priority 1, the priority-500
> solution will be produced first. [0] Right now aptitude is not capable
> of providing any "hard" guarantees about solution ordering, so even to
> the extent that it does try to order solutions, that ordering could be
> violated at any time.
>
> The next release will be able to provide some hard guarantees under
> technical conditions that I won't bore you with unless you're
> interested. :-)
Ummm.... I think I'll be able to just wait to try the next release of
aptitude. :)
>
> Daniel
>
> [0] there are some other constraints on solution order that I want to
> impose; this is probably the "last step" in the ordering, after
> solutions are otherwise equal.
Yep, even aptitude as-is plus this final tweak step would be a nice
improvement. This is probably the level I'm "being surprised" by aptitude's
results currently anyway.
Thanks for your work!
C.
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