Re: CLP(FD): what is necessary?

A.L. wrote:
On Thu, 13 Mar 2008 17:50:54 +0000, Joachim Schimpf
<jschimpf@xxxxxxxxx> wrote:
Having propagators wake up with different priority can be
quite important, so i think it is an important feature for
a constraint system. Probably it is more relevant for a
system like ECLiPSe that aims at combining different solution
methods, than for a system that just wants to do FD.

OK, I am bot familiar with current version of ECLIPSE... Are
priorities defined for each constraint separately, or across teh
system?

It's a simple scheme of a small number (12) of priorities
across the system.


> And what happens if I am using 2 custom constraints, each with
its own priorities numbered from 1 to 5?...

We've had endless discussions about an improved priority scheme
within the ECLiPSe team and with users, but never arrived at a
satisfactory proposal. We considered float-priorities, partially
ordered ones, priority vectors, you name it...
There is some risk of trying to do things via priorities that are
better done via data-driven dependencies or localised computations.

The current, simple system allows you to assign priorities roughly
according to propagator complexity or effectiveness, to give debugging
and visualisation goals high priority, and a few other tricks.
A principle is that priority choice should not affect correctness,
only efficiency.


-- Joachim
.

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