Kish, Mikael reminded me that I missed an important point you raised:
Yes, it is necessary to post the end=start+dur constraints if all three are
variables. The unary/cumulative constraints will not enforce these constraints
at all, so you can get incorrect solutions.
Cheers,
Guido
On 17 May 2011, at 18:29, Kish Shen wrote:
> Hi,
>
> In most versions of Gecode's cumulative and unary constraints, you need to
> provide the start, duration and end times for tasks. For the ECLiPSe
> cumulative and unary constraints, you only need to provide the start and
> duration times. I understand that having the end times for task allows for
> more opportunities for propagation, but are they needed (or more precisely,
> are the extra constraints end = start + duration needed). if the end times
> are not used anywhere.
>
> The reason I am asking is that in the ECLiPSe interface to Gecode, one of the
> aim is to provide compatibility to existing ECLiPSe code, so this means
> providing cumulative/unary constraints with flexible durations, but without
> end times, which is what ECLiPSe has. For these constraints, the user would
> have no access to the end times, but currently I still post the extra
> constraints end = start + duration for each task, as the Gecode call requires
> the end times, and MPG suggest that these constraints should be posted. But
> when I was looking at the code yesterday, I started to wonder if this makes
> sense if the user cannot see (and so cannot post constraints that will
> affect) the end times. So my question is, does it make sense to post these
> constraints under these conditions?
>
> Thanks and cheers,
>
> Kish
>
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Guido Tack, http://people.cs.kuleuven.be/~guido.tack/
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