[gecode-users] task end times in cululative/unary constraints

[Kish Shen]

Hi Guido,

Do you mean that in my specific situation, where the user only sees the 
start and duration times, that these might be given incorrect values, or 
is it only the end times that might be given incorrect values? [I guess 
this boils down to if you use both start and end times to check for 
overlapping of tasks, rather than start and duration]

Thanks and cheers,

Kish

On 23/05/2011 14:16, Guido Tack wrote:
> 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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