[gecode-users] Value selection when branching

[Lars Otten]

Hi,

On 02/07/06 15:38, Guido Tack wrote:
>> I still haven't solved the previous problem (about the strange propagation
>> behaviour), but since for the moment there is a workaround, I have started
>> to work on some other things at the same time, one of them random value
>> selection when branching.
> 
> Uh, I tried that too and failed miserably ;-)

That does not sound promising... :-/

> To understand this behaviour, you have to understand how the search engine 
> works. One severe problem is recomputation: this requires that the branching 
> is deterministic, i.e. for equivalent spaces it must always result in the 
> same choice. This is clearly not the case here. You could switch off 
> recomputation by giving -c_d 1 -a_d 1 as command line parameters. Please try 
> out if that changes anything.

Nope, doesn't help. Thanks nevertheless.

> It might still not work, because even if you never recompute spaces, you are 
> not guaranteed that for one space at one point in the search tree the 
> branching is evaluated only once. The only way out of this trap is to use 
> something that will be completely deterministic, so that for equivalent 
> spaces you will always get the same choice.

Well, the whole point here is (pseudo-)nondeterminism. ;-)
I will have to think about the problem a little bit and see what I can come
up with.

/Lars