[gecode-users] Arc consistency, value and variable ordering

[Guido Tack]

The choice is made dynamically at each choicepoint, depending on the current domains.  So in your REGRET example, X would be chosen over Y because it has a smaller min-regret.  INT_VAR_ SIZE_AFC_MIN is not first-fail, it's "dom/weighted degree", see the tutorial documentation, Section 9.1.  First-fail would be INT_VAR_SIZE_MIN.
There's no (variable, constraint) pairs in Gecode, as Christian pointed out Gecode is not an AC algorithm.  INT_VAR_NONE simply picks, at each choicepoint, the first unassigned variable from the array.
There is no additional documentation except the tutorial and the reference docs you mentioned.  Just experiment with different strategies using Gist, you will see what choices they make.

Cheers,
	Guido

Claudio Cesar de Sá wrote:

> Hi,
> 
> In arc consistency algorithms, such the AC3 and its derivatives,  you need do two choices:
> 
> 1: Which is order of these variables are to be considered?
> 2. Which is the order of their  values are assigned to the variable?
> 
> These two parameters are in branch method, section 9.1., figure 9.1 ...
> I am with some doubts on their meanings, such:
> [INT\_VAR\_REGRET\_MIN\_MIN:]     With smallest min-regret.
> The min-regret of a variable is the difference between the smallest and second-smallest value still in the domain.
> 
> For example: considering  variables X and Y ... Dom(X)={2, 5, 8, 11}    and  Dom(Y)={1, 6, 18,  20}  .... X should be chosen
> once |2 - 5|  has a small  regret ... comparing with |1 - 6| of Y ?
> 
> Other question, the parameter  INT\_VAR\_SIZE\_AFC\_MIN,  should the  well-known as first-fail?
> 
> Or INT\_VAR\_NONE,  first unassigned, should be the first variable found in the list of pair (variable, constraint) considered
> in arcs consistency algorithms?
> 
> Where can I find details of these parameters accept by the Gecode? In int.hh are their specification
> 
> 
> 
> 
> 
> 
> -- 
> claudio 
> 
> 
> 
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-- 
Guido Tack, http://people.cs.kuleuven.be/~guido.tack/




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