[gecode-users] about the backtrack

[Guido Tack]

Juan Carlos wrote:
> In order to find the best solution of  a problem that I'm working  
> on, I have to branch over an IntVarArray , so  I have created a  
> custom branch with an heuristic. (like in the black hole or queens  
> example).  And use the BAB engine.
>
> This  branching works fine, but it could be improved if the vars  
> that should be unassingned after  a basic solution is found are  
> selected in a different way. I mean like a custom backtrack with a  
> function that selects the best var to be reassigned.

Backtracking in Gecode is based on copying and recomputation, and  
therefore does not "unassign" any variables.  When you backtrack, you  
restore a previous state in the search tree (for example that of the  
parent of the current search node), and then commit to another of its  
remaining alternatives.  The only way to determine where search  
proceeds is therefore in the branching.

Maybe, if you explain in a little more detail how you would like the  
search to behave, we can help you cast that idea into your custom  
branching.

Cheers,
	Guido