> Now I see, I was confused about how the backtrack works. > > The idea is a Local Search Method, first find a basic solution, and then > make little changes till the best solution is found, here are the steps: > > 1)choose the best value for each variable (this value is selected by a > function based on external information), once all the variables had been > assigned thats a basic solution. > 2) Based on that solution , re-assign some variables in order to find a > better solution in a fast way. The variables that are going to be > re-inserted are chosen by a function based on external information and the > value is chosen by the same function of step 1. > 3) repeat 2 till no solution left. > > By external information I mean the information of the problem instance. > > Now I have some ideas about how to implement this local search but they are > not clear yet. Any suggestions are welcome. > > Thank you. > > Juan Carlos > > > On Wed, Jun 18, 2008 at 2:05 AM, Guido Tack <[EMAIL PROTECTED]> wrote: > >> 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 >> >> >
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