This method is a shortcut to varLocalImpact(-1).

This method returns a variable evaluator. The evaluation is the impact of the variable computed at the current node of the search tree. This computation is made by probing on values from the domain of the variables. The parameter effort indicates how much effort sould be spent to compute this impact. When effort is equal to -1, every value of the domain is probed otherwise the nunber of probes effort will increase as the effort value increases.