Subthreshold-Seeking Behavior and Robust Local Search

Subthreshold-seeking behavior occurs when the majority of the points that an algorithm samples have an evaluation less than some target threshold. We characterize sets of functions where subthreshold-seeking behavior is possible. Analysis shows that subthreshold-seeking behavior, when possible, can be increased when higher bit precision is used with a bit climber search algorithm and a Gray code representation. However, higher precision also can reduce exploration. A simple modification to a bit-climber can improve its subthreshold-seeking behavior. Experiments show that this modification results in both improved search efficiency and effectiveness on common benchmark problems.