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 subthresholdseeking 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.