“…Until recently it has been been easy to adapt plans derived from these models to more realistic conditions (see [21], [22]). The approaches tend to fall into three categories, complete search based upon mixed-integer program (MIP) formulations [21], [23], locally optimal search such as constructive heuristics [14], [15], and meta-heuristics [24], [25], [26], [27], [28], [29].…”