说明：   学校超市选址问题（带权有向图的中心点） 设计要求：对于某一学校超市，其他各单位到其的距离不同，同时各单位人员去超市的频度也不同。请为超市选址，要求实现总体最优
(School Supermarket location problem (with the right of the center of a directed graph) design requirements: For a school supermarkets and other units to its distance from the different units at the same time the frequency of personnel to the supermarket is also different. Please supermarket location, required to achieve the overall optimum)