Network flows over time are a fascinating generalization of classical (static) network flows, introducing an element of time. They naturally model problems where travel and transmission are not instantaneous and flow may vary over time. Not surprisingly, flow over time problems turn out to be more challenging to solve than their static counterparts. In this survey, we mainly focus on the efficient computation of transshipments over time in networks with several source and sink nodes with given supplies and demands, which is arguably the most difficult flow over time problem that can still be solved in polynomial time.

翻译：随时间变化的网络流是经典（静态）网络流的一个引人入胜的推广，引入了时间要素。它们自然地模拟了传输和传播非瞬时完成且流量随时间变化的问题。毫不意外地，随时间流问题在求解上比其静态版本更具挑战性。本综述主要聚焦于具有多个源节点和汇节点（给定供应与需求）的网络中随时间转运的高效计算问题，这可以说是仍可在多项式时间内求解的最困难的随时间流问题。