A Note on the Convexity of Service-Level Measures of the (r, q) System
给出一个简单证明，说明在(r, q)库存系统中，平均未结订单和单位时间平均缺货量关于控制变量q和r是联合凸的。
This note gives a simple proof that in a (r, q) system the average outstanding backorders and the average stockouts per unit time are jointly convex in the two control variables q and r.