Focusing on the complexity of vendor selection problem in the face of uncertain situation and the random delay period which may be encountered in the procurement process,the method of continuous random variable discretion is applied to solve the combination of delay period of different suppliers as a combination of delay period of all suppliers so that the number of combinations can be reduced.Using convolution formula,the density function of sum of random variables which follow exponential distribution is proved with the same parameter and different parameters,and the delay costs under these situations are respectively estimated with the use of conditional expectation.Finally,the algorithm for the delay cost of all suppliers delay period under different conditions is given.%针对供应商选择问题中面临的不确定情况,以及采购过程中可能遇到随机延迟的现状,应用连续型随机变量离散化的方法,将不同供应商延迟周期的组合问题转化为所有供应商总的延迟周期的组合问题,从而减少了组合的数量.利用卷积公式证明了参数相同和参数互不相同两种情形下,m个服从指数分布的随机变量的求和密度函数,并且利用条件期望估计了每种情景下的延迟成本.最后,给出了所有供应商总延迟周期在不同情形下的延迟成本的算法。
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