A comparison of average and discounted cost models for the dynamic lot size inventory problem

It is a common practice in the inventory literature to use average cost models as approximations to the theoretically correct discounted cost models. An average cost model minimizes the average undiscounted cost per period, while a discounted cost model minimizes the total discounted cost over the problem horizon. This paper attempts to answer an important question: How good are the results (the total discounted costs) for the average cost models compared to those for the discounted cost models? This question has been conclusively answered for the simplest inventory model where the demand rate and other parameters are assumed to remain constant in time. This paper addresses this issue for the first time for the case where demand rates are allowed to be nonstationary in time.A discounted cost model has been developed in the paper to carry out this comparison. It is shown that a simple dynamic programming algorithm can be used to find optimal order policies for the discounted cost model.The effect of the varying interest rates and other parameters on the relative performance of the average cost model has been studied by developing an insightful analysis and also by doing a computational study. The results show that, while the average cost model can cost as much as about 26% more than the discounted cost model in extreme cases, this increase is not significant for the parameter values in the range of the common interest.     

信息成本、博弈规则与经济效率:兼议国有资产运营的制度选择

本文假设委托人或监督人能够以一定成本收集信息从而能依一定概率观察到影响委托人报酬的生产力水平 ,研究了存在信息传递成本的多委托人模型、零信息传递成本的多委托人模型和委托人 -监督人 -代理人模型 ,比较了不同的博弈规则或制度安排在均衡状态下的信息分布与经济体效率 .本文的研究结论表明 ,给定委托人或监督人的信息成本与信息处理能力 ,博弈规则是决定信息分布与经济体效率的关键因素 .存在信息传递成本时 ,由于坐便车行为 ,信息分布的不对称程度最为严重 ,也具有最低的效率 .零信息传递成本的多委托人模型中 ,信息不对称程度最弱 ,并且在很弱的条件下具有最高的效率 .委托人 -监督人 -代理人模型中 ,仅当监督人具有充分低的信息收集成本和充分高的信息处理能力时 ,才有可能具有较高的效率 .就本文的模型所支持的结论而言 ,国有企业的公司制改造 ,并降低资本市场传递与处理信息的成本 ,是更富于效率的一种制度安排 .相反 ,由于作为监督者的国有资产管理部门并不佣有产权 ,它没有足够的动机去认真履行监督职责 ,同时 ,诱导监督者其不与代理人串通作弊的成本之高昂 ,都将进一步降低这种制度安排下国有资产运营的效率 .     

Measuring efficiency at U.S. banks: Accounting for heterogeneity is important

Estimates of bank cost efficiency can be biased if bank heterogeneity is ignored. I compare X-inefficiency derived from a model constraining the cost frontier to be the same for all banks in the U.S. and a model allowing for different frontiers and error terms across Federal Reserve Districts. I find that the data reject the single cost function model; X-inefficiency measures based on the single cost function model are, on average, higher than those based on the separate cost functions model; the distributions of the one-sided error terms are wider for the single cost function model than for the separate cost functions model; and the ranking of Districts by the level of X-inefficiency differs in the two models. The results suggest it is important when studying X-inefficiency to account for differences across the markets in which banks are operating and that since X-inefficiency is, by construction, a residual, it will be particulary sensitive to omissions in the basic model.     

带有交易费用和持有成本的局内采购管理模型竞争分析

采购管理是企业经营活动的一个重要组成部分,更加有效的采购管理策略可以大大减少采购费用,对于企业的经营业绩非常重要。在现实的经济活动中交易费用和持有成本在企业管理费用中占很大一部分比率,而采购过程影响着交易费用和持有成本。所以在前人研究的基础上,将交易费用和持有成本引入到局内采购管理模型中,使得运用该策略无论以后采购价格如何变化,局内人的采购成本总是对应局外问题最优采购成本的一定比例c之内,并得到c与原模型相同。但是引入交易费用和持有成本后每天的采购量将发生变化,原模型是在不考虑交易费用和持有成本的前提下得得到的每天采购量和最优竞争比,如果考虑到现实经济活动中不可忽略的交易费用和持有成本,仍然按照原模型来确定每天的采购量来采购就不能得到最优竞争比c。所以本文考虑到了交易费用和持有成本,并得到和原模型不同的每天采购量,并求出最优竞争比c。     

贫信息背景下朱兰质量成本灰色GM(1,1)测算模型

朱兰曲线将质量总成本表示为质量投入与直接质量损失的合成.针对不同质量水平下的质量成本变化趋势,建立保证成本和故障成本的正负指数模型来确定最佳质量成本.灰色均值GM(1,1)测算模型可以同时克服"少数据""贫信息"的缺陷,更加精确地拟合质量成本的变动趋势.与指数函数模型模拟效果进行对比,结果表明灰色系统理论系列模型具有较高的预测精度,将指数函数模型和灰色GM(1,1)模型结合起来可以为企业提高质量管理水平尤其是质量成本管理提供依据和指导.     

Designing a new computational approach of partial backlogging on the economic production quantity model for deteriorating items with non-linear holding cost under inflationary conditions

This paper discusses the production inventory model over an infinite time horizon. Here we consider demand as a function of stock and time. Deterioration is a function of time and time-varying production. Our objective is to minimize the total cost which is a function of set up cost, holding cost, shortage cost, and opportunity cost due to lost sales. The traditional costs such as purchasing cost, shortage cost and opportunity cost due to lost sales are kept constant. We consider holding cost to be a non-linear function of time. Shortages are allowed and are partially backlogged. Here, time durations are the decision variables. Numerical examples are given to illustrate the model.     

Capacitated location model with online demand pooling in a multi-channel supply chain

This paper presents a location model that assigns online demands to the capacitated regional warehouses currently serving in-store demands in a multi-channel supply chain. The model explicitly considers the trade-off between the risk pooling effect and the transportation cost in a two-echelon inventory/logistics system. Keeping the delivery network of the in-store demands unchanged, the model aims to minimize the transportation cost, inventory cost, and fixed handling cost in the system when assigning the online demands. We formulate the assignment problem as a non-linear integer programming model. Lagrangian relaxation based procedures are proposed to solve the model, both the general case and an important special case. Numerical experiments show the efficiency of our algorithms. Furthermore, we find that because of the pooling effect the variance of in-store demands currently served by a warehouse is an important parameter of the warehouse when it is considered as a candidate for supplying online demands. Highly uncertain in-store demands, as well as low transportation cost per unit, can make a warehouse appealing. We illustrate with numerical examples the trade-off between the pooling effect and the transportation cost in the assignment problem. We also evaluate the cost savings between the policy derived from the model, which integrates the transportation cost with the pooling effect, and the commonly used policy, which is based only on the transportation cost. Results show that the derived policy can reduce 1.5–7.5% cost in average and in many instances the percentage of cost savings is more than 10%.     

An analytical method for cost analysis in multi-stage supply chains: A stochastic network model approach

This paper studies the cost distribution characteristics in multi-stage supply chain networks. Based on the graphical evaluation and review technique, we propose a novel stochastic network mathematical model for cost distribution analysis in multi-stage supply chain networks. Further, to investigate the effects of cost components, including the procurement costs, inventory costs, shortage costs, production costs and transportation costs of supply chain members, on the total supply chain operation cost, we propose the concept of cost sensitivity and provide corresponding algorithms based on the proposed stochastic network model. Then the model is extended to analyze the cost performance of supply chain robustness under different order compensation ability scenarios and the corresponding algorithms are developed. Simulation experiment shows the effectiveness and flexibility of the proposed model, and also promotes a better understanding of the model approach and its managerial implications in cost management of supply chains.     

Reliability and cost analysis of series system models using fuzzy parametric geometric programming

In this paper, we have discussed series system models with system reliability and cost. We have considered two types of the model; the former focuses on a problem of optimal reliability for series system with cost constraint and the latter is a center system cost model with reliability goal. It is necessary to improve the reliability of the system under limited available cost of system and also to minimize the systems cost subject to target goal of the reliability. Practically, cost of components has always been imprecise with vague in nature. So they are taken as fuzzy in nature and the reliability models are formulated as a fuzzy parametric geometric programming problem. Numerical examples are given to illustrate the model through fuzzy parametric geometric programming technique.     

多阶段生产系统最优生产批量和原材料订购决策模型

Sarker和Parija(1996)建立了生产系统最优生产批量和原材料订购决策模型。然而他们的模型仅局限于单阶段生产系统,本文将他们的模型扩展到多阶段生产系统,我们首先建立了使整个多阶段生产系统总成本最小的各阶段最优生产批量、原材料订购批量及阶段之间的运输批量模型,然后分析了原材料订购费、半成品运费及设备安装费的敏感性。最后,我们结合实例综合分析了原材料订购费、半成品运输费和设备安装费的变化及最小值点取整后对原材料订购决策、最优生产批量和总成本的影响。     

提前期不确定条件下的预防性维修备件存储模型研究

在考虑预防性维修周期和提前期不确定的条件下,分别研究备件存储与其相关的维修费用、缺货费用、库存费用以及订购费用等四种费用之间的关系,明确了备件存储量对各项费用的影响.以各项费用总和最小化为目标,构建了提前期不确定条件下的预防性维修备件存储模型.通过备件存储模型的构建,对备件存储过程中的各项成本进行分析,以期对备件库存策略的确定给出一种解决方案.     

A probabilistic programming model for blending aggregates

The paper introduces the formulation of a probabilistic programming model to find the optimum mix proportion of aggregates to meet the specific grading requirement in order to minimize the cost which consists of the material cost and the expected penalty cost. The model is probabilistic since the gradation, which is the major parameter, is a random variable. A linear programming model is first formulated. Using the LP solution as initial value, a direct search technique is then employed to solve the problem. The model is expected to be applicable to any problem of aggregates blending. In this paper, however, the mixing aggregates of an asphalt mixing plant is exemplified to test the applicability of the model.     

基于独立分量分析——最小二乘支持向量机的公路建设项目投资估算新模型

为快速、准确地进行公路建设项目投资估算,提出了一种新型的公路建设项目投资估算模型.该模型首先基于独立分量分析技术,根据最小互信息原理,有效分离出公路建设项目投资估算的独立影响因素源.然后,将这些独立影响因素源用于最小二乘支持向量机的训练,从而建立了基于独立分量分析技术—最小二乘支持向量机的公路建设项目投资估算模型.该模型将独立分量分析技术的盲信号分离能力与最小二乘支持向量机处理有限样本条件下非线性回归问题的优势有机结合,提高了模型预测的准确性.     

模糊用户需求约束下再使用产品质量改进设计

大多数停用的产品需要按照用户需求进行质量改进后再使用,针对用户对用户属性的要求改进率具有一定的模糊性的问题,应用模糊理论和质量功能配置的方法,以质量改进成本最低为目标建立了质量改进设计的模糊数学规划模型,模糊优化结果即兼顾了用户需求改进约束的满足程度,又考虑了质量改进成本最小,水泵再使用案例表明该方法能帮助质量改进人员规划出模糊用户需求约束下质量改进成本较低的设计方案.     

Cost of ownership model for spare engines purchase for the Korean navy acquisition program

Major weapon system acquisition programmes often require high initial purchase cost which can be a burden for the procurement of a highly reliable system. In order to avoid the tendency of acquiring a less expensive weapon system with lower performance, a cost of ownership (COO) model can be applied to assess the lifetime cost of the weapon system. In many existing cost estimation models for weapon systems, the failure rate of the system is assumed to be constant and the functional relationship between the initial purchase cost and maintenance cost is not well defined. In this paper, we propose a revised COO model where random effects models are employed to accommodate the variations of the system failure frequency and repair time. It is expected that our model can contribute to the cost-effective procurement of spare engines for the Korean Navy acquisition programme within the limited national defence budget.     

Optimal age-replacement model with age-dependent type of failure and random lead time based on a cumulative repair-cost limit policy

In this paper, we consider an age-replacement model with minimal repair based on a cumulative repair cost limit and random lead time for replacement delivery. A cumulative repair cost limit policy uses information about a system’s entire repair cost history to decide whether the system is repaired or replaced; a random lead time models delay in delivery of a replacement once it is ordered. A general cost model is developed for the average cost per unit time based on the stochastic behavior of the assumed system, reflecting the costs of both storing a spare and of system downtime. The optimal age for preventive replacement minimizing that cost rate is derived, its existence and uniqueness is shown, and structural properties are presented. Various special cases are included, and a numerical example is given for illustration. Because the framework and analysis are general, the proposed model extends several existing results.     

Single Supplier�CBuyer Integrated Inventory Model Under Multiple JIT Delivery and Stock-Dependent Demand

In this paper, an integrated inventory model for a supply chain comprising of single buyer and single supplier is studied when demand is stock-dependent and units in inventory deteriorate at a constant rate. The total cost of the integrated system consists of the transportation cost, inspection cost and the cost of less flexibility under the assumption of JIT deliveries. The total integrated cost of single-supplier and single-buyer is minimized with respect to number of inspections and deliveries, the cycle time of deliveries and the delivery size for the replenishment time. A numerical example is given to validate the model. The sensitivity analysis carried out suggests that the unit inspection cost, deterioration rate of units in inventory and stock-dependent parameter are the critical factors.     

考虑商品数量和商品拣选成本的AGV智能仓库订单分批问题研究

AGV(Automated Guided Vehicle,自动导引车)智能仓库是一种基于“货到人”拣选模式的自动化仓库。本文考虑了订单中商品的需求量和货架上商品的存储量,以极小化货架搬运成本和商品拣选成本为目标,建立了AGV智能仓库订单分批问题的整数规划模型。本文针对订单分批问题的特点,提出了一种基于订单和货架交替选择的贪婪求解算法。对比CPLEX求解器的精确最优解,本文提出的贪婪算法的误差百分比不超过10%,平均误差百分比为5.38%;对比基于相似性的分批算法的求解结果,本文提出的贪婪算法不仅运算时间更短,解的质量也更好。进一步地,对比不考虑商品拣选成本的订单分批模型,本文提出的模型在不明显增加货架搬运成本的前提下,可以大幅度降低商品拣选成本。因此,在订单分批模型中考虑商品拣选成本是非常必要的。     

Integrated vendor–buyer cooperative inventory models with controllable lead time and ordering cost reduction

This study deals with the lead time and ordering cost reduction problem in the single-vendor single-buyer integrated inventory model. We consider that buyer lead time can be shortened at an extra crashing cost which depends on the lead time length to be reduced and the ordering lot size. Additionally, buyer ordering cost can be reduced through further investment. Two models are presented in this study. The first model assumes that the ordering cost reduction has no relation to lead time crashing. The second model assumes that the lead time and ordering cost reduction are interacted. An iterative procedure is developed to find the optimal solution and numerical examples are presented to illustrate the results of the proposed models.     

An EOQ Model for Deteriorating Items with Time Varying Demand and Costs

A generalized EOQ model for deteriorating items is considered here in which the demand rate, deterioration rate, holding cost and ordering cost are all assumed to be continuous functions of time. Shortages are also allowed and are completely backlogged. The planning horizon is finite and the replenishment periods are assumed to be constant. The optimal replenishment policy and the decision rule which minimizes the total system cost are derived. A numerical example is given to illustrate the developed model. Sensitivity analysis is also presented for the given model.