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Vehicle routing decision support for a local retailer 本地零售商的车辆路线决策支持
Pub Date : 2021-06-01 DOI: 10.5784/37-1-691
J. V. Vuuren, Aaron Shuttleworth
One of the most challenging decisions that has to made routinely by dispatch managers at distribution centres of warehousing and distribution businesses in the retail sector involves the assignment of delivery vehicles to service customers exhibiting demand for retail goods and the subsequent routing of these delivery vehicles to the various customers and back again. Perhaps surprisingly, these dispatch managers do not always use vehicle routing software to schedule goods deliveries to customers, instead often relying on teams of human schedulers who perform this task manually. The reason for not using such software is usually a perception that it may be difficult to integrate the software with existing enterprise resource planning systems already in use. In such cases, estimates of potential costs savings that may be brought about by such software is often required before the dispatch department will risk the significant step towards investing in vehicle routing planning software. Dispatch managers may then employ these cost savings estimates in cost-benefit trade-off analyses. This paper contains a practical case study in which the potential cost savings of a vehicle routing optimisation approach are quantified for a large retail distribution centre in the South African Western Cape in a bid to support its decision as to whether or not to invest in vehicle routing planning software.
在零售行业的仓储和分销业务的配送中心,配送经理必须例行做出的最具挑战性的决定之一,涉及到将配送车辆分配给有零售商品需求的服务客户,以及随后将这些配送车辆分配给不同客户并再返回。也许令人惊讶的是,这些调度管理人员并不总是使用车辆路线软件来安排向客户交付货物的时间,而是经常依靠人工调度团队来手动执行这项任务。不使用此类软件的原因通常是认为将软件与已经在使用的现有企业资源规划系统集成可能很困难。在这种情况下,调度部门在冒险投资车辆路线规划软件之前,通常需要对这种软件可能带来的潜在成本节约进行估计。然后调度管理人员可以在成本效益权衡分析中使用这些成本节约估算。本文包含了一个实际的案例研究,其中车辆路线优化方法的潜在成本节约被量化为南非西开普省的一个大型零售配送中心,以支持其是否投资车辆路线规划软件的决定。
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引用次数: 1
Estimating net ideal cycle time for body-in-white production lines 估算白车身生产线的净理想周期时间
Pub Date : 2021-06-01 DOI: 10.5784/37-1-683
W. Grobler, D. Kotzé, J. Joubert
In the automotive industry, a Body in White (BIW) refers to the first step, the basic structure, in the production of a vehicle. Once a BIW production line has been built, the (maximum) capacity is fixed and throughput is therefore limited by the equipment specified during the design phase. The main metric used to inform the production line design is the Net Ideal Cycle Time (NICT). Unfortunately, the state of practice to estimate the NICT is a basic heuristic that does not account for production variation. In this paper, we challenge the current estimation approach by proposing an alternative that assumes actual production to follow a Weibull distribution. The proposed model is derived and estimated from empirical data. The results suggest that BIW production lines have traditionally been designed with too low a capacity, resulting in planned throughput rarely being achieved. On the other hand, increasing the design capacity implies a higher initial investment. In this paper it is demonstrated that the higher investment required is offset by reduced losses, resulting in more reliable planning and returns.
在汽车工业中,白车身(Body In White,简称BIW)指的是汽车生产的第一步,即基本结构。一旦白车身生产线建成,(最大)产能是固定的,因此产量受到设计阶段指定设备的限制。用于通知生产线设计的主要指标是净理想周期时间(NICT)。不幸的是,估计NICT的实践状态是一种基本的启发式方法,不能解释生产变化。在本文中,我们通过提出一种替代方法来挑战当前的估计方法,该方法假设实际生产遵循威布尔分布。所提出的模型是根据经验数据推导和估计的。结果表明,传统的白车身生产线设计的产能太低,导致计划的产量很少实现。另一方面,增加设计能力意味着更高的初始投资。本文证明了较高的投资需要被减少的损失所抵消,从而产生更可靠的规划和回报。
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引用次数: 1
An overview of survival analysis with an application in the credit risk environment 概述生存分析及其在信用风险环境中的应用
Pub Date : 2021-02-01 DOI: 10.5784/36-2-690
M. Smuts, J. Allison
Survival analysis has become a popular technique to more accurately model the probability of default in the credit risk environment with the ultimate goal of finding the optimal price for credit. In this paper we present an overview of some of the basic concepts of survival analysis. The focus is specifically on the Cox Proportional Hazards (CPH) model and the mixture cure model, which is a general alternative to the CPH model. A detailed algorithm that can be used to simulate survival times (default times) from a mixture cure model is provided. A parametric CPH and mixture cure model are fitted to a simulated data set and the benefits of fitting the latter model are illustrated.
生存分析已成为一种流行的技术,以更准确地模拟信用风险环境下的违约概率,最终目标是找到最优的信贷价格。在本文中,我们提出了一些生存分析的基本概念的概述。重点是考克斯比例风险(CPH)模型和混合固化模型,这是CPH模型的一般替代方案。提供了一种详细的算法,可用于模拟混合固化模型的生存时间(默认时间)。对模拟数据集拟合了参数化CPH和混合固化模型,并说明了拟合后一模型的好处。
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引用次数: 3
A machine learning approach for automated strip packing algorithm selection 一种基于机器学习的条带自动包装算法选择方法
Pub Date : 2021-02-01 DOI: 10.5784/36-2-686
Rosephine G. Rakotonirainy
This paper deals with strip packing metaheuristic algorithm selection using data mining techniques. Given a set of solved strip packing problem instances, the relationship between the instance characteristics and algorithm performance is learned and is used to predict the best algorithms to solve a new set of unseen problem instances. A framework capable of modelling this relationship for an automated packing algorithm selection is proposed. The effectiveness of the proposed framework is evaluated in the context of a large set of strip packing problem instances and the state-of-the-art strip packing algorithms. The results suggest a 91% accuracy in correctly identifying the best algorithm for a given instance.
本文研究了基于数据挖掘技术的条形包装元启发式算法选择。给定一组已解决的条形包装问题实例,学习实例特征与算法性能之间的关系,并用于预测解决一组新的未知问题实例的最佳算法。提出了一个能够对这种关系进行建模的框架,用于自动打包算法的选择。在大量条形布局问题实例和最先进的条形布局算法的背景下,评估了所提出框架的有效性。结果表明,在给定实例中正确识别最佳算法的准确率为91%。
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引用次数: 3
Solving the buffer allocation problem using simulation-based optimisation 使用基于模拟的优化解决缓冲区分配问题
Pub Date : 2021-02-01 DOI: 10.5784/36-2-684
J. Joubert, D. Kotzé
In production lines, buffers function as a means to decouple stations, which reduce the effect that station failures and varying process times have on the complete line’s throughput. However, adding larger buffers can be costly, for example, in the automotive industry where it results in increased working capital. This manuscript addresses the buffer allocation problem (BAP), seeking the smallest total buffer size while meeting a prescribed throughput by employing a simulation-based optimisation approach. A Tabu Search algorithm searches the solution space for the optimal buffer configuration while a discrete event simulation model evaluates each configuration, accounting for the machine (un)reliability. Since the multiple simulations add a sizeable computational burden, our approach introduces a novel neighbourhood search mechanism, which borrows from the Theory of Constrains. Solving test sets available in the literature suggest that this approach is 18 times faster than prior Adaptive Tabu Search approaches for small problems, and more than five times faster for medium-sized problems.
在生产线中,缓冲器的作用是将工位分离,从而减少工位故障和不同的工艺时间对整条生产线的吞吐量的影响。然而,增加更大的缓冲可能是昂贵的,例如,在汽车行业,它会导致增加的营运资金。本文解决了缓冲区分配问题(BAP),寻求最小的总缓冲区大小,同时通过采用基于模拟的优化方法满足规定的吞吐量。禁忌搜索算法在解空间中搜索最优缓冲区配置,而离散事件仿真模型评估每种配置,考虑机器(非)可靠性。由于多次模拟增加了相当大的计算负担,我们的方法引入了一种新的邻域搜索机制,该机制借鉴了约束理论。解决文献中可用的测试集表明,这种方法在小问题上比以前的自适应禁忌搜索方法快18倍,在中等问题上快5倍以上。
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引用次数: 1
On testing the hypothesis of population stability for credit risk scorecards 信用风险记分卡的人口稳定性假设检验
Pub Date : 2020-08-31 DOI: 10.5784/36-1-678
J. D. Pisanie, I. Visagie
Scorecards are models used in credit risk modelling. These models segments a population into various so-called risk buckets" based on the risk  characteristics of the individual clients. Once a scorecard has been developed, the credit provider typically prefers to keep this model in use for an extended period. As a result, it is important to test whether or not the model still ts the population. To this end, the hypothesis of population stability is tested; this hypothesis speci es that the current proportions of the population in the various risk buckets are the same as was the case at the point in time at which the scorecard was developed. In practice, this assumption is usually tested using a measure known as the population stability index (which corresponds to the asymmetric Kullback-Leibler discrepancy between discrete distributions) together with a well-known rule of thumb. This paper considers the statistical motivation for the use of the population stability index. Numerical examples are provided in order to demonstrate the e ect of the rule of thumb as well as other critical values. Although previous numerical studies relating to this statistic are available, the sample sizes are not realistic for the South African credit market. The paper demonstrates that the population stability index has little statisticalmerit as either a goodness-of- t statistic to test the hypothesis of population stability or as an intuitive discrepancy measure. As a result, a novel methodology for testing the mentioned hypothesis is proposed. This methodology includes a restatement of the hypothesis to specify a range of acceptable" deviations from the speci ed model. An alternative test statistic is also employed as discrepancy measure; this measure has the advantage of having a simple heuristic interpretation in the context of credit risk modelling. Key words: Goodness-of- t testing, hypothesis testing, population stability, risk analysis.
记分卡是信用风险建模中使用的模型。这些模型根据个人客户的风险特征将人群划分为各种所谓的“风险桶”。一旦记分卡被开发出来,信贷提供者通常倾向于在较长一段时间内保持该模型的使用。因此,检验模型是否仍然是总体是很重要的。为此,对种群稳定性假设进行了检验;这一假设说明,目前人口在各种风险桶中的比例与计分卡开发时的情况相同。在实践中,这个假设通常是用一种被称为人口稳定指数(它对应于离散分布之间的不对称Kullback-Leibler差异)的测量方法和一个众所周知的经验法则来检验的。本文考虑了使用人口稳定指数的统计动机。为了证明经验法则和其他临界值的作用,给出了数值例子。虽然以前有关于这一统计数字的研究,但样本量对于南非信贷市场来说是不现实的。本文论证了人口稳定指数作为检验人口稳定假设的t优性统计量或作为直观的差异度量,在统计上几乎没有什么价值。因此,提出了一种新的方法来检验上述假设。这种方法包括对假设的重述,以指定与指定模型的“可接受”偏差的范围。另一种检验统计量也被用作差异度量;该措施的优点是在信用风险建模的背景下具有简单的启发式解释。关键词:t检验,假设检验,群体稳定性,风险分析。
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引用次数: 3
Sentiment analysis of unstructured customer feedback for a retail bank 某零售银行非结构化客户反馈的情感分析
Pub Date : 2020-08-31 DOI: 10.5784/36-1-668
J. Kazmaier, JH van Vuuren
With the explosive growth of the Internet and social media, the communication model between an organisation and its customers has become  increasingly complex. A problem arises due to the sheer volume of unstructured data that has to be processed for the purposes of studying and addressing customer feedback. This calls for the development of automated methods. Important objectives of such methods include the detection of the underlying sentiment of customer feedback, as well as the synthesis and presentation of this sentiment in meaningful clusters such as topics and geographical locations. In this paper, a case study is conducted in which unstructured customer reviews related to products and services of a South African retail bank are evaluated by means of sentiment analysis. After suitable preprocessing techniques are applied to the reviews, the process of developing suitable models (primarily within the realm of machine learning) for detecting sentiment with a high level of performanceis described. Subsequently, model results are analysed, synthesised and visualised in order to extract valuable insight from the data. The ndings of the study show that custom learning-based models signi cantly outperform both pre-trained and commercial tools in sentiment classi cation. Furthermore, the analysis approach is shown to yield actionable information that may inform decision making. Key words: Data mining, decision support systems, neural networks, sentiment analysis.
随着互联网和社交媒体的爆炸式增长,组织与客户之间的沟通模式变得越来越复杂。一个问题是,为了研究和处理客户反馈,必须处理大量的非结构化数据。这就要求开发自动化的方法。这些方法的重要目标包括检测客户反馈的潜在情绪,以及在主题和地理位置等有意义的集群中综合和呈现这种情绪。在本文中,进行了一个案例研究,其中非结构化的客户评论相关的产品和服务的南非零售银行通过情绪分析的手段进行评估。在适当的预处理技术应用于评论之后,描述了开发合适的模型(主要在机器学习领域内)用于检测具有高水平性能的情绪的过程。随后,对模型结果进行分析、综合和可视化,以便从数据中提取有价值的见解。研究结果表明,基于定制学习的模型在情感分类方面明显优于预训练和商业工具。此外,分析方法显示可以产生可操作的信息,为决策提供信息。关键词:数据挖掘,决策支持系统,神经网络,情感分析。
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引用次数: 7
GARCH option pricing models in a South African equity context 南非股票背景下GARCH期权定价模型
Pub Date : 2020-08-31 DOI: 10.5784/36-1-676
PJ Venter, E. Maré
In this paper, di erent univariate GARCH option pricing models are applied to the FTSE/JSE Top 40 index to determine the best performing model  when modelling the implied South African Volatility Index (SAVI). Three di erent GARCH models (one symmetric and two asymmetric) are considered and three di erent log-likelihood functions are used in the model parameter estimation. Furthermore, the accuracy of each model is tested by comparing the GARCH implied SAVI to the historical SAVI. In addition, the pricing performance of each model is tested by comparing the GARCH implied price to market option prices. The empirical results indicate that the models incorporating asymmetric e ects outperform competing models in terms of pricing performance. Key words: Econometrics, nancial markets, pricing, stochastic processes.
本文将不同的单变量GARCH期权定价模型应用于FTSE/JSE top40指数,以确定在建模隐含南非波动率指数(SAVI)时表现最佳的模型。考虑了3个di 事件GARCH模型(1个对称和2个不对称),并使用3个di 事件对数似然函数进行模型参数估计。此外,通过比较GARCH隐含的SAVI和历史SAVI来检验每个模型的准确性。此外,通过比较GARCH隐含价格与市场期权价格,对各模型的定价性能进行了检验。实证结果表明,纳入不对称e 效应的模型在定价性能上优于竞争模型。关键词:计量经济学,金融市场,定价,随机过程。
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引用次数: 0
Editorial to Volume 36(1) 第36卷(1)社论
Pub Date : 2020-08-31 DOI: 10.5784/36-1-687
S. Terblanche
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引用次数: 0
Considering fairness in the load shedding scheduling problem 考虑公平性的减载调度问题
Pub Date : 2019-12-20 DOI: 10.5784/35-2-648
RG Rakotonirainy, I. Durbach, J. Nyirenda
Every day national power system networks provide thousands of MW of electric power from generating units to consumers, requiring different operations and planning to ensure secure systems. Where demand exceeds supply, load shedding - controlled, enforced reduction in supply - is necessary to prevent system collapse. Should load shedding need to be implemented, a planned schedule is necessary to allocate geographic areas on the required period of shedding. The problem of how to construct a schedule that fairly allocates load shedding responsibilities over geographic areas with minimum economic impacts is addressed in this paper. Two programming models are proposed. The first model consists of a linear integer programming model in which the objective is to minimise the economic cost subject to different fairness allocation constraints, while the second model involves formulation of the problem as a goal programming model in which different conflicting goals are simultaneously optimised. Several case studies are conducted in the context of a realistic, but hypothetical, scenario to explore the possible solutions that the proposed models provide. Results show that a fair schedule requires a high cost whereas lower cost can only be achieved with some sacrifices to the fairness of the schedule.
每天,国家电力系统网络从发电机组向消费者提供数千兆瓦的电力,需要不同的操作和规划来确保系统的安全。在需求超过供应的情况下,为了防止系统崩溃,必须削减负荷——有控制地、强制地减少供应。如果需要实施减载,则需要在所需减载期间分配地理区域的计划时间表。本文讨论了如何在地理区域内公平分配减载责任,并使经济影响最小化的问题。提出了两种规划模型。第一个模型包括一个线性整数规划模型,其目标是在不同的公平分配约束下最小化经济成本,而第二个模型涉及将问题表述为一个目标规划模型,其中不同冲突的目标同时优化。在一个现实但假设的场景中进行了几个案例研究,以探索所建议的模型提供的可能的解决方案。结果表明,公平的调度需要较高的成本,而较低的成本只能在一定程度上牺牲调度的公平性。
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引用次数: 0
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