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Author: Alys Jiaxin Liang
Publisher:
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Languages : en
Pages : 0
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We consider a deterministic (fluid) multi-period assortment and inventory planning problem under the Multinomial Logit (MNL) choice model with dynamic (stockout-based) substitution, customer returns with a general return time distribution, and a cumulative capacity (storage) constraint for all products. Specifically, there is a one-time inventory decision at the beginning of the selling horizon and a customer who makes a purchase in the current period is allowed to return the purchase at a future period. The returned item will be inspected and, if it passes the inspection, it will be restocked and becomes available again for sale in the next period. The objective of the firm is to identify the initial inventories of the products that maximize the total profit throughout the horizon. Due to the dynamics created by the dynamic substitution and customer returns, this is a technically challenging problem to solve. Unlike in the setting without returns where a product will no longer be available throughout the remaining periods after it stocks out, in the presence of returns, a product could again be available due to restocked returns and may even stock out again, and this cycle might continue for several times depending on the availability of other products. We focus on the fluid version of this problem and develop a linear program (LP)-based approach to exactly solve this problem. If the LP has a unique optimal solution, then this solution is also an optimal solution to our problem. If, however, the LP does not have a unique optimal solution, an arbitrary optimal solution of the LP may not be feasible for our problem. To deal with this scenario, we develop an algorithm using which, given any optimal LP solution, we can construct an alternative optimal LP solution that is also optimal for our problem. The algorithm uses both primal and dual LP solutions together with exploiting some key structural properties of the problem. We visualize our approach using illustrative examples.
Author: Alys Jiaxin Liang
Publisher:
ISBN:
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Languages : en
Pages : 0
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Book Description
We consider a deterministic (fluid) multi-period assortment and inventory planning problem under the Multinomial Logit (MNL) choice model with dynamic (stockout-based) substitution, customer returns with a general return time distribution, and a cumulative capacity (storage) constraint for all products. Specifically, there is a one-time inventory decision at the beginning of the selling horizon and a customer who makes a purchase in the current period is allowed to return the purchase at a future period. The returned item will be inspected and, if it passes the inspection, it will be restocked and becomes available again for sale in the next period. The objective of the firm is to identify the initial inventories of the products that maximize the total profit throughout the horizon. Due to the dynamics created by the dynamic substitution and customer returns, this is a technically challenging problem to solve. Unlike in the setting without returns where a product will no longer be available throughout the remaining periods after it stocks out, in the presence of returns, a product could again be available due to restocked returns and may even stock out again, and this cycle might continue for several times depending on the availability of other products. We focus on the fluid version of this problem and develop a linear program (LP)-based approach to exactly solve this problem. If the LP has a unique optimal solution, then this solution is also an optimal solution to our problem. If, however, the LP does not have a unique optimal solution, an arbitrary optimal solution of the LP may not be feasible for our problem. To deal with this scenario, we develop an algorithm using which, given any optimal LP solution, we can construct an alternative optimal LP solution that is also optimal for our problem. The algorithm uses both primal and dual LP solutions together with exploiting some key structural properties of the problem. We visualize our approach using illustrative examples.
Author: Dorothee Honhon
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
We present an efficient dynamic programming algorithm to determine the optimal assortment and inventory levels in a single-period problem with stockout-based substitution. In our model, total customer demand is random and comprises of a fixed proportion of customers of different types. Customer preferences are modeled through the definition of these types. Each customer type corresponds to a specific preference ordering amongst products. A customer purchases the highest ranked product according to his type (if any) that is available at the time of his visit to the store (stockout-based substitution). We solve the optimal assortment problem using a dynamic programming formulation. We establish structural properties of the value function of the dynamic program that, in particular, help characterize multiple local maxima. We use the properties of the optima to construct a method for efficiently solving the problem in pseudopolynomial time. Our algorithm also gives a heuristic for the general case, i.e., when the proportion of customers of each type is random. In numerical tests, this heuristic performs better and faster than previously known methods, especially when the average demand and the degree of substitutability amongst products are high.
Author: Omar El Housni
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
We study a joint assortment and inventory optimization problem faced by an online retailer who needs to decide on both the assortment along with the inventories of a set of N substitutable products before the start of the selling season to maximize the expected profit. The problem raises both algorithmic and modeling challenges. One of the main challenges is to tractably model dynamic stock-out based substitution where a customer may substitute to the most preferred product that is available if their first choice is not offered or stocked-out. We first consider the joint assortment and inventory optimization problem for a Markov Chain choice model and present a near-optimal algorithm for the problem. Our results significantly improve over the results in Gallego and Kim (2020) where the regret can be linear in T (where T is the number of customers) in the worst case.We build upon their approach and give an algorithm with regret Õ( sqrt{NT}) with respect to an LP upper bound. Our algorithm achieves a good balance between expected revenue and inventory costs by identifying a subset of products that can pool demand from the universe of substitutable products without significantly cannibalizing the revenue in the presence of dynamic substitution behavior of customers. We also present a multi-step choice model that captures the complex choice process in an online retail setting characterized by a large universe of products and a heavy-tailed distribution of mean demands. Our model captures different steps of the choice process including search, formation of a consideration set and eventual purchase. We conduct computational experiments that show that our algorithm empirically outperforms previous approaches both on synthetic and realistic instances.
Author: Jingwei Zhang
Publisher:
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Languages : en
Pages : 0
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Book Description
We study the joint assortment and inventory planning problem with stockout-based substitution. In this problem, we pick the number of units to stock for the products at the beginning of the selling horizon. Each arriving customer makes a choice among the set of products with remaining on-hand inventories. Our goal is to pick the stocking quantities to maximize the total expected revenue from the sales net of the stocking cost. Using a fluid approximation for the problem, we give solutions with performance guarantees that significantly improve earlier results. Letting $T$ be the number of time periods in the selling horizon and $n$ be the number of products, when customers choose under a general choice model, we show that we can round the solution to the fluid approximation to obtain stocking quantities with an optimality gap of $O(n + sqrt{nT})$, improving earlier optimality gaps by a logarithmic factor. More importantly, when customers choose under the multinomial logit model, we develop a rounding scheme that uses the solution to the fluid approximation to generate stocking quantities with an optimality gap of $O( log T sqrt{T log T})$. The optimality gap that we give under the multinomial logit model is the first one that does not depend on the number of products. Such an optimality gap has important implications in the many-products regime. Earlier results cannot guarantee that the stocking quantities generated by the fluid approximation perform well when both the demand volume and number of products are large, which is a regime becoming more relevant for online retail applications with large product variety. In contrast, we can guarantee that the stocking quantities generated by our rounding scheme perform well when both the demand volume and number of products are large.
Author: Ali Aouad
Publisher:
ISBN:
Category :
Languages : en
Pages : 53
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Book Description
We study the dynamic assortment planning problem under the widely-utilized Multinomial Logit choice model (MNL). In this single-period assortment optimization and inventory management problem, the retailer jointly decides on an assortment, i.e., a subset of products to be offered, as well as on the inventory levels of these products, aiming to maximize the expected revenue subject to a capacity constraint on the total number of units stocked. The demand process is formed by a stochastic stream of arriving customers, who dynamically substitute between products according to the MNL model. This modeling approach has motivated a growing line of research on joint assortment and inventory optimization, initiated by the seminal papers of Bassok et al. (1999) and Mahajan and van Ryzin (2001). The currently best-known provably-good approximation in the dynamic setting considered, recently devised by Aouad et al. (2018b), leads to an expected revenue of at least 0.139 times the optimum under increasing-failure rate demand distributions, far from being satisfactory in practical revenue management applications. In this paper, we establish novel stochastic inequalities showing that, for any given inventory levels, the expected demand of each offered product is "stable" under basic algorithmic operations, such as scaling the MNL preference weights and shifting inventory across certain products. By exploiting this newly-gained understanding, we devise the first approximation scheme for dynamic assortment planning under the MNL model, allowing one to efficiently compute inventory levels that approach the optimal expected revenue within any degree of accuracy. Our approximation scheme is employed in extensive computational experiments to concurrently measure the performance of various algorithmic practices proposed in earlier literature. These experiments provide further insights regarding the value of dynamic substitution models, in comparison to simple inventory models that overlook stock-out effects, and shed light on their real-life deployability.
Author: Joonkyum Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 43
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Book Description
We demonstrate the value of utility-based choice models to estimate demand and plan inventory for new and used textbooks in the presence of consumer choice and stockout-based substitution at a university textbook retailer. Demand information is censored, the exact time of stockout is not observed, and the short selling season often does not allow for replenishment. Using data for 26,749 book titles from 2007 to 2011 and a simulation experiment calibrated on real data, we show that an attribute-based choice model generates accurate demand estimates (mean absolute percentage error less than 1%) even when nearly 90% of the textbooks in the fit sample experience stockout. This performance is driven by the heterogeneity of product attributes and is robust to the occurrence of product returns. We implement this model at the bookstore in a controlled field experiment and obtain over 10% increase in profit. The results show that accounting for asymmetric and stockout-based substitution in demand estimation and inventory planning enables us to make systematic corrections in inventory mix and inventory level compared to the existing process.
Author: Vishal Gaur
Publisher:
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Category :
Languages : en
Pages :
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Book Description
We consider a single-period assortment planning and inventory management problem for aretailer, using a locational choice model to represent consumer demand. We first determinethe optimal variety, product location, and inventory decisions under static substitution, andshow that the optimal assortment consists of products equally spaced out such that there is nosubstitution among them regardless of the distribution of consumer preferences. The optimalsolution can be such that some customers prefer not to buy any product in the assortment, andsuch that the most popular product is not offered.We then obtain bounds on profit when customers dynamically substitute, using the staticsubstitution for the lower bound, and a retailer-controlled substitution for the upper bound.We thus define two heuristics to solve the problem under dynamic substitution, and numericallyevaluate their performance. This analysis shows the value of modeling dynamic substitution andidentifies conditions in which the static substitution solution serves as a good approximation.
Author: Vineet Goyal
Publisher:
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Languages : en
Pages : 0
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Assortment planning of substitutable products is a major operational issue that arises in many industries, such as retailing, airlines and consumer electronics. We consider a single-period joint assortment and inventory planning problem under dynamic substitution with stochastic demands, and provide complexity and algorithmic results as well as insightful structural characterizations of near-optimal solutions for important variants of the problem. First, we show that the assortment planning problem is NP-hard even for a very simple consumer choice model, where each customer is willing to buy only two products. In fact, we show that the problem is hard to approximate within a factor better than 1-1/e. Secondly, we show that for several interesting and practical choice models, one can devise a polynomial-time approximation scheme (PTAS), i.e., the problem can be solved efficiently to within any level of accuracy. To the best of our knowledge, this is the first efficient algorithm with provably near-optimal performance guarantees for assortment planning problems under dynamic substitution. Quite surprisingly, the algorithm we propose stocks only a constant number of different product types; this constant depends only on the desired accuracy level. This provides an important managerial insight that assortments with a relatively small number of product types can obtain almost all of the potential revenue. Furthermore, we show that our algorithm can be easily adapted for more general choice models, and present numerical experiments to show that it performs significantly better than other known approaches.
Author: Martin K. Starr
Publisher: Taylor & Francis
ISBN: 1317419243
Category : Business & Economics
Languages : en
Pages : 712
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Book Description
This remarkable volume highlights the importance of Production and Operations Management (POM) as a field of study and research contributing to substantial business and social growth. The editors emphasize how POM works with a range of systems—agriculture, disaster management, e-commerce, healthcare, hospitality, military systems, not-for-profit, retail, sports, sustainability, telecommunications, and transport—and how it contributes to the growth of each. Martin K. Starr and Sushil K. Gupta gather an international team of experts to provide researchers and students with a panoramic vision of the field. Divided into eight parts, the book presents the history of POM, and establishes the foundation upon which POM has been built while also revisiting and revitalizing topics that have long been essential. It examines the significance of processes and projects to the fundamental growth of the POM field. Critical emerging themes and new research are examined with open minds and this is followed by opportunities to interface with other business functions. Finally, the next era is discussed in ways that combine practical skill with philosophy in its analysis of POM, including traditional and nontraditional applications, before concluding with the editors’ thoughts on the future of the discipline. Students of POM will find this a comprehensive, definitive resource on the state of the discipline and its future directions.
Author: Anna-Lena Sachs
Publisher: Springer
ISBN: 3319133055
Category : Business & Economics
Languages : en
Pages : 126
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Book Description
This book addresses the challenging task of demand forecasting and inventory management in retailing. It analyzes how information from point-of-sale scanner systems can be used to improve inventory decisions, and develops a data-driven approach that integrates demand forecasting and inventory management for perishable products, while taking unobservable lost sales and substitution into account in out-of-stock situations. Using linear programming, a new inventory function that reflects the causal relationship between demand and external factors such as price and weather is proposed. The book subsequently demonstrates the benefits of this new approach in numerical studies that utilize real data collected at a large European retail chain. Furthermore, the book derives an optimal inventory policy for a multi-product setting in which the decision-maker faces an aggregated service level target, and analyzes whether the decision-maker is subject to behavioral biases based on real data for bakery products.
