Author: Elaheh Fata
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Languages : en
Pages : 62
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Book Description
We consider an assortment optimization problem where a customer chooses a single item from a sequence of sets shown to her, while limited inventories constrain the items offered to customers over time. In the special case where all of the assortments have size one, our problem captures the online stochastic matching with timeouts problem. For this problem, we derive a polynomial-time approximation algorithm which earns at least 1-ln(2-1/e), or 0.51, of the optimum. This improves upon the previous-best approximation ratio of 0.46, and furthermore, we show that it is tight. For the general assortment problem, we establish the first constant-factor approximation ratio of 0.09 for the case that different types of customers value items differently, and an approximation ratio of 0.15 for the case that different customers value each item the same. Our algorithms are based on rounding an LP relaxation for multi-stage assortment optimization, and improve upon previous randomized rounding schemes to derive the tight ratio of 1-ln(2-1/e).
Author: Yunzong Xu
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Languages : en
Pages : 59
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Motivated by several practical selling scenarios that require previous purchases to unlock future options, we consider a multi-stage assortment optimization problem, where the seller makes sequential assortment decisions with commitment, and the customer makes sequential choices to maximize her expected utility. We study the optimal solution to the problem when there are two stages. We show that this problem is polynomial-time solvable when the customer is fully myopic or fully forward-looking. In particular, when the customer is fully forward-looking, the optimal policy entails that the assortment in each stage is revenue-ordered and a product with higher revenue always leads to a wider range of future options. Moreover, we find that the optimal assortment in the first stage must be smaller than the optimal assortment when there were no second stage and the optimal assortment in the second stage must be larger than the optimal assortment when there were no first stage. When the customer is partially forward-looking, we show that the problem is NP-hard in general. In this case, we present efficient algorithms to solve this problem under various scenarios.We further extend the above results to the multi-stage problem with an arbitrary number of stages, for which we derive generalized structural properties and efficient algorithms. We also study the performance of a class of static policies and discuss the estimation problem of the multi-stage choice model.
Author: Basak Bebitoglu
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Languages : en
Pages : 30
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We study the assortment optimization problem in an online setting where a retailer uses multiple distribution centers to fulfill customer orders. Due to space, handling or other constraints, each distribution center can carry up to a pre-specified number of products. It is assumed that each distribution center is primarily responsible for a geographical region whose customers' choice is governed by a separate multinomial logit model. A distribution center can satisfy the demand from other regions, but this incurs an additional shipping cost for the retailer. The problem for the retailer is to determine which products to carry in each of its distribution centers and which products to offer for sale in each region so as to maximize its expected profit (revenue minus the shipping costs). We first show that the problem is NP-complete. We develop a conic quadratic mixed integer programming formulation and suggest a family of valid inequalities to strengthen this formulation. Numerical experiments show that our conic approach, combined with valid inequalities over-perform the mixed integer linear programming formulation and enables us to solve moderately sized instances optimally. We also study the effect of various factors such as the strength of the outside option, capacity constraint and shipping cost on company's profitability and assortment selection. Finally, we study the effect of not allowing cross-shipments or not considering them in assortment decisions and show that these may lead to substantial losses for an online retailer.
Author: Zhen Chen
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Languages : en
Pages : 0
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Assortment optimization is a fundamental problem in revenue management, in which the objective usually is to select a subset of products to offer to customers in order to maximize expected revenue or profit. However, business practices often involve multiple, and potentially conflicting goals. In this work, we propose a general framework and a novel reformulation method for solving multi-objective assortment optimization problems. Specifically, we consider problems with a separable sum of multiple convex objective functions on linear combinations of choice probabilities, and we present a reformulation that effectively "linearizes" the problem. We prove that the reformulated problem is equivalent to the original problem and that it leads to a unified solution approach to multi-objective assortment optimization problems in various contexts. We show that the approach encompasses a wide range of operational objectives, such as risk, customer utility, market share, costs with economies of scale, and dualized convex constraints. We first illustrate our approach with the multinomial logit model without any constraints or with allowance for totally unimodular constraints. We further show that our framework leads to tractable solutions under the nested logit model and the Markov chain choice model. Together with large-scale numerical experiments to demonstrate the efficiency and practicality of our methods, we highlight that our work provides a powerful and flexible tool for solving multi-objective assortment problems, which arise frequently in practical revenue management settings.
Author: Mohammed Ali Aouad
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Category :
Languages : en
Pages : 256
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Finding optimal product offerings is a fundamental operational issue in modern retailing, exemplified by the development of recommendation systems and decision support tools. The challenge is that designing an accurate predictive choice model generally comes at the detriment of efficient algorithms, which can prescribe near-optimal decisions. This thesis attempts to resolve this disconnect in the context of assortment and inventory optimization, through theoretical and empirical investigation. First, we tightly characterize the complexity of general nonparametric assortment optimization problems. We reveal connections to maximum independent set and combinatorial pricing problems, allowing to derive strong inapproximability bounds. We devise simple algorithms that achieve essentially best-possible factors with respect to the price ratio, size of customers' consideration sets, etc. Second, we develop a novel tractable approach to choice modeling, in the vein of nonparametric models, by leveraging documented assumptions on the customers' consider-then-choose behavior. We show that the assortment optimization problem can be cast as a dynamic program, that exploits the properties of a bi-partite graph representation to perform a state space collapse. Surprisingly, this exact algorithm is provably and practically efficient under common consider-then-choose assumptions. On the estimation front, we show that a critical step of standard nonparametric estimation methods (rank aggregation) can be solved in polynomial time in settings of interest, contrary to general nonparametric models. Predictive experiments on a large purchase panel dataset show significant improvements against common benchmarks. Third, we turn our attention to joint assortment optimization and inventory management problems under dynamic customer choice substitution. Prior to our work, little was known about these optimization models, which are intractable using modern discrete optimization solvers. Using probabilistic analysis, we unravel hidden structural properties, such as weak notions of submodularity. Building on these findings, we develop efficient and yet conceptually-simple approximation algorithms for common parametric and nonparametric choice models. Among notable results, we provide best-possible approximations under general nonparametric choice models (up to lower-order terms), and develop the first constant-factor approximation under the popular Multinomial Logit model. In synthetic experiments vis-a-vis existing heuristics, our approach is an order of magnitude faster in several cases and increases revenue by 6% to 16%.
Author: Heng Zhang
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Category :
Languages : en
Pages : 0
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We consider an assortment optimization problem where the customer may purchase multiple products and possibly more than one unit of each product purchased. We adopt the customer consumption model based on the Multiple-Discrete-Choice (MDC) model proposed by Huh and Li (2021). We identify conditions under which the profit-ordered sets are optimal. Without these conditions, we show that assortment optimization is NP-hard. Furthermore, we prove that a generalization of the profit-ordered sets achieves an approximation guarantee of 1/2. We also present an algorithm that computes an epsilon-optimal solution to the assortment problem in running time polynomial in 1/epsilon and the problem input size, once we impose the mild technical assumption that model parameters are bounded.
Author: Xin Chen
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Languages : en
Pages : 0
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We study an assortment optimization problem under a multi-purchase choice model in which customers choose a bundle of up to one product from each of two product categories. Different bundles have different utilities and the bundle price is the summation of the prices of products in it. For the uncapacitated setting where any set of products can be offered, we prove that this problem is strongly NP-hard. We show that an adjusted-revenue-ordered assortment provides a 1/2-approximation. Furthermore, we develop an approximation framework based on a linear programming relaxation of the problem and obtain a 0.74-approximation algorithm. This approximation ratio almost matches the integrality gap of the linear program, which is proven to be at most 0.75. For the capacitated setting, we prove that there does not exist a constant-factor approximation algorithm assuming the Exponential Time Hypothesis. The same hardness result holds for settings with general bundle prices or more than two categories. Finally, we conduct numerical experiments on randomly generated problem instances. The average approximation ratios of our algorithms are over 99%.
Author: James Mario Davis
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ISBN:
Category :
Languages : en
Pages : 424
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This thesis handles a fundamental problem in retail: given an enormous variety of products which does the retailer display to its customers? This is the assortment planning problem. We solve this problem by developing algorithms that, given input parameters for products, can efficiently return the set of products that should be displayed. To develop these algorithms we use a mathematical model of how customers react to displayed items, a customer choice model. Below we consider two classic customer choice models, the Multinomial Logit model and Nested Logit model. Under each of these customer choice models we develop algorithms that solve the assortment planning problem. Additionally, we consider the constrained assortment planning problem where the retailer must display products to customers but must also satisfy operational constraints.
Author: Chen, Xi
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ISBN:
Category :
Languages : en
Pages : 41
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Book Description
In this paper, we consider a personalized assortment planning problem under inventory constraints, where the type of each arriving customer is defined by a primary item of interest. As long as that item is in stock, the customer adds it to her shopping cart, at which point the retailer can recommend to the customer an assortment of add-ons to go along with her primary item. This problem is motivated by the new "recommendation at checkout'' systems that have been deployed at many online retailers, and also serves as a framework which unifies many existing problems in online algorithms (personalized assortment planning, single-leg booking, online matching with stochastic rewards). In our problem, add-on recommendation opportunities are eluded when primary items go out of stock, which poses additional challenges for the development of an online policy. We overcome these challenges by introducing the notion of an inventory protection level in expectation, and derive an algorithm with a 1/4 competitive ratio guarantee under adversarial arrivals.
Author: Omar El Housni
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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.
