TL;DR: Use a graph neural network to solve large-scale constrained assortment problems. 

Assortment optimization involves selecting a subset of substitutable products (subject to certain constraints) to maximize the expected revenue. It is a classic problem in revenue management and finds applications across various industries. However, the problem is usually NP-hard due to its combinatorial and non-linear nature. In this work, we explore how graph concolutional networks (GCNs) can be leveraged to efficiently solve constrained assortment optimization under the mixed multinomial logit choice model. We first develop a graph representation of the assortment problem, then train a GCN to learn the patterns of optimal assortments, and lastly propose two inference policies based on the GCN's output. Due to the GCN's inherent ability to generalize across inputs of varying sizes, we can use a GCN trained on small-scale instances to facilitate large-scale instances. Extensive numerical experiments demonstrate that given a GCN trained on small-scale instances (e.g., with 20 products), the proposed policies can achieve superior performance (90%+ optimality) on large-scale instances (with up to 2,000 products) within seconds, which outperform existing heuristic policies in both performance and efficiency. Furthermore, we extend our framework to a model-free setting where the underlying choice model is unknown but transaction data is available. We also conduct numerical experiments to demonstrate the effectiveness and efficiency of our proposed policies in this setting.

TL;DR: With very few resolvings, we can achieve constant regret (even without the non-degeneracy assumption) for OLP and NRM problems.

Online linear programming (OLP) has gained significant attention from both researchers and practitioners due to its extensive applications, such as online auction, network revenue management, order fulfillment and advertising. Existing OLP algorithms fall into two categories: LP-based algorithms and LP-free algorithms. The former one typically guarantees better performance, even offering a constant regret, but requires solving a large number of LPs, which could be computationally expensive. In contrast, LP-free algorithm only requires first-order computations but induces a worse performance, lacking a constant regret bound. In this work, we bridge the gap between these two extremes by proposing a well-performing algorithm, that solves LPs at a few selected time points and conducts first-order computations at other time points. Specifically, for the case where the inputs are drawn from an unknown finite-support distribution, the proposed algorithm achieves a constant regret (even for the hard 'degenerate' case) while solving LPs only O(log log T) times over the time horizon T. Moreover, when we are allowed to solve LPs only M times, we design the corresponding schedule such that the proposed algorithm can guarantee a nearly O(T^{(1/2)^{M-1}}) regret. Our work highlights the value of resolving both at the beginning and the end of the selling horizon, and provides a novel framework to prove the performance guarantee of the proposed policy under different infrequent resolving schedules. Furthermore, when the arrival probabilities are known at the beginning, our algorithm can guarantee a constant regret by solving LPs O(log log T) times, and a nearly O(T^{(1/2)^{M}}) regret by solving LPs only M times.  Numerical experiments are conducted to demonstrate the efficiency of the proposed algorithms. 

TL;DR: Use mobile ads to impact customers' engagement, which is a partially observed Markovian state, to boost revenue. 

We investigate a seller's optimal advertising campaign strategy targeting customers who interact with the seller over time. We model customers' engagement by a continuous-time Markov chain with two states, active and inactive. While in the active state, customers make purchases according to a Poisson process, with each purchase yielding a certain reward; in contrast, customers in the inactive state make no purchases. The seller can use advertisements to activate customers and the activation probability may be affected by customers' fatigue to promotion. The objective of the seller is to maximize the long-term average expected profit by designing an optimal ad campaign strategy based on customers' purchase histories. For a single customer without budget constraints, we demonstrate the optimality of a triple-threshold policy based on the elapsed time since the last purchase or ad campaign. Moreover, we find that the seller tends to push ads earlier to customers with high purchase rates and low recapture rates (i.e., low transition rates from an inactive state to an active state). Surprisingly, we also find that the seller should push ads earlier to customers with intermediate churn rates (i.e., intermediate transition rates from an active state to an inactive state) compared to those with small or large churn rates. When confronted with a budget constraint on the overall ad cost, we suggest first solving a relaxed problem and then implementing a separate triple-threshold policy for each customer with a specified budget. We establish the asymptotic optimality of this policy and show that the asymptotic loss order is O(\sqrt{\log T /T}) for the general problem and O(1/\sqrt{T}) for a special case. In addition, we explore the case with strategic customer reactions. Overall, our work reveals important insights of the optimal ad campaign problem and provides a useful strategy in practice.

TL;DR: Compare two widely adopted two-sided market business models, dealership and marketplace, by multi-period dynamic models. 

Problem Definition: We consider two business models for a two-sided economy under uncertainty: dealership and marketplace with fulfillment services. Although both business models can bridge the gap between demand and supply, it is not clear which model is better for the firm or for the consumers. Methodology/Results: We show that while the two models differ substantially in pricing power, inventory risk, fee structure, and fulfillment time, both models share several important features, with the revenues earned by the firm from the two models converging when the markets are thick. We also show that for thick markets there is a one-to-one mapping between their corresponding optimal policies. Managerial implications: Our results provide guidelines for firms entering two-sided markets: when the market is thick, the two business models are similar; when the market is thin, they should carefully inspect a number of market conditions before making the choice.

TL;DR: Compare the emission tax regulation and the emission permit regulation when the market demand is uncertain. 

Government regulations on emission control can be broadly divided into two categories: price instruments and quantity instruments. In this paper, we develop a stylized model to compare the two instruments in the presence of market uncertainty. We find that when the emission intensity (i.e., emissions per unit of production) and the market uncertainty are both high or low, the expected social welfare under the price instruments will be higher; otherwise, the performance of the quantity instruments is comparatively better. The results are robust when incorporating firm competition and national/regional pollution damage.  Afterward, we demonstrate that the government's quick-response capability or a hybrid of the price and quantity instruments can improve the expected social welfare, especially for high-emitting industries when the market uncertainty is intermediate. Lastly, for heterogeneous firms, we find that allowing permit trading in the quantity instrument may not be beneficial when pollution from each firm is more likely to have regional effects.