BCORLE($\lambda$): An Offline Reinforcement Learning and Evaluation Framework for Coupons Allocation in E-commerce Market
Authors: Yang Zhang
Bo Tang
Qingyu Yang
Dou An
Hongyin Tang
Chenyang Xi
Xueying LI
Feiyu Xiong
Venue: NeurIPS 2021 Poster (2021)
Keywords: Application of E-commerce Market；Coupons Allocation
Constrained Markov Decision Process
Offline Reinforcement Learning
Off-policy Evaluation

Abstract: Coupons allocation is an important tool for enterprises to increase the activity and loyalty of users on the e-commerce market. One fundamental problem related is how to allocate coupons within a fixed budget while maximizing users' retention on the e-commerce platform. The online e-commerce environment is complicated and ever changing, so it requires the coupons allocation policy learning can quickly adapt to the changes of the company's business strategy. Unfortunately, existing studies with a huge computation overhead can hardly satisfy the requirements of real-time and fast-response in the real world. Specifically, the problem of coupons allocation within a fixed budget is usually formulated as a Lagrangian problem. Existing solutions need to re-learn the policy once the value of Lagrangian multiplier variable $\lambda$ is updated, causing a great computation overhead. Besides, a mature e-commerce market often faces tens of millions of users and dozens of types of coupons which construct the huge policy space, further increasing the difficulty of solving the problem. To tackle with above problems, we propose a budget constrained offline reinforcement learning and evaluation with $\lambda$-generalization (BCORLE($\lambda$)) framework. The proposed method can help enterprises develop a coupons allocation policy which greatly improves users' retention rate on the platform while ensuring the cost does not exceed the budget. Specifically, $\lambda$-generalization method is proposed to lead the policy learning process can be executed according to different $\lambda$ values adaptively, avoiding re-learning new polices from scratch. Thus the computation overhead is greatly reduced. Further, a novel offline reinforcement learning method and an off-policy evaluation algorithm are proposed for policy learning and policy evaluation, respectively. Finally, experiments on the simulation platform and real-world e-commerce market validate the effectiveness of our approach.

BCORLE(X): An Offline Reinforcement Learning and Evaluation Framework for Coupons Allocation in E-commerce Market
Yang Zhang*
Bo Tang Alibaba Group
Faculty of Electronics and Information Xi'an an Jiaotong University
Qingyu Yang
Dou An
Faculty of Electronics and Information Xi' an Jiaotong University
Faculty Electronics and Information Xi'an an Jiaotong University
Hongyin Tang
Chenyang Xi Alibaba Group
Xueying Li Alibaba Group
Feiyu Xiong Alibaba Group
Institute Software Chinese Academy of Sciences
Abstract
Coupons allocation an important tool for enterprises to increase the activity and loyalty of users on the e-commerce market. One fundamental problem related is how allocate coupons within a fixed budget while maximizing users' retention on the e-commerce platform. The online e-commerce environment is compli- cated and ever changing, so requires the coupons allocation policy learning can quickly adapt to the changes of the company's business strategy. Unfortu- nately, existing studies with a huge computation overhead can hardly satisfy the requirements of real-time and fast-response in the real world. Specifically, the problem of coupons allocation within fixed budget is usually formulated as a Lagrangian problem. Existing solutions need to re-learn the policy once the value Lagrangian multiplier variable À updated, causing a great computation over- head. Besides, mature e-commerce market often faces tens of millions of users and dozens of types of coupons which construct the huge policy space, further increasing the difficulty of solving the problem. To tackle with above problems, propose a budget constrained offline reinforcement learning and evaluation with >-generalization (BCORLE() (()) framework. The proposed method help enter- prises develop a coupons allocation policy which greatly improves users' retention rate the platform while ensuring the cost does not exceed the budget. Specifi- cally, >-generalization method is proposed to lead the policy learning process can be executed according different values adaptively, avoiding re-learning new polices from scratch. Thus the computation overhead is greatly reduced. Further, a novel offline reinforcement learning method and an off-policy evaluation algorithm are proposed for policy learning and policy evaluation, respectively, Finally, exper- iments on the simulation platform and real-world e-commerce market validate the effectiveness of our approach.
"ork was done during an internship at Alibaba Group. 1 "Coresoondnneyyanginngeeeee mail.xjtu.edu.cn
35th Conference on Neural Information Processing Systems (NcurIPS 2021).

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Introduction
With the development of the internet industry, the business competition between e-commerce plat- forms is becoming more and more fierce. It is common for the e-commerce platform to provide users with incentives in the form of monetary prize to attract users to take actions of clicks or conversions For instance, on online e-commerce market, such as Taobao and Amazon, every day an e-commerce platform sends a coupon to each user who logs on the platform to keep them high retention the platform. Obviously, the larger value of distributed coupons is, the higher retention rate of users it will gain. However, it may bring huge financial loss to the platform when coupons allocation is too costly. Thus, it is key problem for the platform to decide an appropriate value of each coupon maximizing the users' retention while limiting the cost not to exceed a fixed budget. Besides, tens of millions of users and dozens of types of coupons lead to an extremely large policy space, which greatly increases the difficulty for solving the problem.
3 35 4T.
The budget constrained coupons allocation problem is usually formulated as a constrained Markov decision process (CMDP), and then can be converted into a Lagrangian dual problem. In related studies [20 28 35,, bisection search or gradient descent is used to find the optimal value of Lagrangian multiplier variable X, and the corresponding optimal coupons allocation policy for given À is learned using reinforcement learning (RL) methods. Here, offline RL methods are used to avoid potential financial risks in learning process as the budget cannot be recovered once dispensed. Unfortunately, a key problem is that the policy needs be re-learned every time when the value of À is updated until the budget constraint is satisfied. Such a repetitive policy learning process brings a great computation overhead, making existing studies unable to satisfy the real-time and fast response requirements in the complicated industrial world. Thus the applications of existing methods are limited.
To address this problem, we propose X-generalization method which is also technique of multi- objective RL M.. The key idea behind our method is that the tasks of finding optimal value of À and learning optimal policy are combined by extending the reward function and training dataset with different values of X. Thus, the optimal policy can be learned with different values of À adaptively and the policy learning process only needs to be performed once. Besides, there is another advantage of our method is that there is no need to re-learn the policy when the budget changes. We only need to select an appropriate value of À which makes its corresponding optimal policy satisfy the new budget constraint. It can help our method respond quickly to the changing business strategy of the company.
The contribution of this work is four-fold. First, budget constrained offline reinforcement learning and evaluation with X-generalization (BCORLE(A)) framework is proposed to solve the CMDP problem of coupons allocation. BCORLE(A) framework consists of X-generalization method, an offline policy learning method and an off policy evaluation method, in which X-generalization method is proposed to reduce the computation overhead of policy learning. Second, for policy learning, an improved offline RL algorithm called resemble batch-cone constrained Q-learning (R-BCQ) is proposed in this paper. R-BCQ combines the advantages of two popular offline RL methods: batch-constrained Q-learning (BCQ) 13 and random ensemble mixture (REM) [. Specifically, R-BCQ addresses the problem of extrapolation error like BCQ, and retains strong generalization ability like REM. Third, to evaluate the performance of learned policy, a model-free off-policy evaluation method called random ensemble mixture evaluator (REME) is proposed. Finally, the experiments on simulation platform and a real mobile shopping app validate the effectiveness of the proposed methods.
2 Related Work
Exiting works about the CMDP can be divided into three classes according to the constraint type:
33 refers that there unsafe states in the full set of states. The objective of the agent is to maximize the cumulative rewards while avoiding falling into unsafe states. In recent studies, Wachi and Sui 32 explored the safe region using step-wise approach, while Turchetta et al. [30 proposed a hierarchical RL method that a teacher instructs the student to take safe policy. Besides, Lyapumov function [5] was also used in exploring safe RL.
State constrained MDP, also called safe RL [14]
Action constrained MDP refers that the action taken by the agent limited by a constraint. Appar- ently, the problem studied in this paper belongs to this CMDP type because selecting the value of distributed coupons is the action of agent and it constrained by the budget. This kind of problem commonly formulated as Lagrangian problem. The aim of solving this problem is to find an optimal

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Lagrangian multiplier variable À and the corresponding optimal policy satisfying the constraint, For find an optimal value of X, and a stochastic gradient descent method is proposed to learn the policy in 35 Another approach is to use the gradient descent method to find the optimal value of X, and the corresponding policy is developed by fitted- -eler-nnn method [20] or actor-critic method [28]. A key problem in existing approaches is that they both need to update the value of À many times, and the policy needs to be re-learned once the value of is updated, which poses great computation overhead of policy learning and limits their application in real world. In this paper, we propose a X-generalization based method to solve this problem.
instance, a bisection search is developed
State-action constrained MDP is generalization of first two CMDP types. In this CMDP type, constraint is imposed both on the state and action. Existing studies about this type focus on finding a solution to the non-convex optimization problem in a Lagrangian dual form in theory [7] [3 37]
which is not strongly relevant the work in this paper, so they will not be introduced detail.
More related work about offline RL. and off-policy evaluation are presented in Appendix A
Problem Formulation
In this section, the problem of coupons allocation with budget is first formulated as constrained Markov Decision Process, and then converted into a Lagrangian dual problem.
3.1 CMDP Problem of Coupons Distribution
In this paper, the time horizon of coupons allocation problem is divided into T days. Every day, each user receives a coupon after logging into the e-commerce platform. The problem of coupons allocation with a predefined budget is formulated as a CMDP, which is defined as < S, A, P. R, C, Y, b >. S denotes the state space that consists of user features and historical retention information of the user on shopping platform. A denotes the action space containing the candidate values of a coupon. P denotes the probability of the state transition after taking some action S x A S - [0, 1]. R denotes the reward function defined as the user's s retention information the next day after receiving a coupon;
namely, the reward is ( if the user logs in the platform tomorrow; otherwise, it is - -1 C denotes
the cost function defined as the value of the distributed coupon. E [0, 1] and y E [0. 1] denote the discount factors used weight future reward and weight future cost, respectively. denotes the budget constraint of the coupons allocation in 7 days.
The aim of the platform is to develop an optimal policy maximizing the cumulative reward while preventing the cost from exceeding the budget. To avoid potential financial risks in the online interaction between agent and environment when using online RL methods, the CMDP problem is solved using an offline RL method in this paper. Namely, the optimal policy is developed from a fixed data 1 that is collected from the past interactions between the agent and the environment using a past behaviour policy Th- The fixed dataset D consists of M tuples: D = {(8;, ag T', Ci 81+1)) M M Accordingly, the CMDP problem can be formulated as:
max (Tx) = E,
-E=07 subject to C(T) = E, E Yd c
< (1)
where ा denotes the learned policy, II is the collection of all policies, and T is the trajectorics distribution that follows the policy and an initial state distribution J..
3.2 Lagrangian Dual Problem
To solve the CMDP problem defined by Eq. first, the CMDP problem is converted into its Lagrangian problem as follows:
max L(TT subject to A 0
(2)
where T(TT,A) = J(m) - ((C(m)) - b), and represents the Lagrangian multiplier variable.
Assumption 1. There exists policy that satisfies the constraint C(T) < b.
This assumption is true in the real world; otherwise, the amount of distributed coupon can be reduced to satisfy the constraint. Since the Assumption [ the Slater's 's condition 77] holds. Therefore the problem of 2 is equivalent its Lagrangian dual problem, which can be expressed as: min max L(T,
(3)
XER NEll
3

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Offine Polcc
Teaming Matael
Learned Policy
Train
Opiznal polacy with
Office Polky
Esolaticn (REME)
(R-BCQ)
Lincer Combiauiio
Cheeac saidia
Head
Reez
Bool
Haad
Hoall
Pelicy bvalstin
Loining
Pratusice retwodk
Collective
Soate
satiane
Pulay Leanzn
Generative
Allassite
Office
S-Cencliation
Palay
offiin
des
Figure BCORLE(A) framework consists of three methods: R-BCQ, REME and X-generalization method. After policy learning and evaluation, a Lagrangian variable and its corresponding optimal policy that makes the cost closest to but not larger than the budget is selected as the final policy.
To solve the Lagrangian dual problem, is needed to find an optimal value of Lagrangian variable X and the corresponding optimal policy T.. And the proof of the existence of the solution of the Lagrangian dual problem is given in the Appendix B
Our Approach
In this section, propose BCORLE(A) framework to solve the Lagrangian problem of budget constrained coupons allocation. BCORLE(A) framework consists of three methods: R-BCQ method for offlin policy learning, REME method for off-policy evaluation, and X-generalization method for making the policy learning and evaluation process can be performed with different values of À to reduce the computation overhead. Figure I provides summary depiction of BCORLE(A) framework.
4.1 >-Generalization
To solve the problem of coupons allocation, the Lagrangian problem defined by Eq. is transformed into a RL problem as follows.
T
L [ 2) (TT) x+ x+ (C b)) = Σ r (8c, ae)
Σ
(sc. ar)
-b)
(4)
E
r (st, at) (st, + Ab = E
(se, ac)
Ab.
Subsuming the cost into the reward function, we obtain the final reward function to be optimized x = r rst,, a.) Ac (s,, az). Therefore, the offline RL method can be used to develop optimal
offline policy maximizing E
Σ pd (st, at) under the constraint of budget.
Different from common RL problem, there Lagrangian multiplier variable in the reward function. Therefore, the optimal policy changes with the value of X. To learn the optimal policy while ensuring the cost not to exceed the budget, existing works 220 35 both employ a X-update based framework, which is shown in the left of Figure 2 Specifically, for given X, existing methods both first conduct the policy learning process to find corresponding optimal policy. Then the policy evaluation process is conducted judge whether the cost of the learned policy falls within a
Optimal policy with
Optimal policy with
satietes ox A.A)
Evalution
Policy Evaluation
Policy Learzing
Policy Learning
small range of the budget without excceding the budget (i.c.
E, [ A)) E [b 8, b] where 5 denotes the lower bound of cost). If not, the value of À will be updated by bisection method (35 or gradient descent method (20), and then the policy learning process will be executed again until the termination condition satisfied. However, it is necessary for existing methods to re-learn the policy once the value of À is updated, causing huge computation overhead.
Updat: Lamisis
Zegenclication
Exitted methed
Our method
Figure 2: comparison between the ex- isting method in 20 35 and our method.

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To address this problem, we propose X- gegnrallization method based on the idea of multi-objective RL method [TT]. The key idea of X-generalization method is to combine two tasks of finding the optimal value of À and policy learning together by extending the variable À into the transition tuple, thus the policy learning process can be conducted to learn the optimal policy with different values of À adaptively. Then, the policy evaluation process is conducted to select the value of X and the corresponding optimal policy which satisfies the termination condition as the final policy. Requiring not updating the value of X, the proposed method makes the policy learning and evaluation processes only need to be executed once. Thus, the computation overhead is greatly reduced in our method compared with existing methods. Besides, another advantage of our method is that when the budget changes, there is no need to re-learn the policy. We only need to reselect a value of À which makes its corresponding policy satisfy the constraint of budget. It helps our method respond quickly to the changing company's s business strategy. The flow chart of our method is shown in the right of Figure 2
Specifically, the proposed X-generalization method first increases the size of training dataset under different values of X. For each transition tuple (si,as; as To; Ct, 8141), we enlarge
into {(s,, a;, r , C2. 81+1: : where >; E {2,, Ar.3 and Ty Ay is defined in Eq. 4
Therefore, the original training dataset D = {(s;; a,, TA, C2 S4+ | is enlarged into D' M.J.
{(s;, 0z, r 7 G4 8141, Aj)) (14); we give a detailed introduction about how to determine the candidate value set of À in Appendix C
1.j=1.1 which is times as the size of D. It is important to note that
The new dataset D' integrates the state, action and the variable X. and ensures the processes of policy learning and evaluation are conducted with different values of X. For each value of X, the policy learning network generates a policy π (s, A), and then the policy evaluation network generates a value Ö (a (s, A)) to evaluate the learned policy. Finally, choose the value of À and the corresponding policy π (s, A) which satisfies IE, Ö (TT (s, A)) E [b- 10-6, 6,6] the final optimal policy.
4.2 Offline Policy Learning: R-BCQ
There are two types of popular offline RL methods: BCQ method and REM method. Two methods have their own advantages. BCQ addresses the problem of extrapolation error via ensuring the match between the state-action pairs generated using the learned policy and the fixed training dataset. REM has high robustness and strong generalization ability with the multi-head network. Unfortumately, the performances of two methods are significantly different on different datasets and it is difficult to judge which of two methods would perform better in the coupons allocation problem of e-commerce market. Thus in this paper, new method that combines the advantages of two methods is proposed.
Due to the limited size of the fixed training dataset, some state-action pairs generated in learning may not exist in the training dataset. This mismatch causes the estimated value of some state-action pairs deviate greatly from the true value, thus damages the performance of learned policy. To address this problem, we introduce generative model that imitates the policy in existing dataset. Specifically, the generative model is denoted as G(a]s, x; w) that represents an estimation of the behavior policy Te for given state and Lagrangian variable À with parameters w. When selecting action, we only choose the action which satisfies G (a s, w;w) / max G (āls, X; w) > 3 from the action space, where 33 is a threshold to drop state-action pairs which do not exist or seldom appear in the training dataset.
After choosing candidate action set using the generative model, the policy learning process is conducted using a multi-head network. Each head in the network represents an estimation of the Q-value of the state-action pair. Next, convex combination of all heads of the network is used as the final estimated Q- Q-value. Compared to common one-head network, multi-head network avoids the Q-value estimation bias problem, thus increases the robustness and generalization ability of the policy learning network. Combined with X-generalization method, the policy learning network has three inputs: state 8, action a and Lagrangian multiplier variable X. Each head of the network is denoted as (s,s, a, A) and the final estimated Q- Q-value is defined as Q(s, a, A) = Σ. a,Q; (s, a, X) where a; is the weight of each head and Σ, ag 1, a; > 0, Vi.
Combined with the generative model G(als, X; w), the learned policy is denoted as follows.
π (s. A) a/G( G( 25
arg max
E, E,ali (s,a,
(5)
5

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And the loss of training the policy learning network with parameters @ is defined as follows.
(0)
of D'
Iu
a'IG(("(=")/ max G(al=")> E, ai (d',',>) E, aiQi
The generative model is updated with the loss L (w) = Es,anDrr [-log G (als, };w]].
4.3 Policy Evaluation: REME
great challenge for the application of offiine RL method in real world is develop an off-policy evaluation mechanism to evaluate the cost and expected utility of policy accurately. To tackle this challenge, in this section, model-free direct evaluation method called REME is proposed.
The proposed REME method employs multi-head evaluation network to evaluate the policy and uses an iterative update mechanism to train the evaluation network. Specifically, each head of the evaluation network represents an evaluated value of the given policy, and a convex combination of all heads is used as the final evaluated value. Unlike using the max operator when calculating the target value in the policy learning, compute the target value using the evaluated policy in policy evaluation. Besides, combined with the X- g-genraalization method, the policy evaluation network is able to evaluate the policy и with different values of A. The evaluated network with parameters 0 is updated according to the loss:
L( of [Ie (r++ as (5' (s - E, an as,
Note that when estimating the cost Č(T) of a given policy x, we will use the cost c to replace the reward in Eq. 7
We summarize the steps of the R-BCQ, REME and BCORLE()) algorithms in Appendix D
Experiments
In experiments, study four questions: (1) Does >-generalization method help to reduce the computation overhead of policy training? (2) How does BCORLE(A) framework with R-BCQ algorithm perform in comparison other state-of-the-art offline RI algorithms?
(3) How does REME algorithm perform in comparison to other OPE algorithms? (4) How do different values of in X-generalization method affect the performance of proposed approach? To answer these questions. we conduct experiments both on simulation platform and real-world e-commerce platform.
5.1 Simulation Experiments
Before conducting experiments on the real-world platform, we perform the experiments on the simulation platform to ensure there is no risk or unaffordable cost when using the proposed method.
5.1.1 Simulation Environment Setup
According to the background knowledge real-world e-commerce platform, we create a simulation environment that can be seen as a simplification of real-world e-commerce platform. There are 10000 users in the simulation environment. Each user may log into the simulation platform according to the user preference, and the user will receive coupon after logging. We simulate the user preference using random distributions. For example, assuming there is a user named "Alice" in the simulation environment. There are two logs into the simulation platform, she will receive a coupon G. And on the next day, "Alice" would logs into the platform with the probability Pe.. that is sampled randomly from a uniform distribution with a precondition: Pc, 2 Po, if c 2 Cy. 2) One day when "Alice" doesn't 't log in the simulation platform, the probability P' of whether she will log into the platform next day is sampled from another uniform distribution and satisfies P' < Pa., Vc,.
of how she would act in the environment: 1) One day when " "Alice"
The time span of the simulation environment 30 days. The state of user is defined as where No, is the number of days when the user receives coupon 6; in the period of 30 days, and M.y is the number of days when the user logs into the platform the next day after receiving coupon c, the day before. There are 21 items of action that represents
(Ne, Neg..... .., Nay. Mey: Mog...., Ma,)

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the value of coupons, i.c., 0.1, .... and 2.1 Yuan. The reward is defined as 0 if the user logs into the platform the next day after receiving a coupon; otherwise, it is -1. Besides, there are 21 discrete values of X: 0, 0.05, 0.1,... 0.95, 0.9.5 1.0. Appendix [.. provides all hyper-parameters of algorithms and more details about the simulation environments.
5.1.2 Evaluation Metrics
Three metrics are used to evaluate the performance of algorithms in the simulation environment. The first metric is AvgLogins, which is defined as the average of the number of days all users log to the simulation platform in one episode of 30 days. The second metric is AvgCost, which is defined as the average cost of allocating coupons to all users in one episode of 30 days. The third metric is return on investment (ROI), which is defined as the metric AvgLogins divided by the metric AvgCost. Obviously, larger values of AvgLogins and ROI and a smaller value of AvgCost indicate better performance.
5.1.3 Results
To answer question (1) in simulation environment, we compare the computation overhead of >-update based approach [20 335 and our approach in Table [ The tests are conducted in the same PC environment (Intel Core i7- 8700k CPU and a single Nvidia GeForce GTX 1080 GPU) and the termination condition of the learning process for both two methods is the same that the AvgCost is 7.0 Yuan and the AvgLogins is 15 days. Both two methods employ R-B R-BCQ as the offline RL algorithm in the experiment. As (shows, the required number of episodes for policy learning and the required training time using our approach are both significantly less than those using X-based mechanism. The results show the effectiveness of our approach in reducing the computation overhead of policy learning.
Table The overhead of X-update based mechanism [20 vs. our approach terms of the required number of episodes in policy learning and the required training time.
Method
Episodes
Time cost
A-update approach
14000
2.187h
Our approach
3000
0.439h
To answer question (2) in simulation environ- ment, we compare R-BCQ method to BCQ [3], REM [ and another model-based offline RL
REM
B02
NONO
2-11.
method: MOPO 33 Figure 3 shows the re-
sult when the value of A is O, 0.5 and 1. We first study the performance of R- RBBCQ, BCQ and REM algorithms. Recall the definition of reward function p², does not include the cost when À is O. Thus an optimal strategy must lead to the greatest cost in theory. As shown Figure [3a and Figure 3bb when À is O, R-BCQ method and REM method generate similar policies with higher AvgCost than that of BCQ method, and their AvgLogins values are also higher. This indicates that R- R-BCQ method and REM method exhibit better performance because the strategies they learned are more in accordance with the ex- pectation. Regarding the ROI, R-BCQ method exhibits a superior performance over REM and BCQ method that the ROI of R-BCQ is higher than that of REM or BCQ method in Figure 3c This result demonstrates the effectiveness of R- BCQ method that combines the advantages of REM and BCQ methods. Next, we study the performance of MOPO algorithm. Figure (3b] show that the AvgCost using MOPO method is significantly higher than that of other methods. The results illustrate MOPO method is not suit for the environment of coupons allocation. We speculate the reason for this result is that it difficult to estimate the transition and reward function in such complicated coupons allocation environment which is full of highly randomness, c.g., the
Fpudd XM0
2011
(a) The comparison results of AvgLogins
1-15
2-12
200 KM0
Fpudis
2011
(b) The comparison results of AvgCost
1-15
200
(c) The comparison results of ROI
Figure 3: We evaluate the performance of BCQ, REM and R- R-BCQ algorithms on the simulation experiments. The solid and dashed lines show the mean and standard deviation of results over five runs, respectively.
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retention information of a user depends on the user's s own preference and we can not judge whether the user will logs in the platform the next day accurately. Thus, as model-based method, MOPO may not gain desired performance in our environment. Based on above results, we consider only deploying R-BCQ, BCQ and REM methods in the e-commerce market of real world.
To answer question (3) in simulation environment, we compare REME method with IS [24]. DM B1]. DR [17] and FQE method 88 20] Results of the errors between the evaluated Q-value of AvgLogins and the real Q-value of AvgLogins are given in Table Results of the errors of evaluating AvgCost are presented in Appendix G Note that we take the learning step (Is) of evaluated policy (R-BCQ) as 1000, 2000 and 4000 and the value of À as 0. 0.5 and 1, thus there are nine cases for each OPE method. As show in T REME method achieves the least error among all methods. which illustrates its high evaluation accuracy. Besides, DM and FQE method achieves sub- sub-optimal performances, while DR and method have the worst performances. The results show the superiority of direct evaluation methods that do not require predicting the action distribution of behavior policy (More related work about the direct and non-direct evaluation methods is provided in Appendix (A.2].
Table 2: The errors between evaluated value of AvgLogins and real value of AvgLogins using different OPE methods. The value of in evaluated policy is O. 0.5 or 1, and the learning step of evaluated policy is 1000, 2000 or 4000. The bold values represent the best method with least errors.
OPF Method
Errors (Days) when À = 0
Errors (Days) when À = 0.5
Errors (Days) when À =
Is=1000
Is=2000
Is=1000
Is=1000
Is=2000
Is=4000
Is=1000
Is=2000
Is=4000
IS
3.7837
3.1353
2.1883
2.7559
2.9531
3.2068
0.4299
0,4299
0.4301
DM
0,0201
0.0204
0.0191
0.0204
0.0201
0.0195
0.0192
0.0197
0.0194
DR
1.0126
0,8014
0.5139
2.1328
2.2951
2.5462
0,2258
0.2252
0,2258
FOR
0.2064
0,1483
0.0644
0.2102
0.1844
0.1686
0.0196
0.0192
0.0193
REME
0.0135
0.0127
0.0158
0.0118
0.0085
0.0093
0.0100
0.0082
0.0091
5.1.4
Ablation Study
To answer the question (4), we show the changes of AvgLogins, AvgCost and ROI with regard to various Lagrangian variable values under the
Argaggs (Dea))
RON POR wang
2
R-BCQ method. As displayed in Figure the metries AvgCost and AvgLogins both decrease with the increase of the value of X. This result is reasonable because the greater the value of À is, the greater the weight of the cost in the reward function will be. Besides, the result verifies the Assumption introduced in Appendix B which is, the greater retention rate of users will be. Also, the index ROI increases with the value of X, which indicates that the metric AvgCost has a greater impact on ROI than AvgLogins.
Figure 4: Effect of Lagrangian variable À on the per- formance of R-BCQ algorithm in terms of AvgLogins (Left), AvgCost (Mid) and ROI (right) says that the greater the cost of distributed coupons
5.2 Real-world Experiments
5.2.1 Real-world Platform
We apply our methods in the scenario of daily check-in of Taobao Deals, which is mobile shopping app launched by Alibaba Group in 2020 with over 10 million daily active users. Each user receives a coupon when opening the app for the first time in a day. Users can use the coupon while shopping to make a subtraction of payment. Each coupon is valid for 24 hours and can be used only once. The screen views of the shopping app and the daily check-in scenario are shown in the Appendix E
We collect the real data sampled from the Taobao Deals app to create the training dataset that consists of over 2 million users' daily check-in records from January 2021 to March 2021.
The state in real environment consists of the contextual information and behavior information of user. The contextual information of a user includes the gender, age, and location, etc. The behavior information is the retention information of users in the app. just like the state we defined in the simulation environment. The action set consists of 13 items of coupons: 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05 and 1.1 Yuan. The reward is defined as if the user logs into the app the next day after receiving coupon; otherwise it is -1. The length of
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one episode is 7 days. The seven-day -ay budget for the coupon allocation per user is 4.1 Yuan. The value of ó is 0.1. Appendix F2 provides all hyper-parament of the real-world experiments environment.
5.2.2 Baselines and Evaluation Metrics
In addition to BCQ and REM methods, we compare our method with two uplift model based baselines that are currently adopted to allocate coupons in Taobao Deals: Logistics regression + Linear programming (LR+LP) [25] and Gradient boost decision tree + Linear programming (GBDT+LP) [26 [7]]. Two methods both consists of two modules: a prediction model to predict users' retention intent after receiving different coupons using LR or GBDT method and an action selection model using LP method. These two methods are proved to be able to gain promising results in the e-commerce market.
In addition to metrics AvgLogins, AvgCost and ROI, we also employ a metric ROI Imp, which is defined as the ROI improvement rate using other four methods compared to using LR+LP method.
5.2.3 Results
We first choose the policy with the value of À which makes the cost
Lambda Selection
satisfy the condition EenD' [ (s, h (s, A), A) E [b 6, b]. As shown in the Figure we choose REM policy with À = 0.25, BCQ policy with À 0.35 and R-BCQ policy with X = 0.55 as coupons allocation policies in the e-commerce platform. The results also verify that A-generalization method can scale the performance of offline RL algorithms with different values of À in question (4).
AugCost (Yuan)
RECC
Budget
To answer question (2) in real environment, we deploy all methods in Taobao Deals app for two weeks from March 9th to March 22nd. The experiments follow the online A/B testing methodology and the results are shown in Table 3 From the table, we observe when AvgCost of all methods is similar, the evaluation metrics AvgLogins and ROI of BCQ. REM and R-BCQ methods are obviously higher than those of LR+LP and GBDT methods. This result shows that offline RL methods gain superior performance over common uplift model based methods. The reason for this result is that the uplift model based method aims to maximize the benefit in one day while ignoring future benefits making decision (35). Besides, we observe that R-BCQ method gains the biggest ROI in three RL methods. This conclusion consistent with the conclusion drawn in the simulation experiments. Experimental results illustrate the effectiveness of R- B-BCQ method in increasing users' activity within the limitation of budget.
0.0
0.2
13.4
0.6
1.0
Figure 5: The results of REM, BCQ and R-BCQ methods with the value of ranging from 0 to 1
Table
The online results Taobao Special Offer Edition app during two weeks. The bold values represent the
method with the greatest AvgLogins, greatest ROI and least AvgCost.
Results in week
Results second week
Method
AvgLogins (Days)
AvgCost (Yuan)
ROI (Days/Yaan)
AvgLogins (Days)
AvgCost (Yuan)
ROI (Days/Yuan)
ROI Imp
ROT Imp
LR+LP
5.0416
4.0628
1.2409
0
$,3099
4.0684
1,3052
GBDT+LP
5.0442
4.0776
1.2371
-0.31%
S.3802
4.0756
1.3201
1.14%
BCQ 5.6832
4.0740
1,3950
12.42%
5,8789
4,0698
1.4445
10.67%
REM
5.7108
4.0644
1.4051
13.23%
5,9092
4.0729
1.4509
11.16%
R-BCQ 5.8252
4.0654
1.4329
15.447
5.9871
4.0528
1.4773
18.18%
To answer question (3) in real environment, we compare REME algorithm with IS, DM, DR and FQE evaluation methods in the online experiments, The evaluated policy is R-BCQ policy deployed in the real platform. Experimental results of the errors between the evaluated and real value of AvgLogins and the errors between the evaluated and real value of AvgCost are shown in Table 4 As shown in table, REME gains the best performance among all methods with the least evaluation errors of AvgLogins and AvgCost. Besides, we also observe that DM and FQE perform worse than REME, and IS performs worst among all methods. These results are roughly consistent with the conclusion drawn in the simulation experiments.
Table 4: The errors of REME vs. other methods when evaluating AvgLogins and AvgCost. Bold values represent the best method with the least errors.
OPE Method
Errors of AvgLogins (Days)
Erroes of AvgCost (Yuan)
IS
0.2203
0.2754
DM
0,1417
0.1923
DR
0.1848
0.1881
FQE
0.1933
0.1515
REME
0.0443
0.0221
9

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Note that the great computation overhead makes the X-update based approach cannot be deployed in the real shopping app. Thus there is no need to conduct repeated experiments to answer question (1).
6 Conclusion
In this paper, we propose a BCORLE(A) framework to solve the problem of budget constrained coupons allocation in e-commerce market. The proposed >-generalization method contributes to developing an optimal coupons allocation policy with a small computation overhead of policy learning compared with existing methods. For policy learning, we propose R-BCQ method that addresses the problem of extrapolation error and retains the strong ability of generalization of learned policy. Further, we propose a novel off- off-polic evaluation method called REME evaluate the performance of policies accurately. Experimental results obtained using simulation environment and online real-world e-commerce market verify the effectiveness of our approach.
7
Acknowledgments and Disclosure of Funding
We thank the members of the business platform of Alibaba Group and Chengwei Zhang for their insightful feedback and comments. This work was supported in part by the National Natural Science Foundation of China under Grant 61973247 and 62173268, China Postdoctoral Science Foundation 2021M692566.
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13


Reviews:
[{"review_id": "yZ5dJ2LbIC_", "reviewer": "Reviewer_gJ2K", "summary": "The paper presents a new reinforcement learning-based solution to the problem of optimal coupons allocation. The authors build upon an existing method that relaxes the constrained RL problem using lagrangian multipliers but that requires repeated full policy learning steps in the process of finding the optimal \\lambda, which can be extremely computationally expensive. To this end, the authors propose a change of formulation of the original problem to a multi-objective RL problem that learns a policy that adapts to multiple lambdas simultaneously avoiding the need to recompute the policy subsequently. In order to solve this new RL problem, the authors propose R-BCQ, which merges ideas from existing sota offline RL approaches, BCQ and REM.\nFinally, the authors propose REME, a novel evaluation method and evaluate the proposed model.", "questions": "", "limitations": "", "rating": 4, "confidence": 3, "soundness": null, "presentation": null, "contribution": null, "strengths": "", "weaknesses": "", "quality": null, "clarity": null, "significance": null, "originality": null, "strengths_and_weaknesses": "", "was_revised": false, "final_justification": "", "rebuttal": "", "claims_and_evidence": "", "methods_and_evaluation_criteria": "", "theoretical_claims": "", "experimental_designs_or_analyses": "", "relation_to_broader_scientific_literature": "", "essential_references_not_discussed": "", "other_strengths_and_weaknesses": "", "other_comments_or_suggestions": "", "questions_for_authors": "", "summary_of_paper": "", "summary_of_recommendation": "", "technical_quality": "", "clarity_of_presentation": "", "potential_impact": "", "robotics_focus": "", "quality_of_limitations": "", "questions_for_rebuttal": "", "reasons_to_accept": "", "reasons_to_reject": "", "questions_to_authors": "", "main_review": "Originality: \n* The problem is relatively new, and the approach solves a clear computational bottleneck of the previous method.  Having said that, while the \\lambda-generalisation is explained quite well with the help of Appendix C, the R-BCQ and REME algorithms are simply presented but not clearly motivated and explained. For example, the architecture of the generative model G is never presented. \n\nQuality: \n* The experiments show both on simulated and real traffic the value of each of the three components using ablation studies. \nWhile this is quite motivating, it is not clear how well the findings generalise outside of the specific problem of coupon allocation. \nOverall, I find that the the amount of complexity in the solution would requite a more extensive set of experiments that would show the larger applicability of the proposed methods, especially for R-BCQ and REME.\n\nClarity: \n* In terms of clarity I find the paper to be reasonably well-written, but due to the extensive nature of the proposed changes, some of the parts of the proposal are insufficiently covered. \n\nSignificance: \n* The results are quite relevant for the problem domain of coupon allocation but I think the paper fails to convince of the larger applicability of proposed methods, making it a better fit for a more applied conference, where the performance of the application is more important than the generality of the proposed methods.", "summary_of_the_paper": "", "summary_of_the_review": "", "strength_and_weaknesses": "", "limitations_and_societal_impact": "NA", "review_text": "", "extra_scores": {"ethical_concerns": "NA", "needs_ethics_review": "No", "ethics_review_area": "", "time_spent_reviewing": "2hrs"}, "extra_text": {}}, {"review_id": "AXn_o4eiot", "reviewer": "Reviewer_34tS", "summary": "The authors proposed an offline reinforcement learning framework for coupons allocation within a fixed budget. Existing methods formulated this problem as a Lagrangian dual problem and solved it with reinforcement learning. These methods caused great computation overhead and a huge policy space. To make up for these shortcomings, the authors proposed an offline reinforcement learning framework consisting of a lambda generalization method, an offline RL algorithm R-BCQ, and a model-free metric. The lambda-generalization method learns a suitable lambda during reinforcement learning process. Besides, R-BCQ combines the advantages of two popular models and achieves good results.  Finally, extensive experiments have been done to prove the effectiveness of this offline reinforcement learning framework. \n", "questions": "", "limitations": "", "rating": 5, "confidence": 4, "soundness": null, "presentation": null, "contribution": null, "strengths": "", "weaknesses": "", "quality": null, "clarity": null, "significance": null, "originality": null, "strengths_and_weaknesses": "", "was_revised": false, "final_justification": "", "rebuttal": "", "claims_and_evidence": "", "methods_and_evaluation_criteria": "", "theoretical_claims": "", "experimental_designs_or_analyses": "", "relation_to_broader_scientific_literature": "", "essential_references_not_discussed": "", "other_strengths_and_weaknesses": "", "other_comments_or_suggestions": "", "questions_for_authors": "", "summary_of_paper": "", "summary_of_recommendation": "", "technical_quality": "", "clarity_of_presentation": "", "potential_impact": "", "robotics_focus": "", "quality_of_limitations": "", "questions_for_rebuttal": "", "reasons_to_accept": "", "reasons_to_reject": "", "questions_to_authors": "", "main_review": "Originality: The authors considered a practical problem, Coupons Allocation. To solve this problem, they proposed a framework consisting of a pre-processing method, a combination of two popular models and a metric. \n1.\tThe technical contribution of this paper seems incremental. The framework is more likely to three tricks instead of a unified framework. Specifically, lambda-generalization method is designed for time efficiency, R-BCQ is designed for accuracy and REME is a newly-proposed metric.  Also, R-BCQ is only a combination of two popular models. \n2.\tAllocating coupons for users is not only to retain users but also to stimulate consumption. It is not reasonable to only treat user retention as a reward.\n\nQuality: \n1.\tExperimental results cannot prove the effectiveness of the framework. Specifically, my primary concern is about the lambda generation method. In the abstract section, ``lambda-generalization method is proposed to lead the policy learning process can be executed according to different lambda values adaptively''. However, no experimental results can prove it. \nAs shown in subsection 4.1 and Appendix C, lambda should be a range according to the reward and the cost. However, experimental results are mostly based on the fixed lambda. E.g., \n(1)\tAs shown in Table 2 and Figure 3, results are based on the fixed lambda (lambda = 0/0.5/1.0). Obviously, these results based on the fixed lambda cannot prove the effectiveness of lambda generalization. \n(2)\tIn Table 3, R-BCQ is also based on the fixed lambda. As shown in line 359-361, ``we choose REMpolicy with lambda = 0.25, BCQ policy with lambda = 0.35 and R-BCQ policy with lambda = 0.55 as coupons allocation policies in the e-commerce platform. ''\n2.\tAs shown in Table 1, spent time was used to compare time efficiency among different models. Obviously, spent time can be very different based on different implementations. Time complexity and space complexity are better metrics for this situation. \n\nClarity: \nThis paper is not well-written. E.g., \n1. The studied problem is not apparent. In the abstract section, the authors mentioned several issues, such as ``allocate coupons within a fixed budget while maximizing users' retention on the e-commerce platform'', ``existing studied with a huge computation overhead'', and ``the requirements changes rapidly in the real world''. The authors overlook too many details. \n2. The comparsions between two popular methods (BCQ and REM) are not clearly introduced. \n3. I don’t think a unified framework has been introduced. The summarized contributions are not accurate enough. \n\nSignificance: \n1. The experimental results proved the effectiveness of the proposed model, R-BCQ, and the model-free metric, REME. However, the effectiveness of lambda generation method wasn’t verified experimentally. Please refer to ``Quality'' for more details. \n2. We don’t think that most researchers can follow this work because data on real platform will probably not be open. We also check the submitted codes but do not find such data. \n", "summary_of_the_paper": "", "summary_of_the_review": "", "strength_and_weaknesses": "", "limitations_and_societal_impact": "As the authors mentioned in section 5.2, each coupon is valid for 24 hours; if the users don't use the coupons, the e-commerce platform has no cost. Do the authors consider such a situation?\nThe simulation environment setup is not reasonable, as the real-world environment is super complicated. It is meaningless to conduct experiments in the simulation environment.\n", "review_text": "", "extra_scores": {"ethical_concerns": " The users' age and gender should be used to train the model as it violates the user's privacy information. ", "needs_ethics_review": "No", "ethics_review_area": "", "time_spent_reviewing": "6"}, "extra_text": {}}, {"review_id": "8p8Tz-wX-sG", "reviewer": "Reviewer_XKos", "summary": "This paper proposed a budget-constrained offline RL framework to solve the CMDP problem of coupons allocation in an e-commerce platform. More specifically, how to allocate coupons within a fixed budget while maximizing users’ retention on the platform. This is an action-constrained MDP problem commonly formulated as a Lagrangian problem. The authors further transformed the lagrangian problem into an RL one by subtracting the cost from the reward function.\n\nInspired by multi-objective RL, they extended \\lambda into the transition tuple and augmented the training dataset under different values of \\lambda. Thus avoiding re-learning the policy as \\lamda changes. \n\nFor the offline RL algorithm, the authors combined BCQ and REM to train a policy. To evaluate the learned policy, they further trained a multi-head evaluation network.\n\n", "questions": "", "limitations": "", "rating": 6, "confidence": 3, "soundness": null, "presentation": null, "contribution": null, "strengths": "", "weaknesses": "", "quality": null, "clarity": null, "significance": null, "originality": null, "strengths_and_weaknesses": "", "was_revised": false, "final_justification": "", "rebuttal": "", "claims_and_evidence": "", "methods_and_evaluation_criteria": "", "theoretical_claims": "", "experimental_designs_or_analyses": "", "relation_to_broader_scientific_literature": "", "essential_references_not_discussed": "", "other_strengths_and_weaknesses": "", "other_comments_or_suggestions": "", "questions_for_authors": "", "summary_of_paper": "", "summary_of_recommendation": "", "technical_quality": "", "clarity_of_presentation": "", "potential_impact": "", "robotics_focus": "", "quality_of_limitations": "", "questions_for_rebuttal": "", "reasons_to_accept": "", "reasons_to_reject": "", "questions_to_authors": "", "main_review": "To the best of my knowledge, the paper proposes a novel problem formulation and method. It would be better if more related work would be added and included in the main paper and not supplementary materials. \n\nThe paper is very well written and easy to follow. The poofs of the claims are all included. \n\nThe \\lambda generalization technique clearly reduced the computational overhead. But the paper lacks a comparison to the most recent SOTA in offline RL like CQL. In the metric defined by the authors, the experiments show that R-BCQ works better than BCQ and better than REM in the ROI metric. Moreover, adding a justification for their representation of states would be good.", "summary_of_the_paper": "", "summary_of_the_review": "", "strength_and_weaknesses": "", "limitations_and_societal_impact": "The authors adequately addressed the social impacts. ", "review_text": "", "extra_scores": {"needs_ethics_review": "No", "ethics_review_area": "", "time_spent_reviewing": "5"}, "extra_text": {}}, {"review_id": "6uR1rdnyBQI", "reviewer": "Reviewer_1JJe", "summary": "This paper presents a budget constrained offline reinforcement learning and evaluation framework for the coupon allocation problem on e-commerce platforms. The proposed framework leverages the lambda-generalization technique to avoid retraining thus significantly reducing the computation overhead. The proposed framework was also evaluated via both simulated environment as well as real-world a/b testing.", "questions": "", "limitations": "", "rating": 7, "confidence": 3, "soundness": null, "presentation": null, "contribution": null, "strengths": "", "weaknesses": "", "quality": null, "clarity": null, "significance": null, "originality": null, "strengths_and_weaknesses": "", "was_revised": false, "final_justification": "", "rebuttal": "", "claims_and_evidence": "", "methods_and_evaluation_criteria": "", "theoretical_claims": "", "experimental_designs_or_analyses": "", "relation_to_broader_scientific_literature": "", "essential_references_not_discussed": "", "other_strengths_and_weaknesses": "", "other_comments_or_suggestions": "", "questions_for_authors": "", "summary_of_paper": "", "summary_of_recommendation": "", "technical_quality": "", "clarity_of_presentation": "", "potential_impact": "", "robotics_focus": "", "quality_of_limitations": "", "questions_for_rebuttal": "", "reasons_to_accept": "", "reasons_to_reject": "", "questions_to_authors": "", "main_review": "Strength:\n\n- Automating coupon allocation is an important problem on today's large-scale e-commerce marketplaces.\n\n- The proposed framework is technically well-motivated, including the R-BCQ method for policy learning, REME for off-policy evaluation, and the lambda-generalization method to avoid retraining - more importantly, it’s also very practical, where the comparison in Fig 2 is a good example to demonstrate its value on this front.\n\n- The proposed framework was also tested in both simulated environment as well as real-world experiments - both demonstrates its effectiveness against several baselines. \n\nWeakness:\n\n- I find the Constrained MDP (CMDP) framing as well as its policy learning/evaluation strategies intuitive, but will leave the judgement of its technical contributions to other CMDP experts. \n\n- Related work can be expanded beyond discussions around CMDP, where some off-policy methods and other existing studies for the coupon allocation problem may need to be discussed.\n\nOverall I find the work well-motivated and the paper is interesting to read. I also very appreciate the authors provided real-world experimentation results, which is a big plus to validate its effectiveness.", "summary_of_the_paper": "", "summary_of_the_review": "", "strength_and_weaknesses": "", "limitations_and_societal_impact": "One limitation of the current draft is it seems constrained on the off-policy RL scope and didn't discuss much about the general coupon allocation/optimization problem. \n\nTo be clear I find the framing in the current paper is acceptable. Customized coupon delivery (more generally price discrimination) makes sense in the rational economics world but may have societal impact, depends on how these promotions are communicated and how consumers perceive the promotions. Therefore adding a few sentences in the introduction on this front might be helpful to clear potential concerns.", "review_text": "", "extra_scores": {"needs_ethics_review": "No", "ethics_review_area": "", "time_spent_reviewing": "4"}, "extra_text": {}}]

Author rebuttal:

Meta-review: This paper received mixed reviews from the reviewers. Its strength is that it seems successful in proposing a budget constrained offline reinforcement learning and evaluation framework for the coupon allocation problem on e-commerce platforms. The drawbacks of the paper are the limited novelty of the approach (it appears to combine/unify several prior methods) and the specificity of the application. Given that there is no evidence of wider applicability of the proposed method, I recommend rejecting this paper for NeurIPS. However, the authors are encouraged to submit the manuscript to a more applied venue.
Decision: Accept (Poster)