1 Introduction
In this paper, we consider a two-stage supply chain facing a pricing-discount dependent demand, which is sequent to Petruzzi and Dada
[1] whose model facing a pricing-dependent demand. This scenario occurred in two stages. In stage 1, the supplier reserves a certain capacity accordingly to the historic demand data. After some leadtime stage 2 arrives, the manager updates the supply chain based on the new information, the supplier offers a wholesale price to retailer and the retailer makes an order quantity to the supplier and a selling price discount to market. We suppose that, for retailer, the unmet demand is lost, the unsold items are salvaged, for supplier the unused portion of the reserved capacity is salvaged. We make optimal decisions on the reserved capacity in stage 1, selling price discount and order quantity in stage 2.
Pricing-discount occurred between buying and selling parties is the preferential privilege in commodity procurement. It is often used in group-buying strategy. Group-buying, as a new mechanism for selling through social interactions, has generated increasing attention in recent years due to the simplification of the information and communication technologies. The group-buying model can be looked as a generalization of the classical newsvendor model which is from the market with random situation, such as random information and random demand, see Dvoretzky, et al.
[2] and Scarf
[3]. The group-buying has a history that has been traced back to 1990s (see, e.g., Anand and Aron
[4]), when the internet-based group-buying is being wildly used for both business-to-business (B2B) and business-to-consumer (B2C) transaction. In some industries such as food services and health care, group-buying organizations have a dominate presence, see Hu
[5]. In the scenario of group purchasing, how to develop the optimal discount strategy becomes a key issue which affects the profits of sellers, see Dolan
[6]. There is little work on the group-buying, Luo and Wang
[7] regard a group-buying as a promotion way and consider the group-buying's impact on the sellers. Taking it into account that the seasonal epidemic goods are developing and the life cycle of most products is constantly shortened, the authors introduce traditional newsvender model framework.
Two-stage supply chain model is basic model in management science, and captures researcher's interest in recent years. Barnes-Schuster, et al.
[8] deals with a two-stage correlated demand model, in which the buyer purchases an option besides placing a firm order at the start. After the demand is realized in the first stage, the buyer can partly execute the option to satisfy the demand in the second phase. Mathur and Shah
[9] also consider a two-stage supply chain coordination problem, in which the supplier decides the production quantity before the demand is realized. Mathur and Shah propose to apply the contract with two-way penalties to coordinate the supply chain. Conditions of the contract for achieving supply chain coordination are derived separately for the cases when demand follows an uniform distribution and when production capacity is jointly decided by both parties of the supply chain. Chen, et al.
[10] consider a scenario where the supplier reserves production capacity for the retailer in advance, and permits the retailer to place an order not exceeding the reserved capacity after a demand information update during a lead-time. They formulate a two-stage optimization problem in which the supplier decides the amount of capacity reservation in the first stage, and the retailer determines the order quantity and the retail price after observing the demand information in the second stage. However they do not consider a group-buying strategy.
In this paper, we construct a centralized supply chain together with two characteristics of pricing-discount and two-stage based on the situation of selling a seasonal product. Our work is based on previous work and generalizes it. We consider a two-stage supply chain where, at the beginning of stage 1, the supplier reserves production capacity based on historic data in advance, stage 2 comes to us after some leadtime, both the supplier and the retailer update the demand information, the retailer then places an order not exceeding the reserved capacity based on the selling-pricing discount dependent demand. What should be pointed out is our model's exclusive feature: In our model, the retail price is fixed and the demand function becomes a function of price discount. We make optimal decisions on the reserved capacity in stage 1, selling price discount and order quantity in stage 2. The rest of the paper is organized as follows. In Section 2, we describe the model in details, including the basic assumptions and the decision structures. In Section 3, we make optimal decisions on the reserved capacity in stage 1, selling price discount and order quantity in stage 2. We first analyze stage 2 and then stage 1. We give a numerical example to explain the optimal decisions obtained in Section 3. In Section 4, we make conclusions.
2 Model Description
The supply chain operates in two stages. At stage 1, that is, at the very beginning of the model, the supplier reserves a certain capacity accordingly to the historic demand data. Stage 2 comes to us after some leadtime, based on the new information the manager updates the supply chain, the supplier offers a wholesale price to retailer and the retailer makes an order quantity to the supplier and a selling price discount to market. The demand occurs at the end of stage 2. We suppose that, for retailer, the unmet demand is lost, the unsold items are salvaged, for supplier the unused portion of the reserved capacity is salvaged.
2.1 The Demand Function
In this paper, we assume that the demand function is in the additive form, and is a function of selling price discount, that is,
where is the price discount parameter with its value assumed to be in . is the increasing part of the demand due to the price discount. is the demand when there is no price discount. We claim , because there is no discount when , and then . For the increasing part of the demand , we adopt a linear equation:
where is the impact factor of the demand due to the price discount, represents the elastic coefficient of the demand responsiveness to the selling price discount, is a parameter and satisfies . This implies that the demand function have the following form:
We give more information for the parameter and . For parameter , in stage , is thought as a positive random variable, because, in generally, is unknown prior to the selling season when the capacity reservation is made. However, after a leadtime, stage is entered, in which the newsvendor model updates the demand forecast based on some new information, then is realized. Thus, there are two aspects of the demand uncertainty in our model, that is, (in stage ) and . We suppose that it is distributed in the range with a cumulative distribution function (c.d.f.) and its corresponding probability density function (p.d.f.) . The random variable lies in the interval with c.d.f. , p.d.f. and the mean .
2.2 Notations
The needed cost notations are summarized as follows:
: The reserved capacity of the supplier;
: The retailer's order quantity to the supplier;
: Per unit cost of the reserved capacity in stage ;
: Per unit salvage value of the unused capacity, i.e., the part committed in stage but not actually used for production;
: Per unit product cost in stage ;
: Per unit salvage value of the leftover inventory at the end of the selling season;
: Per unit penalty cost of stock-out;
: The constant selling price to customer.
2.3 Assumptions
To operate the model more reasonable, we need the following assumptions:
1) , it means that the reserved capacity cost is larger than the salvage value of the unused capacity.
2) is a constant value.
3) The random variable and are assumed to be independent for convenience.
4) or the retailer will order much more products to extend his profit.
5) .
6) , it guarantees .
7) The hazard rate of satisfies:
3 The Optimal Decision for Supply Chain
In this section, we will study the optimal decision in two steps: Stage and stage . We first go to stage , and then stage . In stage , we will determine the optimal selling price discount and order quantity based on constant . Then in stage , we will make the optimal decision on the capacity based on random variable .
3.1 The Retailer's Optimal Pricing Discount and Ordering in Stage
In stage , we go to find the optimal decision for the selling price discount and ordering quantity of the retailer. At the beginning of stage , is thought as a positive constant, denoted by , and the demand function is then updated to
where denotes the deterministic part of the demand function. In the following, we first give the profit functions for given capacity . Let be the profit function when the reserved capacity is enough to satisfy the order quantity, that is, ; and be the profit function when the reserved capacity is not enough to satisfy the order quantity, that is, . For case , the retailer orders a quantity , however, the supplier provides only. In this way, it says that the system just determines the optimal selling price discount, which is independent to the order quantity. So, is degenerated into a univariate function and denoted by . The profit functions are: When ,
and when ,
where and for any members and .
Next, we will discuss the above two profit functions and make the optimal decision respectively. First we will discuss the case of , and then .
For case
, for the convenience of analysis, we define the following safety stocking factor, see Petruzzi and Dada
[1],
We rewrite the profit function as
Taking expectation with respect to we have
Where
Next we give the optimal and . Before doing this, we first present a Lemma in the following, which show us the optimal for any given .
Lemma 1 Suppose that there is no capacity constraint at the beginning of stage . is concave in for any given , the optimal price discount is a unique function of satisfies the following:
where
is the optimal price discount in the absence of uncertainty.
Proof Deriving the first-order and the second-order partial derivatives of in , we get
Since in stage , it follows that
That is, is strictly concave in . So, has a unique optimal solution for any given . Let , we get . Then Lemma is proved.
Remark 1 The optimal price discount
without uncertainty, in Lemma
, appeared in [
7,
9], readers can refer to them for details.
Based on Lemma , we can get the optimal in the following Lemma .
Lemma 2 Suppose that the demand takes the form in stage . If there is no capacity constraint, then the optimal stocking and pricing discount policy is to stock units with the unit price discount , where is specified by Lemma and is the optimal solution that satisfies:
Proof Deriving the first order derivative of in , we get
where the second equality holds because by Lemma . To identify values of that satisfy the above first-order optimality condition, let
and consider the zeros of :
where
Also,
Because is a distribution satisfying the condition , then, it follows that is unimodal or monotonous. So, has at most two roots. Further,
and
so, has only one root, it indicates that has a change from positive to negative. Therefore, has only one unique value that satisfies , i.e.,
Then, we get the result.
Remark 2 Be similar with Theorem
in [
7] or Theorem
in [
9], we can claim that
is unimodal in
if
. Thus, there is a unique solution to
. Note that the solution exists for
. Substituting
into
, we can get the optimal price discount
.
Lemma 3 If
then, , which means that there is no need price discount, in words, ; if
then, , which means that one can sell product at a optimal price discount .
Proof The proof is directly from in Lemma , and the proof is omitted.
Next, we consider the case . In this case, the reserved capacity is insufficient to warrant the optimal order quantity in stage , then the system just determines the optimal price discount to run out the reserved capacity, i.e., . So, the expected profit function is a univariate function in , its expectation with respect to gives:
Lemma 4 For the case , that is, the reserved capacity is less than the optimal order quantity, then the system is optimized by ordering and selling discount at , where is the unique solution of the following equation
Proof Taking the first and second derivatives of , we have
which means is concave with respect to the selling price discount of . Letting , then we get the result.
3.2 Capacity Reservation Strategy in Stage
At the very beginning of stage , the manager needs to determine the reserved capacity facing an uncertain market. We do this decision based on the discussion in the above subsection, that is, the cases and . However, we noted that, in stage , the parameter in is thought to be a positive random variable.
Let
which represents the optimal order quantity in stage 2 when the capacity is not constrained. Note that is continuous in , so there exist maximum and minimum in the range of , denoted by and respectively. Let , this implies that , where
Let be the total profit function, its expected value is
Taking expectation with respect to , we get the expected profit function
Where and are the optimal profit in stage fore cases and respectively. We assume that the reserved capacity satisfies . From Lemma , we know, if one can sell product at an optimal price discount , the condition must be true, that is, the product can sold with the optimal discount . So, if , the cumulative distribution function . To avoid trivial cases, we assume .
Next, we give the optimal reserved capacity.
Theorem 1 The optimal reserved capacity, denoted by , is the unique solution to the equation
where
Proof We note that when
the optimal and can be taken. It is equal to the capacity constraint is unbound. On the other hand, when
the optimal can not be taken. It is equal to the capacity constraint is bound. In fact, there are three possible cases.
The first case: . In this case, when the capacity constraint is unbound, for any given , can satisfy the maximum . We maximize the objective function:
where is the maximum expected profit in stage . Since
the optimal capacity is the lower limit of this range, that is, .
The second case: . In this case, when the capacity constraint is bound, can not satisfy the minimum . We maximize the objective function:
where is the maximum expected profit in stage . So the optimal order quantity in stage 2 is .
The third case: . In this case, we maximize the objective function
Taking the derivative of with respect to , we can get
Since when , we have , Then
This leads to
and
So, we can get
and
Therefore, is concave in when is in the interval . Hence, the optimal capacity to be reserved in stage is the unique solution to .
When the optimal reserved capacity is determined in stage 1, the expected profit is given as well.
Example 1 We take an example to illustrate the underlying managerial insight. Consider the following problem setting in the numerical study:
We assume that the respective distributions of and are taken as uniform. With this date, we would like to see how the impact factor of the demand, , affects the optimal price discount , the optimal order quantity and the safety stocking .
As can be seen in Table 1, we can get that is increasing in , and are decreasing in . This shows that the retailer will order much more and then set a lower selling price discount, when the impact factor of the demand becomes bigger.
Table 1 Effects of impact factor of the demand |
| | | | |
50 | 0.8478 | 53.3896 | 45.7796 | 55.5698 |
60 | 0.7979 | 57.6713 | 45.5453 | 59.8255 |
70 | 0.7624 | 61.9936 | 45.3616 | 64.0951 |
80 | 0.7357 | 66.3577 | 45.2137 | 68.4018 |
100 | 0.6484 | 80.1502 | 44.9902 | 85.2638 |
4 Conclusions
In this paper, we investigate a simple centralized supply chain that sells a seasonal product with selling price-discount strategy. At the beginning of the selling season, the supplier needs to reserve capacity, which leads to a meaningful leadtime. There is an opportunity for adjusting the production after demand information updating during the leadtime. The supply chain faces a two-stage strategy problem: firstly the supplier reserves an amount of capacity; secondly the retailer decides the order quantity and the selling price discount. It is especially significant in the business of group-buying. We make optimal decisions on the reserved capacity in stage 1, selling price discount and order quantity in stage 2, we also give a numerical example to present some insights after the optimal decisions is obtained.
{{custom_sec.title}}
{{custom_sec.title}}
{{custom_sec.content}}