# Dynamic Vehicle Scheduling for Working Service Network with Dual Demands

Authors: Bing Li; Wei Xu; Hua Xuan; Chunqiu Xu
Journal: Journal of Advanced Transportation
 (2017)

---

## Abstract

This study aims to develop some models to aid in making decisions on the combined fleet size and vehicle assignment in working service network where the demands include two types (minimum demands and maximum demands), and vehicles themselves can act like a facility to provide services when they are stationary at one location. This type of problem is named as the dynamic working vehicle scheduling with dual demands (DWVS-DD) and formulated as a mixed integer programming (MIP). Instead of a large integer program, the problem is decomposed into small local problems that are guided by preset control parameters. The approach for preset control parameters is given. By introducing them into the MIP formulation, the model is reformulated as a piecewise form. Further, a piecewise method by updating preset control parameters is proposed for solving the reformulated model. Numerical experiments show that the proposed method produces better solution within reasonable computing time.


---

## Body

## 1. Introduction

The vehicle scheduling problems arise when owners and operators of transportation systems must manage a fleet of vehicles over space and time to serve current and forecasted demands.The capacity of a transportation system is directly related to the number of available vehicles. Determining the optimal number of vehicles for a transportation system requires a tradeoff among the benefits for meeting demands, the ownership costs of the vehicles, and the penalty costs associated with not meeting some demands. Serving demand results in the relocation of vehicles. Each vehicle is in a particular location, and each task demand requires a vehicle in a particular location. The assignment of a vehicle to a task demand generates revenue. Thus, we consider the problem of vehicles assignment strategy.The interaction between fleet sizing decisions and vehicle assignment decisions is the focus of this paper. There is a substantial history of research on vehicle assignment problems with fixed vehicle fleet. But the research described in this paper attempts to integrate vehicle fleet sizing decisions with vehicle assignment decisions.In this paper, we consider the dynamic vehicle scheduling for working service network with dual demands by applying an optimization modeling approach, in which the service demand in each terminal includes two type, that is, minimum demands and maximum demands. We name this type of problem as the dynamic working vehicle scheduling with dual demands (DWVS-DD). The objective is to optimize the performance of the transportation system over the entire planning horizon. The model of problem starts with the classical mixed integer programming formulation and is then reformulated as a piecewise form. We develop two types of reformulated models for the issue and present a piecewise method by updating preset control parameters.In addition to the integration of the vehicle fleet sizing and the vehicle assignment problem, two other factors, such as the working service network and working vehicle, increase significantly the complexity of the research in this paper.First, we must recognize one crucial characteristic of working service network: at any location of working service network in space and time, the demands include two types, that is, minimum demands and maximum demands. The minimum demands must be met, but maximum demands are not. If insufficient vehicles are available to meet maximum demand, the penalty cost for unmet demand will generate. This characteristic is the cornerstones of the model developed in this paper.Second, vehicles usually provide pickup or delivery services between various locations in previous studies. However, in reality, vehicles themselves can sometimes act like a facility to provide real-time services when they are stationary at one location. The vehicles cannot provide services when they are in motion, and the service begins when a vehicle arrives at a location and ends when it departs. For instance, medical treatment vehicles provide first aid services to areas where the established medical facility is temporarily insufficient. Also, food trucks provide fast food services in different regions in different time periods of the day. Note that when these vehicles are in service, they behave like traditional facilities. The term working vehicle (WV) will be used in this paper to denote this vehicle. Applications of problems arise in many settings, ranging from managing emergency vehicles, medical testing vehicles, traveling salesman, and military force deployment.Overall, the objectives of this research are twofold. The first objective is to develop a novel mathematical model of DWVS-DD. In conventional mathematical models, the problem has been formulated as a mixed integer programming model. In the proposed model, the problem is reformulated as a piecewise form to find the local problem at every time period. The second objective is to propose an efficient methodology for solving the model. Specifically, the contributions of this paper are as follows:(1)
We develop the mixed integer programming model (MIP). The model then is reformulated as two novel formulations, that is, reconstruction model with single preset incremental parameters (RM-SPIP) and reconstruction model with double preset incremental-decremental parameters (RM-DPIDP).(2)
We propose the coupled correlation model of total profit, vehicle supply, minimum demand, and maximum demand. The acquisition approaches of single preset control parameters are given. Meanwhile, we propose the coupled correlation model of the revenue, penalty cost, vehicle supply, minimum demand, and maximum demand. The acquisition approaches of double preset control parameters are given.(3)
According to the specific structure of the two reconstruction models, the piecewise method by updating preset control parameters (PM-PCP) is developed.(4)
We tested the performance of PM-PCP approach by solving many instances. We compared the quality of the solutions provided by PM-PCP solving RM-SPIP and RM-DPIDP versus the results of the CPLEX solving MIP. According to our results, in most of the instances, our PM-PCP approach has a better performance. Indeed, PM-PCP provides many optimal solutions in a very short computation time.The remainder of this paper is organized as follows. Section2 of this paper discusses related earlier research efforts. Section 3 is devoted to the mathematical description of the DWVS-DD. In Section 4, we set up the problem as the classical mathematical programming formulation and present then the reformulated models. Section 5 explains the acquisition methodology of preset control parameters, based on coupled correlation function. We introduce piecewise method by updating preset parameters (PM-PCP) for solving reconstruction model in Section 6. The computational experiments are described in Section 7, and the effectiveness of the proposed method is shown from the computational results. The last section concludes with a summary of current work and extensions.


## 2. Literature Review

In this section, we review the relevant literatures about vehicle scheduling problems. Literature review indicates that vehicle scheduling problems can be divided into three groups, that is, vehicle routing, fleet sizing, and fleet assignment. The focus of our literature review will primarily be on the model and exact approach since it is also the model and approach we have taken in this paper.In recent years, many researches on vehicle routing optimization have been carried out. Hou et al. [1] focused on vehicle routing problem with soft time window constraint. An exact algorithm based on set partition was proposed to solve the balancing the vehicle number and customer satisfaction by Cao et al. [2]. Li et al. [3] studied the integrated problem with truck scheduling and storage allocation. It was formulated as an integer programming model to minimize makespan of the whole discharging course and solved by a two stages tabu search algorithm. Dabia et al. [4] presented a branch and price algorithm for time-dependent vehicle routing problem with time windows. Han et al. [5] considered a vehicle routing problem with uncertain travel times in which a penalty is incurred for each vehicle that exceeds a given time limit and given robust scenario approach for the vehicle routing problem. Muter et al. [6] proposed a column generation algorithm for the multidepot vehicle routing problem with interdepot routes. Vidal et al. [7] proposed a unified hybrid genetic search metaheuristic algorithm to solve multiattribute vehicle routing problems. Battarra et al. [8] presented new exact algorithms for the clustered vehicle routing problem (CluVRP) and provided two exact algorithms for the problem that is a branch and cut as well as a branch and cut and price.Fleet sizing is one of the most important decisions as it is a major fixed investment for starting any business. Many scholars have conducted the numerous basic studies on fleet sizing problem (FSP). Zak et al. studied a fleet sizing problem in a road freight transportation company with heterogeneous fleet [9]. Additionally, the mathematical model of the decision problem was formulated in terms of multiple objective mathematical programming based on queuing theory. A fleet sizing problem arising in anchor handling operations related to movement of offshore mobile units is presented by Shyshou et al. [10]. A simulation-based prototype was proposed and the simulation model was implemented in Arena 9.0 (a simulation software package developed by Rockwell Software). Rahimi-Vahed et al. [11] addressed the problem of determining the optimal fleet size for three vehicle routing problems, that is, multidepot VRP, periodic VRP, and multidepot periodic VRP. And a new Modular Heuristic Algorithm (MHA) was proposed. Ertogral et al. [12] explored a real strategic fleet sizing problem for a furniture and home accessory distributor. Then, a mixed integer linear program was proposed to determine the total number and types of owned and rented vehicles for each region under seasonal demand. The study developed an analytical model for the joint LGV (Laser Guided Vehicles) fleet sizing problem, also taking into consideration stochastic phenomena and queuing implications in Ferrara et al. [13]. Chang et al. [14] studied the vehicle fleet sizing problem in semiconductor manufacturing and proposed a formulation and solution method, called Simulation Sequential Metamodeling (SSM). By using an agent-based model of a flexible carsharing system, Barrios and Godier [15] explored the trade-offs between fleet size and hired vehicle redistributors, with the objective of maximizing the demand level that can be satisfactorily served. Koç et al. [16] introduced the fleet size and mix location-routing problem with time windows and developed a powerful hybrid evolutionary search algorithm. Park and Kim [17] addressed the fleet sizing of containers and developed an analytical model for the minimum container fleet size.Moreover, some literatures on fleet assignment were addressed from the viewpoint of optimization models and solution methods. Xia et al. [18] studied a comprehensive model that addresses fleet deployment, speed optimization, and cargo allocation jointly, so as to maximize total profits at the strategic level. Pita et al. [19] presented a flight scheduling and fleet assignment optimization model and carried out a welfare analysis of the network. And the optimization model and subsequent welfare analysis were applied to the PSO network of Norway. Pilla et al. [20] developed a two-stage stochastic programming framework to the fleet assignment model and presented the L-shaped method to solve the two-stage stochastic programming problems. Liang and Chaovalitwongse [21] presented a network-based mixed integer linear programming formulation for the aircraft maintenance with the weekly fleet assignment and developed a diving heuristic approach. Sherali et al. [22] proposed a model that integrates certain aspects of the schedule design fleet assignment and aircraft-routing process and designed Benders’s decomposition-based method. The liner shipping fleet repositioning problem (LSFRP) was formulated as a novel mathematical model and a simulated annealing algorithm is proposed for the LSFRP by Tierney et al. [23]. Hashemi and Sattarvand [24] studied the different management systems of the open pit mining equipment including nondispatching, dispatching, and blending solutions for the Sungun copper mine. A dispatching simulation model with the objective function of minimizing truck waiting times had been developed. A Markov decision model is developed to study the vehicle allocation control problem in the automated material handling system (AMHS) in semiconductor manufacturing by Lin et al. [25]. Simão et al. [26] developed a model for large-scale fleet management and presented an approximate dynamic programming to solve dynamic programs with extremely high-dimensional state variables. Topaloglu and Powell [27] reported how to coordinate the decisions on pricing and fleet assignment of a freight carrier. And a tractable method to obtain sample path-based directional derivatives of the objective function with respect to the prices was presented. Aimed at the stochastic dynamic fleet scheduling, Li et al. [28–30] further proposed some heuristic approaches to deal with these problems. A new and improved Lipschitz optimization algorithm to obtain a Ε-optimal solution for solving the transportation fleet maintenance-scheduling problem is proposed by Yao and Huang [31]. In this study, a procedure based on slope-checking and step-size comparison mechanisms was given to improve the computation efficiency of the Evtushenko algorithm.The focus of this paper is development of some models to aid in making decisions on the combined fleet size and vehicle assignment in working service network where the demands include two types (minimum demands and maximum demands), and vehicles themselves can act like a facility to provide services when they are stationary at one location. Two types of preset control parameters are applied to the model of the DWVS-DD so that the problem is decoupled into some local problems for different time periods. Further, a piecewise method by updating preset control parameters is proposed for solving the model.


## 3. Problem Formulation

### 3.1. Problem Description

LetG represent working service network. V is the set of working service station set in the network G. We assume that time is divided into a set of discrete time periods T={t∣t=1,…,M} where M is the length of the planning horizon. We also assume that there exist demands for vehicle work service at terminal i, i∈V, in period t, t∈T. When vehicles serve demands, the revenues will generate. We assume a unit revenue per served demand in period t, denoted as at. Serving demand results in the relocation of vehicles between various locations. It implies the need for redistribution of vehicles over the working service network from locations at which they have become idle to locations at which they can be reused. The minimum demands and maximum demands can be, respectively, represented as Qitmin and Qitmax at terminal i in period t. These demands induce vehicles available to serve them. The minimum demands Qitmin must be met, but maximum demands Qitmax are not. If insufficient vehicles are available at location i in period t to meet maximum demand, the penalty cost for unmet demand will generate. We denote the unit penalty cost per period for unmet demand by bt. The level of demand in units of vehicle loads is assumed to be specified as data. We consider ξ to be these demands which can be serviced by one vehicle. Let djk be the distance between any pair of terminal j and k. The demand of terminal k can be covered by vehicles located in j if only the distance djk≤D, where D is the maximum coverage distance. Considering the expense of purchasing or renting vehicle, we assume that the fixed costs of using vehicles are constant and denoted by c for using one vehicle. The main purpose of the DWVS-DD is to propose working vehicle assignment plan for serving as many demands as possible in the given planning horizon at the highest possible profit. Owning or leasing a fleet of vehicles is generally quite costly, so it is natural to try to optimize the size of the required fleet. We emphasize the tradeoff among the investment for establishing a suitable fleet (i.e., the fixed cost), the benefits for meeting demands (i.e., the revenue for serving demands), and the loss of benefits for failing to satisfy demands (i.e., the penalty cost for unmet demands). Dynamic working service network with dual demands is shown in Figure 1.Figure 1
Dynamic working service network with dual demands.


### 3.2. Problem Definition and Notation

We assume that planning horizon is divided into a set of discrete instantsT={t∣t=1,…,M} where M is the length of the planning horizon. A network is represented by graph G=(V,E) where V is the set of terminal. E is the set of link in the network. We present the complete notation for the problem here.Quickly summarizing the notation, we have the following decision variables:xijt is the number of working vehicles dispatched from terminal i to terminal j in period t, i,j∈N, t∈T.U is the vehicle fleet size.The revenues and costs associated with operating the system are as follows:at is the revenue for one unit of met demands in period t.bt is the penalty cost for one unit of unmet demand in period t.c is the fixed costs for one vehicle.In addition, the demand for vehicles is given by the following:Qitmin is the minimum demand for working service at location i in period t. The minimum demand must be satisfied by vehicles dispatched from other terminals.Qitmax is the maximum demand for working service at location i in period t. The maximum demand may not be met. But the penalty cost for unmet demand will generate.Finally, the parameters are needed to describe the system:ξ is these demands which can be serviced by one vehicle.djk is the distance between any pair of terminals j and k.D is the maximum coverage distance for any vehicle at any terminal.αjk is 0-1 parameter. αjk=1 if the distance djk≤D, or αjk=0 otherwise.We assume that all parameters are deterministic and known.


### 3.3. Model Formulation

Given the above notations for the parameters and decision variables, we present the formulation as follows:(1)MIPmaxFx=ξ∑t∈T∑i∈G∑j∈Gatxijt-∑t∈T∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U(2)subject  to:∑i∈G∑j∈Gxijt≤U,∀t∈T(3)ξ∑i∈Gxijt≥Qj,t+1min,∀j∈G,∀t∈T(4)ξ∑i∈Gxijt≤∑k∈GαjkQk,t+1max,∀j∈G,∀t∈T(5)αjk=1,djk≤D,∀j,k∈G0,djk>D,∀j,k∈G(6)∑i∈Gxijt=∑i∈Gxjit+1,∀t∈T(7)U,xjit≥0,and  integer∀i,j∈G,∀t∈T.The objective function (1) includes terms for revenues, penalty costs for unmet demand, and ownership cost for vehicles. It intends to maximize the total revenue of the system throughout the planning horizon. Constraint (2) restricts that the total number of working vehicle used cannot exceed the fleet size. Constraints (3) ensure that the minimum demand must be met. Constraints (4) impose an upper limit for the service capacity of the working vehicle at each location in each time period. Constraints (5) are coverage restriction and indicate the coverage relations between the demand nodes j and candidate locations k, that is, αjk=1 if djk⩽D, or αjk=0 otherwise. Constraints (6) are conservation of flow constraints for vehicles at each location in each time period. Constraints (7) ensure that U and xjit are always nonnegative and integer. The nominal model of DWVS-DD can be solved as a mixed integer program (MIP) by CPLEX solver.


## 3.1. Problem Description

LetG represent working service network. V is the set of working service station set in the network G. We assume that time is divided into a set of discrete time periods T={t∣t=1,…,M} where M is the length of the planning horizon. We also assume that there exist demands for vehicle work service at terminal i, i∈V, in period t, t∈T. When vehicles serve demands, the revenues will generate. We assume a unit revenue per served demand in period t, denoted as at. Serving demand results in the relocation of vehicles between various locations. It implies the need for redistribution of vehicles over the working service network from locations at which they have become idle to locations at which they can be reused. The minimum demands and maximum demands can be, respectively, represented as Qitmin and Qitmax at terminal i in period t. These demands induce vehicles available to serve them. The minimum demands Qitmin must be met, but maximum demands Qitmax are not. If insufficient vehicles are available at location i in period t to meet maximum demand, the penalty cost for unmet demand will generate. We denote the unit penalty cost per period for unmet demand by bt. The level of demand in units of vehicle loads is assumed to be specified as data. We consider ξ to be these demands which can be serviced by one vehicle. Let djk be the distance between any pair of terminal j and k. The demand of terminal k can be covered by vehicles located in j if only the distance djk≤D, where D is the maximum coverage distance. Considering the expense of purchasing or renting vehicle, we assume that the fixed costs of using vehicles are constant and denoted by c for using one vehicle. The main purpose of the DWVS-DD is to propose working vehicle assignment plan for serving as many demands as possible in the given planning horizon at the highest possible profit. Owning or leasing a fleet of vehicles is generally quite costly, so it is natural to try to optimize the size of the required fleet. We emphasize the tradeoff among the investment for establishing a suitable fleet (i.e., the fixed cost), the benefits for meeting demands (i.e., the revenue for serving demands), and the loss of benefits for failing to satisfy demands (i.e., the penalty cost for unmet demands). Dynamic working service network with dual demands is shown in Figure 1.Figure 1
Dynamic working service network with dual demands.


## 3.2. Problem Definition and Notation

We assume that planning horizon is divided into a set of discrete instantsT={t∣t=1,…,M} where M is the length of the planning horizon. A network is represented by graph G=(V,E) where V is the set of terminal. E is the set of link in the network. We present the complete notation for the problem here.Quickly summarizing the notation, we have the following decision variables:xijt is the number of working vehicles dispatched from terminal i to terminal j in period t, i,j∈N, t∈T.U is the vehicle fleet size.The revenues and costs associated with operating the system are as follows:at is the revenue for one unit of met demands in period t.bt is the penalty cost for one unit of unmet demand in period t.c is the fixed costs for one vehicle.In addition, the demand for vehicles is given by the following:Qitmin is the minimum demand for working service at location i in period t. The minimum demand must be satisfied by vehicles dispatched from other terminals.Qitmax is the maximum demand for working service at location i in period t. The maximum demand may not be met. But the penalty cost for unmet demand will generate.Finally, the parameters are needed to describe the system:ξ is these demands which can be serviced by one vehicle.djk is the distance between any pair of terminals j and k.D is the maximum coverage distance for any vehicle at any terminal.αjk is 0-1 parameter. αjk=1 if the distance djk≤D, or αjk=0 otherwise.We assume that all parameters are deterministic and known.


## 3.3. Model Formulation

Given the above notations for the parameters and decision variables, we present the formulation as follows:(1)MIPmaxFx=ξ∑t∈T∑i∈G∑j∈Gatxijt-∑t∈T∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U(2)subject  to:∑i∈G∑j∈Gxijt≤U,∀t∈T(3)ξ∑i∈Gxijt≥Qj,t+1min,∀j∈G,∀t∈T(4)ξ∑i∈Gxijt≤∑k∈GαjkQk,t+1max,∀j∈G,∀t∈T(5)αjk=1,djk≤D,∀j,k∈G0,djk>D,∀j,k∈G(6)∑i∈Gxijt=∑i∈Gxjit+1,∀t∈T(7)U,xjit≥0,and  integer∀i,j∈G,∀t∈T.The objective function (1) includes terms for revenues, penalty costs for unmet demand, and ownership cost for vehicles. It intends to maximize the total revenue of the system throughout the planning horizon. Constraint (2) restricts that the total number of working vehicle used cannot exceed the fleet size. Constraints (3) ensure that the minimum demand must be met. Constraints (4) impose an upper limit for the service capacity of the working vehicle at each location in each time period. Constraints (5) are coverage restriction and indicate the coverage relations between the demand nodes j and candidate locations k, that is, αjk=1 if djk⩽D, or αjk=0 otherwise. Constraints (6) are conservation of flow constraints for vehicles at each location in each time period. Constraints (7) ensure that U and xjit are always nonnegative and integer. The nominal model of DWVS-DD can be solved as a mixed integer program (MIP) by CPLEX solver.


## 4. Reconstruction of the Model Using Preset Control Parameters

We useE[Ft+1(x)] to denote an expected value relative to xt+1. The expectation functional E[Ft+1(x)] is called the stage t expected recourse function. Now we introduce the expected recourse function into the MIP. The objective function can be expressed in the recursive form by(8)max⁡Ftx=ξ∑i∈G∑j∈Gatxijt-∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U+EFt+1x.


### 4.1. Reconstruction of the Model with Single Preset Incremental Parameters

#### 4.1.1. Preset Total Incremental Profit Parameters

We denoteδj,t+1 as the total contribution of adding one loaded vehicle at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1 depict the marginal profit of additional vehicle, we call them as preset incremental profit parameter (PIPP).


#### 4.1.2. Reconstruction Model with Single Preset Incremental Parameters

It is common sense that the total expected profits in each terminal at each time period depend on the number of available vehicles there. Thus, the total expected profits in each terminal grow linearly with the number of available vehicles. Here, we make substitution of expected recourse function by a linear function of marginal profit and vehicle number.We can now define the state of DWVS-DD attth time period, that is, Ut∣Uj,t,j∈N. Note that the state of DWVS-DD at tth time period is given by the total vehicle supply in each terminal. By replacing the expectation recourse function E[Ft+1(x)] with preset total incremental profit parameters δj,t+1, the modified stage t+1 expected recourse function becomes(9)EFt+1x=∑j∈Gδj+1Uj,t+1.We also note that(10)Uj,t+1=∑i∈Gxijt.Substituting them intoE[Ft+1(x)] gives(11)EFt+1x=∑j∈Gδj,t+1∑i∈Gxijt.Substituting (11) into formula (8), we arrive at the local problem which is the problem to be solved at every time period. The new formulation of the local problem at single time period is represented as follows, called reconstruction model with single preset incremental parameters (RM-SPIP):(12)RM-SPIPmaxFtx=ξ∑i∈G∑j∈Gatxijt-∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U+∑j∈Gδj,t+1∑i∈Gxijt=∑i∈G∑j∈Gatξ+btξ+δj,t+1xijt-∑j∈GbtQjtmax-c·Us.t.Constraints  (2)–(7).


### 4.2. Reconstruction of the Model with Double Preset Incremental-Decremental Parameters

#### 4.2.1. Preset Incremental Revenue Parameters

Letδj,t+1+ be the revenue of adding one vehicle to servicing demand at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1+ depict the marginal revenue of additional vehicle, we call them as preset incremental revenue parameter (PIRP).


#### 4.2.2. Preset Decremental Cost Parameters

The same approach is adopted. We denoteδj,t+1- as the effect on penalty cost of adding one vehicle to servicing demand at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1- depict the marginal penalty cost of additional vehicle, we call them as preset decremental cost parameter (PDCP).


#### 4.2.3. Reconstructing Model with Double Preset Incremental-Decremental Parameters

By replacing the expectation recourse functionE[Ft+1(x)] with double preset incremental-decremental parameters δj,t+1+ and δj,t+1-, the modified stage t+1 expected recourse function becomes(13)EFt+1x=∑j∈Gδj,t+1+Uj,t+1+∑j∈Gδj,t+1-Uj,t+1.AndUj,t+1=∑i∈Gxijt, E[Ft+1(x)] can be written as(14)EFt+1x=∑j∈Gδj,t+1+∑i∈Gxijt+∑j∈Gδj,t+1-∑i∈Gxijt.Substituting (14) into formula (8), we arrive at the local problem for each time period. The model can be reformulated in piecewise form as follows. We name this new form as reconstruction model with double preset incremental-decremental parameters (RM-DPIDP).(15)RM-DPIDPmaxFtx=ξ∑i∈G∑j∈Gatxijt-∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U+∑j∈Gδj,t+1+∑i∈Gxijt+∑j∈Gδj,t+1-∑i∈Gxijt=∑i∈G∑j∈Gatξ+δj,t+1+xijt-∑j∈GbtQjtmax+∑i∈G∑j∈Gbtξ+δj,t+1-xijt-c·Us.t.Constraints  (2)–(7).


## 4.1. Reconstruction of the Model with Single Preset Incremental Parameters

### 4.1.1. Preset Total Incremental Profit Parameters

We denoteδj,t+1 as the total contribution of adding one loaded vehicle at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1 depict the marginal profit of additional vehicle, we call them as preset incremental profit parameter (PIPP).


### 4.1.2. Reconstruction Model with Single Preset Incremental Parameters

It is common sense that the total expected profits in each terminal at each time period depend on the number of available vehicles there. Thus, the total expected profits in each terminal grow linearly with the number of available vehicles. Here, we make substitution of expected recourse function by a linear function of marginal profit and vehicle number.We can now define the state of DWVS-DD attth time period, that is, Ut∣Uj,t,j∈N. Note that the state of DWVS-DD at tth time period is given by the total vehicle supply in each terminal. By replacing the expectation recourse function E[Ft+1(x)] with preset total incremental profit parameters δj,t+1, the modified stage t+1 expected recourse function becomes(9)EFt+1x=∑j∈Gδj+1Uj,t+1.We also note that(10)Uj,t+1=∑i∈Gxijt.Substituting them intoE[Ft+1(x)] gives(11)EFt+1x=∑j∈Gδj,t+1∑i∈Gxijt.Substituting (11) into formula (8), we arrive at the local problem which is the problem to be solved at every time period. The new formulation of the local problem at single time period is represented as follows, called reconstruction model with single preset incremental parameters (RM-SPIP):(12)RM-SPIPmaxFtx=ξ∑i∈G∑j∈Gatxijt-∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U+∑j∈Gδj,t+1∑i∈Gxijt=∑i∈G∑j∈Gatξ+btξ+δj,t+1xijt-∑j∈GbtQjtmax-c·Us.t.Constraints  (2)–(7).


## 4.1.1. Preset Total Incremental Profit Parameters

We denoteδj,t+1 as the total contribution of adding one loaded vehicle at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1 depict the marginal profit of additional vehicle, we call them as preset incremental profit parameter (PIPP).


## 4.1.2. Reconstruction Model with Single Preset Incremental Parameters

It is common sense that the total expected profits in each terminal at each time period depend on the number of available vehicles there. Thus, the total expected profits in each terminal grow linearly with the number of available vehicles. Here, we make substitution of expected recourse function by a linear function of marginal profit and vehicle number.We can now define the state of DWVS-DD attth time period, that is, Ut∣Uj,t,j∈N. Note that the state of DWVS-DD at tth time period is given by the total vehicle supply in each terminal. By replacing the expectation recourse function E[Ft+1(x)] with preset total incremental profit parameters δj,t+1, the modified stage t+1 expected recourse function becomes(9)EFt+1x=∑j∈Gδj+1Uj,t+1.We also note that(10)Uj,t+1=∑i∈Gxijt.Substituting them intoE[Ft+1(x)] gives(11)EFt+1x=∑j∈Gδj,t+1∑i∈Gxijt.Substituting (11) into formula (8), we arrive at the local problem which is the problem to be solved at every time period. The new formulation of the local problem at single time period is represented as follows, called reconstruction model with single preset incremental parameters (RM-SPIP):(12)RM-SPIPmaxFtx=ξ∑i∈G∑j∈Gatxijt-∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U+∑j∈Gδj,t+1∑i∈Gxijt=∑i∈G∑j∈Gatξ+btξ+δj,t+1xijt-∑j∈GbtQjtmax-c·Us.t.Constraints  (2)–(7).


## 4.2. Reconstruction of the Model with Double Preset Incremental-Decremental Parameters

### 4.2.1. Preset Incremental Revenue Parameters

Letδj,t+1+ be the revenue of adding one vehicle to servicing demand at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1+ depict the marginal revenue of additional vehicle, we call them as preset incremental revenue parameter (PIRP).


### 4.2.2. Preset Decremental Cost Parameters

The same approach is adopted. We denoteδj,t+1- as the effect on penalty cost of adding one vehicle to servicing demand at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1- depict the marginal penalty cost of additional vehicle, we call them as preset decremental cost parameter (PDCP).


### 4.2.3. Reconstructing Model with Double Preset Incremental-Decremental Parameters

By replacing the expectation recourse functionE[Ft+1(x)] with double preset incremental-decremental parameters δj,t+1+ and δj,t+1-, the modified stage t+1 expected recourse function becomes(13)EFt+1x=∑j∈Gδj,t+1+Uj,t+1+∑j∈Gδj,t+1-Uj,t+1.AndUj,t+1=∑i∈Gxijt, E[Ft+1(x)] can be written as(14)EFt+1x=∑j∈Gδj,t+1+∑i∈Gxijt+∑j∈Gδj,t+1-∑i∈Gxijt.Substituting (14) into formula (8), we arrive at the local problem for each time period. The model can be reformulated in piecewise form as follows. We name this new form as reconstruction model with double preset incremental-decremental parameters (RM-DPIDP).(15)RM-DPIDPmaxFtx=ξ∑i∈G∑j∈Gatxijt-∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U+∑j∈Gδj,t+1+∑i∈Gxijt+∑j∈Gδj,t+1-∑i∈Gxijt=∑i∈G∑j∈Gatξ+δj,t+1+xijt-∑j∈GbtQjtmax+∑i∈G∑j∈Gbtξ+δj,t+1-xijt-c·Us.t.Constraints  (2)–(7).


## 4.2.1. Preset Incremental Revenue Parameters

Letδj,t+1+ be the revenue of adding one vehicle to servicing demand at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1+ depict the marginal revenue of additional vehicle, we call them as preset incremental revenue parameter (PIRP).


## 4.2.2. Preset Decremental Cost Parameters

The same approach is adopted. We denoteδj,t+1- as the effect on penalty cost of adding one vehicle to servicing demand at terminal j starting at t+1 time period, through the rest planning horizon. Because δj,t+1- depict the marginal penalty cost of additional vehicle, we call them as preset decremental cost parameter (PDCP).


## 4.2.3. Reconstructing Model with Double Preset Incremental-Decremental Parameters

By replacing the expectation recourse functionE[Ft+1(x)] with double preset incremental-decremental parameters δj,t+1+ and δj,t+1-, the modified stage t+1 expected recourse function becomes(13)EFt+1x=∑j∈Gδj,t+1+Uj,t+1+∑j∈Gδj,t+1-Uj,t+1.AndUj,t+1=∑i∈Gxijt, E[Ft+1(x)] can be written as(14)EFt+1x=∑j∈Gδj,t+1+∑i∈Gxijt+∑j∈Gδj,t+1-∑i∈Gxijt.Substituting (14) into formula (8), we arrive at the local problem for each time period. The model can be reformulated in piecewise form as follows. We name this new form as reconstruction model with double preset incremental-decremental parameters (RM-DPIDP).(15)RM-DPIDPmaxFtx=ξ∑i∈G∑j∈Gatxijt-∑j∈GbtQjtmax-ξ∑i∈Gxijt-c·U+∑j∈Gδj,t+1+∑i∈Gxijt+∑j∈Gδj,t+1-∑i∈Gxijt=∑i∈G∑j∈Gatξ+δj,t+1+xijt-∑j∈GbtQjtmax+∑i∈G∑j∈Gbtξ+δj,t+1-xijt-c·Us.t.Constraints  (2)–(7).


## 5. Approach for Preset Control Parameter

The preset control parameter results in decoupling the problems for different time period. In section, we will develop an interactive procedure to provide approximations of the preset control parameters.


### 5.1. Procedure of the Sampling Data

#### 5.1.1. Determining Initial Vehicle Distribution

Step 1.1. Since all minimum demand and maximum demand are available for the first time, we have Qi,1min and Qi,1max.Step 1.2. Add a virtual source terminal S into working service network G(V,E). In Figure 2, there are only the outbound arcs for source terminal S.Figure 2
Dynamic working network for virtual time period.The formulation of local problem for virtual time period is denoted as LP-VTP. This model includes the following objective function and constraints:(16)LP-VTPmaxFx=ξ∑i∈Gxsi0-c·Usubject  to:∑i∈Gxsi0=Uξ·xsi0≥Qi,1min,∀i∈Gξ·xsi0≤∑k∈Gαik·Qk,1max,∀i∈Gαik=1,dik≤D,∀i,k∈G0,dik>D,∀i,k∈GU,xsi0≥0,and  integer∀i∈G.Because we pose this local problem in the format of an integer linear program, CPLEX solver can be used. Optimal solutionsxsi0 can be obtained by using CPLEX for solving LP-VTP.Step 1.3. Initial vehicle distribution is obtained according to Ui,1=xsi0.


#### 5.1.2. Sampling Data with Solving Local Problem

By solving local problem at each time period, the data can be obtained. The procedure of sampling data procedure is explained as follows.Step 2.1. The state vector, that is, {Ut∣Uit,i∈G}, is updated by equation Uit=∑j∈Gxji,(t-1).Step 2.2. Since minimum demand and maximum demand are deterministic and known for the whole planning horizon, we have Qj,t+1min and Qj,t+1max.Step 2.3. Solve local problem (LP), one for each time period, by CPLEX solver to obtain optimal solution xijt. The formulation of the LP is shown as follows:(17)LPmaxFt=ξ∑i∈GatUit-∑i∈GbtQitmax-ξUit-c∑i∈GUitsubject  to:∑j∈Gxijt≤Uit,∀i∈Gξ∑i∈Gxijt≥Qj,t+1min,∀j∈Gξ∑i∈Gxijt≤∑k∈GαjkQk,t+1max,∀j∈Gαjk=1,djk≤D,∀j,k∈G0,djk>D,∀j,k∈Gxijt≥0,and  integer∀i,j∈G.Step 2.4. Taking optimal solution xijt into the objective function of local problem, {Fit,Fit+,Fit-} can be obtained, where {Fit,Fit+,Fit-} denotes, respectively, total profit, revenue, and penalty cost for each time period.Step 2.5. Record these data, that is, {Uit,Qitmin,Qitmax,Fit,Fit+,Fit-}.


### 5.2. Modeling for Coupled Correlation

#### 5.2.1. Coupled Correlation Function with Single Preset Control Parameters (CCF-SPCP)

The total profit function is a function of vehicle supply, minimum demand, and maximum demand. We generate a quadratic polynomial function for the effect of vehicle supply, minimum demand, and maximum demand on the total profits in each terminal where the function is used to approximate the incremental profit parameter of RM-SPIP. The quadratic polynomial function for approximating the single preset incremental parameter of RM-SPIP has the following form:(18)CCF-SPCPFiUi,Qimin,Qimax=αi1Ui2+αi2Qimin2+αi3Qimax2+αi4UiQimin+αi5UiQimax+αi6QiminQimax+αi7Ui+αi8Qimin+αi9Qimax+αi10,∀i∈G.Above coupled correlation function with single preset control parameters is denoted as CCF-SPCP.


#### 5.2.2. Coupled Correlation Function with Double Preset Control Parameters (CCF-DPCP)

The coupled correlation is set up in a control theoretic setting. The pair{Fit+,Fit-} represents the system outputs. The set {Uit,Qitmin,Qitmax} represents the system inputs. Multi-input and multi-output control systems are set up. We generate a quadratic polynomial equation for the effect of vehicle supply, minimum demand, and maximum demand on the revenue and penalty cost in each terminal where the function is used to approximate the incremental revenue parameter and decremental cost parameters of RM-DPIDP. The quadratic polynomial function for approximating the double preset incremental-decremental parameters of RM-DPIDP has the form as follows:(19)CCF-DPCPFi+Ui,Qimin,Qimax=βi1Ui2+βi2Qimin2+βi3Qimax2+βi4UiQimin+βi5UiQimax+βi6QiminQimax+βi7Ui+βi8Qimin+βi9Qimax+βi10,∀i∈GFi-Ui,Qimin,Qimax=γi1Ui2+γi2Qimin2+γi3Qimax2+γi4UiQimin+γi5UiQimax+γi6QiminQimax+γi7Ui+γi8Qimin+γi9Qimax+γi10,i∈G.Above coupled correlation function with double preset control parameters is denoted as CCF-DPCP.


### 5.3. Fitting Parameters of Coupled Correlation Function

#### 5.3.1. Sampling Data Sets for Fitting Parameters

By solving local problem at each time period, the data sets can be obtained. Solution of local problem, that is,xijt, is obtained by CPLEX solver. {Fit,Fit+,Fit-} is carried on by taking xijt into the objective function of local problem. State vector {Uit} is obtained by updated approach of local problem. In order to fit parameters of coupled correlation function, these data are split into three data sets, that is, {Fit,Uit,Qitmin,Qitmax∣i∈G,t∈T}, Fit+,Uit,Qitmin,Qitmax∣i∈G,t∈T, and Fit-,Uit,Qitmin,Qitmax∣i∈G,t∈T.


#### 5.3.2. Fitting the Parameters of Coupled Correlation Function

We use the data setFit,Uit,Qitmin,Qitmax∣i∈G,t∈T to fit the parameter of RM-SPIP with regression method. Thus these parameters αim∣i∈G,m=1,…,10 are derived. The coupled correlation function CCF-SPCP is obtained.Again, using the same approach, we introduce the data setsFit+,Uit,Qitmin,Qitmax∣i∈G,t∈T and Fit-,Uit,Qitmin,Qitmax∣i∈G,t∈T into the RM-DPIDP for fitting these parameters βim∣i∈G,m=1,…,10 and βim∣i∈G,m=1,…,10. The coupled correlation function CCF-DPCP is obtained.


### 5.4. Computing the Preset Control Parameters of Coupled Correlation Function

#### 5.4.1. Computing Single Preset Control Parameter with CCF-SPCP

The coupled correlation function CCF-SPCP implies the effect of vehicle supplyUj, minimum demand Qjmin, and maximum demand Qjmax on the profits Fj. As the derivative of Fj(Uj,Qjmin,Qjmax) with respect to Uj shows the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1 is given by(20)δj,t+1=∂FjUj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset incremental profit parameter (PIPP) is shown in following formula:(21)δj,t+1=∂FjUj,Qjmin,Qjmax∂U-jUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2αj1Uj+αj4Qjmin+αj5Qjmax+αj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2αj1Uj,t+1+αj4Qj,t+1min+αj5Qj,t+1max+αj7.


#### 5.4.2. Computing Double Preset Control Parameter with CCF-DPCP

We use the same approach to compute the double preset control parameter of coupled correlation function CCF-DPCP. The coupled correlation function implies the effect of vehicle supplyUj, minimum demand Qjmin and maximum demand Qjmax on revenue Fj+ and penalty cost Fj-. As the derivative of Fj+(Uj,Qjmin,Qjmax) with respect to Uj shows the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1+ is given by(22)δj,t+1+=∂Fj+Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset incremental revenue parameter (PIRP) is shown in the following formula:(23)δj,t+1+=∂Fj+Uj,Qjmin,Qjmax∂U-jUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2βj1Uj+βj4Qjmin+βj5Qjmax+βj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2βj1Uj,t+1+βj4Qj,t+1min+βj5Qj,t+1max+βj7.Correspondingly, as the derivative ofFj-(Uj,Qjmin,Qjmax) with respect to Uj nicely depicts the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1- is written as(24)δj,t+1-=∂Fj-Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset decremental cost parameter (PDCP) is shown in the following formula:(25)δj,t+1-=∂Fj-Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2γj1Uj+γj4Qjmin+γj5Qjmax+γj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2γj1Uj,t+1+γj4Qj,t+1min+γj5Qj,t+1max+γj7.


## 5.1. Procedure of the Sampling Data

### 5.1.1. Determining Initial Vehicle Distribution

Step 1.1. Since all minimum demand and maximum demand are available for the first time, we have Qi,1min and Qi,1max.Step 1.2. Add a virtual source terminal S into working service network G(V,E). In Figure 2, there are only the outbound arcs for source terminal S.Figure 2
Dynamic working network for virtual time period.The formulation of local problem for virtual time period is denoted as LP-VTP. This model includes the following objective function and constraints:(16)LP-VTPmaxFx=ξ∑i∈Gxsi0-c·Usubject  to:∑i∈Gxsi0=Uξ·xsi0≥Qi,1min,∀i∈Gξ·xsi0≤∑k∈Gαik·Qk,1max,∀i∈Gαik=1,dik≤D,∀i,k∈G0,dik>D,∀i,k∈GU,xsi0≥0,and  integer∀i∈G.Because we pose this local problem in the format of an integer linear program, CPLEX solver can be used. Optimal solutionsxsi0 can be obtained by using CPLEX for solving LP-VTP.Step 1.3. Initial vehicle distribution is obtained according to Ui,1=xsi0.


### 5.1.2. Sampling Data with Solving Local Problem

By solving local problem at each time period, the data can be obtained. The procedure of sampling data procedure is explained as follows.Step 2.1. The state vector, that is, {Ut∣Uit,i∈G}, is updated by equation Uit=∑j∈Gxji,(t-1).Step 2.2. Since minimum demand and maximum demand are deterministic and known for the whole planning horizon, we have Qj,t+1min and Qj,t+1max.Step 2.3. Solve local problem (LP), one for each time period, by CPLEX solver to obtain optimal solution xijt. The formulation of the LP is shown as follows:(17)LPmaxFt=ξ∑i∈GatUit-∑i∈GbtQitmax-ξUit-c∑i∈GUitsubject  to:∑j∈Gxijt≤Uit,∀i∈Gξ∑i∈Gxijt≥Qj,t+1min,∀j∈Gξ∑i∈Gxijt≤∑k∈GαjkQk,t+1max,∀j∈Gαjk=1,djk≤D,∀j,k∈G0,djk>D,∀j,k∈Gxijt≥0,and  integer∀i,j∈G.Step 2.4. Taking optimal solution xijt into the objective function of local problem, {Fit,Fit+,Fit-} can be obtained, where {Fit,Fit+,Fit-} denotes, respectively, total profit, revenue, and penalty cost for each time period.Step 2.5. Record these data, that is, {Uit,Qitmin,Qitmax,Fit,Fit+,Fit-}.


## 5.1.1. Determining Initial Vehicle Distribution

Step 1.1. Since all minimum demand and maximum demand are available for the first time, we have Qi,1min and Qi,1max.Step 1.2. Add a virtual source terminal S into working service network G(V,E). In Figure 2, there are only the outbound arcs for source terminal S.Figure 2
Dynamic working network for virtual time period.The formulation of local problem for virtual time period is denoted as LP-VTP. This model includes the following objective function and constraints:(16)LP-VTPmaxFx=ξ∑i∈Gxsi0-c·Usubject  to:∑i∈Gxsi0=Uξ·xsi0≥Qi,1min,∀i∈Gξ·xsi0≤∑k∈Gαik·Qk,1max,∀i∈Gαik=1,dik≤D,∀i,k∈G0,dik>D,∀i,k∈GU,xsi0≥0,and  integer∀i∈G.Because we pose this local problem in the format of an integer linear program, CPLEX solver can be used. Optimal solutionsxsi0 can be obtained by using CPLEX for solving LP-VTP.Step 1.3. Initial vehicle distribution is obtained according to Ui,1=xsi0.


## 5.1.2. Sampling Data with Solving Local Problem

By solving local problem at each time period, the data can be obtained. The procedure of sampling data procedure is explained as follows.Step 2.1. The state vector, that is, {Ut∣Uit,i∈G}, is updated by equation Uit=∑j∈Gxji,(t-1).Step 2.2. Since minimum demand and maximum demand are deterministic and known for the whole planning horizon, we have Qj,t+1min and Qj,t+1max.Step 2.3. Solve local problem (LP), one for each time period, by CPLEX solver to obtain optimal solution xijt. The formulation of the LP is shown as follows:(17)LPmaxFt=ξ∑i∈GatUit-∑i∈GbtQitmax-ξUit-c∑i∈GUitsubject  to:∑j∈Gxijt≤Uit,∀i∈Gξ∑i∈Gxijt≥Qj,t+1min,∀j∈Gξ∑i∈Gxijt≤∑k∈GαjkQk,t+1max,∀j∈Gαjk=1,djk≤D,∀j,k∈G0,djk>D,∀j,k∈Gxijt≥0,and  integer∀i,j∈G.Step 2.4. Taking optimal solution xijt into the objective function of local problem, {Fit,Fit+,Fit-} can be obtained, where {Fit,Fit+,Fit-} denotes, respectively, total profit, revenue, and penalty cost for each time period.Step 2.5. Record these data, that is, {Uit,Qitmin,Qitmax,Fit,Fit+,Fit-}.


## 5.2. Modeling for Coupled Correlation

### 5.2.1. Coupled Correlation Function with Single Preset Control Parameters (CCF-SPCP)

The total profit function is a function of vehicle supply, minimum demand, and maximum demand. We generate a quadratic polynomial function for the effect of vehicle supply, minimum demand, and maximum demand on the total profits in each terminal where the function is used to approximate the incremental profit parameter of RM-SPIP. The quadratic polynomial function for approximating the single preset incremental parameter of RM-SPIP has the following form:(18)CCF-SPCPFiUi,Qimin,Qimax=αi1Ui2+αi2Qimin2+αi3Qimax2+αi4UiQimin+αi5UiQimax+αi6QiminQimax+αi7Ui+αi8Qimin+αi9Qimax+αi10,∀i∈G.Above coupled correlation function with single preset control parameters is denoted as CCF-SPCP.


### 5.2.2. Coupled Correlation Function with Double Preset Control Parameters (CCF-DPCP)

The coupled correlation is set up in a control theoretic setting. The pair{Fit+,Fit-} represents the system outputs. The set {Uit,Qitmin,Qitmax} represents the system inputs. Multi-input and multi-output control systems are set up. We generate a quadratic polynomial equation for the effect of vehicle supply, minimum demand, and maximum demand on the revenue and penalty cost in each terminal where the function is used to approximate the incremental revenue parameter and decremental cost parameters of RM-DPIDP. The quadratic polynomial function for approximating the double preset incremental-decremental parameters of RM-DPIDP has the form as follows:(19)CCF-DPCPFi+Ui,Qimin,Qimax=βi1Ui2+βi2Qimin2+βi3Qimax2+βi4UiQimin+βi5UiQimax+βi6QiminQimax+βi7Ui+βi8Qimin+βi9Qimax+βi10,∀i∈GFi-Ui,Qimin,Qimax=γi1Ui2+γi2Qimin2+γi3Qimax2+γi4UiQimin+γi5UiQimax+γi6QiminQimax+γi7Ui+γi8Qimin+γi9Qimax+γi10,i∈G.Above coupled correlation function with double preset control parameters is denoted as CCF-DPCP.


## 5.2.1. Coupled Correlation Function with Single Preset Control Parameters (CCF-SPCP)

The total profit function is a function of vehicle supply, minimum demand, and maximum demand. We generate a quadratic polynomial function for the effect of vehicle supply, minimum demand, and maximum demand on the total profits in each terminal where the function is used to approximate the incremental profit parameter of RM-SPIP. The quadratic polynomial function for approximating the single preset incremental parameter of RM-SPIP has the following form:(18)CCF-SPCPFiUi,Qimin,Qimax=αi1Ui2+αi2Qimin2+αi3Qimax2+αi4UiQimin+αi5UiQimax+αi6QiminQimax+αi7Ui+αi8Qimin+αi9Qimax+αi10,∀i∈G.Above coupled correlation function with single preset control parameters is denoted as CCF-SPCP.


## 5.2.2. Coupled Correlation Function with Double Preset Control Parameters (CCF-DPCP)

The coupled correlation is set up in a control theoretic setting. The pair{Fit+,Fit-} represents the system outputs. The set {Uit,Qitmin,Qitmax} represents the system inputs. Multi-input and multi-output control systems are set up. We generate a quadratic polynomial equation for the effect of vehicle supply, minimum demand, and maximum demand on the revenue and penalty cost in each terminal where the function is used to approximate the incremental revenue parameter and decremental cost parameters of RM-DPIDP. The quadratic polynomial function for approximating the double preset incremental-decremental parameters of RM-DPIDP has the form as follows:(19)CCF-DPCPFi+Ui,Qimin,Qimax=βi1Ui2+βi2Qimin2+βi3Qimax2+βi4UiQimin+βi5UiQimax+βi6QiminQimax+βi7Ui+βi8Qimin+βi9Qimax+βi10,∀i∈GFi-Ui,Qimin,Qimax=γi1Ui2+γi2Qimin2+γi3Qimax2+γi4UiQimin+γi5UiQimax+γi6QiminQimax+γi7Ui+γi8Qimin+γi9Qimax+γi10,i∈G.Above coupled correlation function with double preset control parameters is denoted as CCF-DPCP.


## 5.3. Fitting Parameters of Coupled Correlation Function

### 5.3.1. Sampling Data Sets for Fitting Parameters

By solving local problem at each time period, the data sets can be obtained. Solution of local problem, that is,xijt, is obtained by CPLEX solver. {Fit,Fit+,Fit-} is carried on by taking xijt into the objective function of local problem. State vector {Uit} is obtained by updated approach of local problem. In order to fit parameters of coupled correlation function, these data are split into three data sets, that is, {Fit,Uit,Qitmin,Qitmax∣i∈G,t∈T}, Fit+,Uit,Qitmin,Qitmax∣i∈G,t∈T, and Fit-,Uit,Qitmin,Qitmax∣i∈G,t∈T.


### 5.3.2. Fitting the Parameters of Coupled Correlation Function

We use the data setFit,Uit,Qitmin,Qitmax∣i∈G,t∈T to fit the parameter of RM-SPIP with regression method. Thus these parameters αim∣i∈G,m=1,…,10 are derived. The coupled correlation function CCF-SPCP is obtained.Again, using the same approach, we introduce the data setsFit+,Uit,Qitmin,Qitmax∣i∈G,t∈T and Fit-,Uit,Qitmin,Qitmax∣i∈G,t∈T into the RM-DPIDP for fitting these parameters βim∣i∈G,m=1,…,10 and βim∣i∈G,m=1,…,10. The coupled correlation function CCF-DPCP is obtained.


## 5.3.1. Sampling Data Sets for Fitting Parameters

By solving local problem at each time period, the data sets can be obtained. Solution of local problem, that is,xijt, is obtained by CPLEX solver. {Fit,Fit+,Fit-} is carried on by taking xijt into the objective function of local problem. State vector {Uit} is obtained by updated approach of local problem. In order to fit parameters of coupled correlation function, these data are split into three data sets, that is, {Fit,Uit,Qitmin,Qitmax∣i∈G,t∈T}, Fit+,Uit,Qitmin,Qitmax∣i∈G,t∈T, and Fit-,Uit,Qitmin,Qitmax∣i∈G,t∈T.


## 5.3.2. Fitting the Parameters of Coupled Correlation Function

We use the data setFit,Uit,Qitmin,Qitmax∣i∈G,t∈T to fit the parameter of RM-SPIP with regression method. Thus these parameters αim∣i∈G,m=1,…,10 are derived. The coupled correlation function CCF-SPCP is obtained.Again, using the same approach, we introduce the data setsFit+,Uit,Qitmin,Qitmax∣i∈G,t∈T and Fit-,Uit,Qitmin,Qitmax∣i∈G,t∈T into the RM-DPIDP for fitting these parameters βim∣i∈G,m=1,…,10 and βim∣i∈G,m=1,…,10. The coupled correlation function CCF-DPCP is obtained.


## 5.4. Computing the Preset Control Parameters of Coupled Correlation Function

### 5.4.1. Computing Single Preset Control Parameter with CCF-SPCP

The coupled correlation function CCF-SPCP implies the effect of vehicle supplyUj, minimum demand Qjmin, and maximum demand Qjmax on the profits Fj. As the derivative of Fj(Uj,Qjmin,Qjmax) with respect to Uj shows the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1 is given by(20)δj,t+1=∂FjUj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset incremental profit parameter (PIPP) is shown in following formula:(21)δj,t+1=∂FjUj,Qjmin,Qjmax∂U-jUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2αj1Uj+αj4Qjmin+αj5Qjmax+αj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2αj1Uj,t+1+αj4Qj,t+1min+αj5Qj,t+1max+αj7.


### 5.4.2. Computing Double Preset Control Parameter with CCF-DPCP

We use the same approach to compute the double preset control parameter of coupled correlation function CCF-DPCP. The coupled correlation function implies the effect of vehicle supplyUj, minimum demand Qjmin and maximum demand Qjmax on revenue Fj+ and penalty cost Fj-. As the derivative of Fj+(Uj,Qjmin,Qjmax) with respect to Uj shows the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1+ is given by(22)δj,t+1+=∂Fj+Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset incremental revenue parameter (PIRP) is shown in the following formula:(23)δj,t+1+=∂Fj+Uj,Qjmin,Qjmax∂U-jUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2βj1Uj+βj4Qjmin+βj5Qjmax+βj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2βj1Uj,t+1+βj4Qj,t+1min+βj5Qj,t+1max+βj7.Correspondingly, as the derivative ofFj-(Uj,Qjmin,Qjmax) with respect to Uj nicely depicts the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1- is written as(24)δj,t+1-=∂Fj-Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset decremental cost parameter (PDCP) is shown in the following formula:(25)δj,t+1-=∂Fj-Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2γj1Uj+γj4Qjmin+γj5Qjmax+γj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2γj1Uj,t+1+γj4Qj,t+1min+γj5Qj,t+1max+γj7.


## 5.4.1. Computing Single Preset Control Parameter with CCF-SPCP

The coupled correlation function CCF-SPCP implies the effect of vehicle supplyUj, minimum demand Qjmin, and maximum demand Qjmax on the profits Fj. As the derivative of Fj(Uj,Qjmin,Qjmax) with respect to Uj shows the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1 is given by(20)δj,t+1=∂FjUj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset incremental profit parameter (PIPP) is shown in following formula:(21)δj,t+1=∂FjUj,Qjmin,Qjmax∂U-jUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2αj1Uj+αj4Qjmin+αj5Qjmax+αj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2αj1Uj,t+1+αj4Qj,t+1min+αj5Qj,t+1max+αj7.


## 5.4.2. Computing Double Preset Control Parameter with CCF-DPCP

We use the same approach to compute the double preset control parameter of coupled correlation function CCF-DPCP. The coupled correlation function implies the effect of vehicle supplyUj, minimum demand Qjmin and maximum demand Qjmax on revenue Fj+ and penalty cost Fj-. As the derivative of Fj+(Uj,Qjmin,Qjmax) with respect to Uj shows the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1+ is given by(22)δj,t+1+=∂Fj+Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset incremental revenue parameter (PIRP) is shown in the following formula:(23)δj,t+1+=∂Fj+Uj,Qjmin,Qjmax∂U-jUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2βj1Uj+βj4Qjmin+βj5Qjmax+βj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2βj1Uj,t+1+βj4Qj,t+1min+βj5Qj,t+1max+βj7.Correspondingly, as the derivative ofFj-(Uj,Qjmin,Qjmax) with respect to Uj nicely depicts the effect of adding one vehicle in j terminal at t+1 time period through the rest the planning horizon, δj,t+1- is written as(24)δj,t+1-=∂Fj-Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max.Accordingly, the solution approach of preset decremental cost parameter (PDCP) is shown in the following formula:(25)δj,t+1-=∂Fj-Uj,Qjmin,Qjmax∂UjUj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2γj1Uj+γj4Qjmin+γj5Qjmax+γj7Uj=Uj,t+1Qjmin=Qj,t+1min,Qjmax=Qj,t+1max=2γj1Uj,t+1+γj4Qj,t+1min+γj5Qj,t+1max+γj7.


## 6. Piecewise Method by Updating Preset Control Parameters

In this section, we develop a solution approach based on updating preset control parameters. An overview of the framework of piecewise method by updating preset control parameters (PM-PCP) is explained as follows.Stage 1 (sampling data sets).
Step 1.1. Add a virtual source terminal into working service network. The formulation of local problem for virtual time period is written. Optimal solutions xsi0 can be obtained by using CPLEX for solving local problem. Then initial vehicle distribution {Ui,1∣i∈G} is obtained.
Step 1.2. By solving local problem (LP) at each time period with CPLEX solver, optimal solutions xijt can be obtained. Taking optimal solution xijt into the objective function of local problem, {Fit,Fit+,Fit-} can be obtained. State vector {Uit} is obtained by updated approach of local problem.
Step 1.3. Record these data sets {Uit,Qitmin,Qitmax,Fit,Fit+,Fit-} in each terminal at each time period.
Step 1.4. As such, repeat Steps 1.1 to 1.3 for the whole planning horizon. In order to fit parameters of coupled correlation function, these data are split into three data sets, that is, {Fit,Uit,Qitmin,Qitmax∣i∈G,t∈T}, {Fit+,Uit,Qitmin,Qitmax∣i∈G,t∈T}, and {Fit-,Uit,Qitmin,Qitmax∣i∈Gt∈T}.Stage 2 (coupled correlation formulation).
Step 2.1. Using the data set {Fit,Uit,Qitmin,Qitmax∣i∈G,t∈T} to fit these parameters of CCF-SPCP by regression method, the coupled correlation function CCF-SPCP is formed.
Step 2.2. Using the data sets Fit+,Uit,Qitmin,Qitmax∣i∈G,t∈T and Fit+,Uit,Qitmin,Qitmax∣i∈G,t∈T to fit these parameters of CCF-DPCP by regression method, the coupled correlation function CCF-DPCP is formed.Stage 3 (piecewise method guided by preset control parameters).
Step 3.1. Single preset control parameters of RM-SPIP δj,t+1 are computed by formula (21).
Step 3.2. Taking incremental profit parameters δj,t+1 into the objective function of MIP, the piecewise form of the model (RM-SPIP) is given. The new solution xijtnew is obtained by resolving RM-SPIP using CPLEX solver for the beginning of the 1st period until the end of an appropriate planning horizon M. Further, Uitnew are obtained.
Step 3.3. Double preset control parameters of RM-DPIDP δj,t+1+ and δj,t+1- are computed by formulas (23) and (25).
Step 3.4. Taking preset incremental revenue parameter δj,t+1+ and preset decremental cost parameter δj,t+1- into the objective function of MIP, the piecewise form of the model (RM-DPIDP) is given. The new solution xijtnew is obtained by resolving RM-DPIDP using CPLEX solver for the beginning of the 1st period until the end of an appropriate planning horizon M. Further, Uitnew are obtained.


## 7. Numerical Study

In this section, we try to evaluate the quality of the PM-PCP method in terms of traditional measure such as objective function and execution time. Section7.1 describes the experimental design, and Sections 7.2–7.5 report the numerical results.


### 7.1. Instances and Test Settings

This section describes the data used in the numerical testing of the models. For each vehicle, the region and the time of first availability have to be known. In this data set, the working service network is composed of 10 terminals and of fixed-length links joining them. The length of the planning horizon is 50-time period. The length of each time period is constant 60-time unit.All vehicles are assumed to be of the same type and all demands can be met from that type of vehicle. The minimum demands at each terminal are assumed to follow Poisson distributions with mean 250. The maximum demands at each terminal are assumed to follow Poisson distributions with mean 400. The revenue for one unit of met demands is 40 dollar. The penalty cost for one unit of unmet demand is 18 dollar. The fixed cost for owning or leasing vehicle is 50,000 dollar per vehicle. The demands which can be serviced by vehicle are 100 units per vehicle. The distance between any pair of terminal are assumed to uniform distributions with mean 300. The maximum coverage distance for any vehicle at any terminal is 500 meters.In the following, the PM-PCP program for RM-SPIP and RM-DPIDP is coded by using MATLAB 2014 Edition. A Pentium IV 3.4 GHz processor with 2 GB memory is used for the computation. For solving the MIP, CPLEX solver is also used. We compare the three models using the test instances and evaluate the performance of the MIP model, RM-SPIP model, and RM-DPIDP model.


### 7.2. Performance Evaluation

In this section, the major criterion in assessing the performance of the models MIP, RM-SPIP, and RM-DPIDP is the profit generated by revenues for assigning vehicles, penalty costs for unmet demand, and ownership costs for owning vehicle in planning horizon. The PM-PCP procedure is coded by using MATLAB 2014 Edition to solve the RM-SPIP and RM-DPIDP. The MIP model is solved by CPLEX.In the experiment, we test the performance of the solution procedure on working service network. At each iteration, the objective function value for each time period is recorded. When the models MIP, RM-SPIP, and RM-DPIDP are compared, the difference in total profit is very clear. The RM-SPIP and RM-DPIDP model can generate higher the total profit than MIP model. Furthermore, we observe that the solution obtained from RM-DPIDP outperforms the solution approaches from RM-SPIP. The results obtained by RM-DPDIP, RM-SPIP, and MIP are displayed in Figure3.Figure 3
Comparison of models RM-DPDIP, RM-SPIP, and MIP.


### 7.3. Evolution of the Preset Control Parameters

The preset control parameters are important for the RM-SPIP model and RM-DPIDP model. In this section, we indicate the evolution of the preset control parameters for whole planning horizon. For the RM-SPIP model and RM-DPIDP model, the following preset control parameters are reported: preset incremental profit parameter (PIPP) for RM-SPIP model and preset incremental revenue parameter (PIRP) and preset decremental cost parameter (PDCP) for RM-DPIDP model. Figure4 shows the evolution of three types preset control parameters through 50-time period.Figure 4
Dynamic change of preset increment parameters.
(a)
Single preset parameters (preset incremental profit parameter)
(b)
Double preset parameters (preset incremental revenue parameter)
(c)
Double preset parameters (preset decremental cost parameter)


### 7.4. Numerical Results on Instances for Different Length of Planning Horizon

In this section, we use two measures of performance. The first one is the OPT, which is the value of the objective function obtained by the MIP and the optimal value obtained by RM-SPIP and RM-DPIDP. The second measure of performance is the CUP time to run CPLEX solver for MIP model and the PM-PCP program for RM-SPIP model and RM-DPIDP model.Dynamic working vehicle scheduling with dual demands service network (DWVS-DD) for different length of planning horizon is, respectively, solved by models MIP, RM-SPIP, and RM-DPIDP. For small time period size (up to 5 time period), the solving RM-SPIP and RM-DPIDP model can generally result in slightly higher total profits than that of MIP model. Nevertheless for bigger time period size (up to 50 time period), the solution of RM-SPIP and RM-DPIDP model can obviously maintain higher total profits than that of MIP. The OPT performance is shown in Figure5.Figure 5
The OPT performance of 3 models for different length of planning horizon.Additional measures are the CPU time. The required CPU time is reported to indicate the usefulness of models MIP, RM-SPIP, and RM-DPIDP. These times include the processing time needed to solve the RM-SPIP and RM-DPIDP model by PM-PCP program and solve the MIP model by CPLEX program. The computational results of the performance of the models are shown in Figure6.Figure 6
CPU time of 3 models for different length of planning horizon.


### 7.5. Numerical Results on Instances for Working Service Station Size

In this section, two measures of performance are adopted. The first one is the OPT difference, which is the difference between the value of the objective function obtained by MIP model and the optimal value obtained by RM-SPIP and RM-DPIDP model. The second measure of performance is the CUP time difference, which is the difference between the CPU time to find the optimal solution of MIP model by using CPLEX solver and the CPU time to run the PM-PCP program for RM-SPIP and RM-DPIDP model.When the models MIP, RM-SPIP, and RM-DPIDP are compared, the difference in total profit is very clear. Meanwhile, the OPT difference will increase with the working service station size. In other words, with increasing working service station size, the OPT difference will also increase. The results for the OPT difference of different working service station size are listed in Table1.Table 1
Performance for MIP, RM-SPIP, and RM- DPIDP model applied to different working service station size.
Number of service station
OPT difference ($)
CPU time (s)
MIP
RM-SPIP
RM-DPIDP
MIP
RM-SPIP
RM-DPIDP
3
232527
365392
577442
447.4
689.1
900.6
5
282930
362955
617750
462.1
689.0
910.9
8
311313
463953
635832
475.8
717.4
900.2
10
325420
507720
736300
502.8
702.1
943.4
13
399359
528024
819622
510.0
757.9
937.4
15
457170
627995
830250
937.4
777.6
985.4
18
466665
707605
978812
580.3
810.8
1015.2
20
518180
713780
1049600
602.0
805.3
1006.9
23
603231
802696
1103402
620.5
875.9
1072.4
25
668450
915075
1244350
660.6
905.4
1008.0
28
719057
1013297
1303392
678.6
903.3
1139.3
30
707980
1031880
1404500
705.1
987.7
1068.7
33
844143
1189408
1508782
766.7
1043.0
1215.7
35
846770
1264195
1710050
795.6
1052.4
1248.9
38
988489
1301029
1809572
800.8
1145.1
1251.6
40
1034820
1462020
1981000
872.1
1189.3
1338.6
43
1102095
1538160
2105762
920.8
1209.4
1397.1
45
1142130
1675355
2277350
914.5
1308.5
1437.9
48
1294961
1780801
2407352
1006.7
1336.0
1472.1
50
1308700
1904200
2599100
1042.8
1440.1
1546.8Furthermore, we have to look at the following affect in CPU time difference. Here DWVS-DD size is described by working service station size. The CUP time difference for different DWVS-DD size is described in Table1.Using polynomial curve fitting to the OPT data can provide good results. The results are shown in Figure7. Referring to the results obtained by using the PM-PCP program for RM-SPIP and RM-DPIDP model, we observe that the quality of the OPT value is improved. In comparison, the performance of PM-PCP program for RM-SPIP and RM-DPIDP is very significant when the scale of the problem becomes relatively large.Figure 7
Fitting curve of OPT for 3 models.Furthermore, using polynomial curve fitting to the CUP time data can also provide good results. The results are displayed in Figure8. In comparison, along with the increase in scale of the problem, CPU time of PM-PCP program for RM-SPIP and RM-DPIDP slightly increases.Figure 8
Fitting curve of CUP time for 3 models.


## 7.1. Instances and Test Settings

This section describes the data used in the numerical testing of the models. For each vehicle, the region and the time of first availability have to be known. In this data set, the working service network is composed of 10 terminals and of fixed-length links joining them. The length of the planning horizon is 50-time period. The length of each time period is constant 60-time unit.All vehicles are assumed to be of the same type and all demands can be met from that type of vehicle. The minimum demands at each terminal are assumed to follow Poisson distributions with mean 250. The maximum demands at each terminal are assumed to follow Poisson distributions with mean 400. The revenue for one unit of met demands is 40 dollar. The penalty cost for one unit of unmet demand is 18 dollar. The fixed cost for owning or leasing vehicle is 50,000 dollar per vehicle. The demands which can be serviced by vehicle are 100 units per vehicle. The distance between any pair of terminal are assumed to uniform distributions with mean 300. The maximum coverage distance for any vehicle at any terminal is 500 meters.In the following, the PM-PCP program for RM-SPIP and RM-DPIDP is coded by using MATLAB 2014 Edition. A Pentium IV 3.4 GHz processor with 2 GB memory is used for the computation. For solving the MIP, CPLEX solver is also used. We compare the three models using the test instances and evaluate the performance of the MIP model, RM-SPIP model, and RM-DPIDP model.


## 7.2. Performance Evaluation

In this section, the major criterion in assessing the performance of the models MIP, RM-SPIP, and RM-DPIDP is the profit generated by revenues for assigning vehicles, penalty costs for unmet demand, and ownership costs for owning vehicle in planning horizon. The PM-PCP procedure is coded by using MATLAB 2014 Edition to solve the RM-SPIP and RM-DPIDP. The MIP model is solved by CPLEX.In the experiment, we test the performance of the solution procedure on working service network. At each iteration, the objective function value for each time period is recorded. When the models MIP, RM-SPIP, and RM-DPIDP are compared, the difference in total profit is very clear. The RM-SPIP and RM-DPIDP model can generate higher the total profit than MIP model. Furthermore, we observe that the solution obtained from RM-DPIDP outperforms the solution approaches from RM-SPIP. The results obtained by RM-DPDIP, RM-SPIP, and MIP are displayed in Figure3.Figure 3
Comparison of models RM-DPDIP, RM-SPIP, and MIP.


## 7.3. Evolution of the Preset Control Parameters

The preset control parameters are important for the RM-SPIP model and RM-DPIDP model. In this section, we indicate the evolution of the preset control parameters for whole planning horizon. For the RM-SPIP model and RM-DPIDP model, the following preset control parameters are reported: preset incremental profit parameter (PIPP) for RM-SPIP model and preset incremental revenue parameter (PIRP) and preset decremental cost parameter (PDCP) for RM-DPIDP model. Figure4 shows the evolution of three types preset control parameters through 50-time period.Figure 4
Dynamic change of preset increment parameters.
(a)
Single preset parameters (preset incremental profit parameter)
(b)
Double preset parameters (preset incremental revenue parameter)
(c)
Double preset parameters (preset decremental cost parameter)


## 7.4. Numerical Results on Instances for Different Length of Planning Horizon

In this section, we use two measures of performance. The first one is the OPT, which is the value of the objective function obtained by the MIP and the optimal value obtained by RM-SPIP and RM-DPIDP. The second measure of performance is the CUP time to run CPLEX solver for MIP model and the PM-PCP program for RM-SPIP model and RM-DPIDP model.Dynamic working vehicle scheduling with dual demands service network (DWVS-DD) for different length of planning horizon is, respectively, solved by models MIP, RM-SPIP, and RM-DPIDP. For small time period size (up to 5 time period), the solving RM-SPIP and RM-DPIDP model can generally result in slightly higher total profits than that of MIP model. Nevertheless for bigger time period size (up to 50 time period), the solution of RM-SPIP and RM-DPIDP model can obviously maintain higher total profits than that of MIP. The OPT performance is shown in Figure5.Figure 5
The OPT performance of 3 models for different length of planning horizon.Additional measures are the CPU time. The required CPU time is reported to indicate the usefulness of models MIP, RM-SPIP, and RM-DPIDP. These times include the processing time needed to solve the RM-SPIP and RM-DPIDP model by PM-PCP program and solve the MIP model by CPLEX program. The computational results of the performance of the models are shown in Figure6.Figure 6
CPU time of 3 models for different length of planning horizon.


## 7.5. Numerical Results on Instances for Working Service Station Size

In this section, two measures of performance are adopted. The first one is the OPT difference, which is the difference between the value of the objective function obtained by MIP model and the optimal value obtained by RM-SPIP and RM-DPIDP model. The second measure of performance is the CUP time difference, which is the difference between the CPU time to find the optimal solution of MIP model by using CPLEX solver and the CPU time to run the PM-PCP program for RM-SPIP and RM-DPIDP model.When the models MIP, RM-SPIP, and RM-DPIDP are compared, the difference in total profit is very clear. Meanwhile, the OPT difference will increase with the working service station size. In other words, with increasing working service station size, the OPT difference will also increase. The results for the OPT difference of different working service station size are listed in Table1.Table 1
Performance for MIP, RM-SPIP, and RM- DPIDP model applied to different working service station size.
Number of service station
OPT difference ($)
CPU time (s)
MIP
RM-SPIP
RM-DPIDP
MIP
RM-SPIP
RM-DPIDP
3
232527
365392
577442
447.4
689.1
900.6
5
282930
362955
617750
462.1
689.0
910.9
8
311313
463953
635832
475.8
717.4
900.2
10
325420
507720
736300
502.8
702.1
943.4
13
399359
528024
819622
510.0
757.9
937.4
15
457170
627995
830250
937.4
777.6
985.4
18
466665
707605
978812
580.3
810.8
1015.2
20
518180
713780
1049600
602.0
805.3
1006.9
23
603231
802696
1103402
620.5
875.9
1072.4
25
668450
915075
1244350
660.6
905.4
1008.0
28
719057
1013297
1303392
678.6
903.3
1139.3
30
707980
1031880
1404500
705.1
987.7
1068.7
33
844143
1189408
1508782
766.7
1043.0
1215.7
35
846770
1264195
1710050
795.6
1052.4
1248.9
38
988489
1301029
1809572
800.8
1145.1
1251.6
40
1034820
1462020
1981000
872.1
1189.3
1338.6
43
1102095
1538160
2105762
920.8
1209.4
1397.1
45
1142130
1675355
2277350
914.5
1308.5
1437.9
48
1294961
1780801
2407352
1006.7
1336.0
1472.1
50
1308700
1904200
2599100
1042.8
1440.1
1546.8Furthermore, we have to look at the following affect in CPU time difference. Here DWVS-DD size is described by working service station size. The CUP time difference for different DWVS-DD size is described in Table1.Using polynomial curve fitting to the OPT data can provide good results. The results are shown in Figure7. Referring to the results obtained by using the PM-PCP program for RM-SPIP and RM-DPIDP model, we observe that the quality of the OPT value is improved. In comparison, the performance of PM-PCP program for RM-SPIP and RM-DPIDP is very significant when the scale of the problem becomes relatively large.Figure 7
Fitting curve of OPT for 3 models.Furthermore, using polynomial curve fitting to the CUP time data can also provide good results. The results are displayed in Figure8. In comparison, along with the increase in scale of the problem, CPU time of PM-PCP program for RM-SPIP and RM-DPIDP slightly increases.Figure 8
Fitting curve of CUP time for 3 models.


## 8. Conclusions

In this paper, a mixed integer programming model has been developed for DWVS-DD. Instead of a large integer program, the problem is decomposed into small local problems that are guided by preset control parameters. The preset control parameters result in decoupling the local problems for different time periods. Then we propose two types of preset control parameters, namely, single preset control parameters (SPCP) and double preset control parameters (DPCP). By introducing them into the MIP model, the models are then reformulated as a piecewise form, namely, RM-SPIP and RM-DPIDP. According to the specific structure of the RM-SPIP and RM-DPIDP, piecewise method by updating preset control parameters (PM-PCP) is developed.The primary goal of this paper is to set up a new model of the DWVS-DD and solve it in an effective and efficient way. Tests have been conducted to examine the performance of the PM-PCP program for the proposed new model.Future research can focus on multiple vehicle and service types. The assumption of multiple vehicle and service types adds considerable complexity to the problem of DWVS-DD. In spite of this, we have shown that the PM-PCP approach can handle very big problems and provide high-quality integer solutions.



---

*Source: 7217309-2017-10-22.xml*