References of "Rezaei Sadrabadi, Mahmood"
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See detailInventory routing for perishable products
Rezaei Sadrabadi, Mahmood ULg

Doctoral thesis (2016)

We explore three problems in this thesis and develop solution methods for each problem. First, an inventory routing problem for a perishable product with stochastic demands is considered and different ... [more ▼]

We explore three problems in this thesis and develop solution methods for each problem. First, an inventory routing problem for a perishable product with stochastic demands is considered and different approximate solution methods are developed to solve. Based on computational experiments, the solution methods are compared in terms of average profit, service level, and actual freshness. The impact of relevant parameters on the performance of the solution methods is investigated. Managerial insights are drawn by analyzing the impact of shelf life and store capacity on the profit. The value of considering uncertainty and the value of accessing full information are measured. The computational results highlight that a simple ordering policy can often replace a more sophisticated solution method, while preserving the same efficacy. Second, we introduce a vehicle routing problem (VRP) where a set of stores places deterministic orders to a logistics service provider (LSP) for two successive periods. Deliveries requested in each period can be shifted by the LSP to the other period, possibly with modified quantities. The LSP incurs a penalty for any diversion from the initial delivery period. The data regarding shifted delivery quantities and penalties are provided by the stores. From the perspective of the LSP, diversions could be beneficial if savings in the routing costs outweigh the penalties. In this work, we introduce a new two-period VRP model where the LSP seeks to improve its total cost, compared to solving two independent VRPs with fixed delivery periods, by allowing deliveries to be shifted. We solve this model to optimality by an efficient branch-and-price algorithm implementing several cutting-edge techniques. We draw algorithmic and managerial insights based on our test instances. Third, a two-period VRP is considered where the orders placed by stores for each period can be partially shifted to the other period, given that the sum of the delivery quantities in two periods to each customer is fixed. A linear penalization of delivery shifts is assumed based on the quantity shifted. We represent two mixed integer linear programming (MILP) formulations for the problem. A column-row generation algorithm to solve the LP-relaxation of the first formulation is developed. To solve the LP-relaxation of the second formulation, we develop a column generation algorithm. Details of two label-setting algorithms to solve the pricing problems of the column-row generation and column generation algorithms are discussed. Numerical results can be compared with a similar model in which only full delivery shifts are allowed. [less ▲]

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See detailA branch-and-price algorithm for 2-period vehicle routing problems
Crama, Yves ULg; Rezaei Sadrabadi, Mahmood ULg; Van Woensel, Tom

E-print/Working paper (2015)

We consider a Vehicle Routing Problem (VRP) with deterministic orders in two periods from a set of stores. Orders in period 1 (2) can be postponed (advanced) to the other period but any diversion from the ... [more ▼]

We consider a Vehicle Routing Problem (VRP) with deterministic orders in two periods from a set of stores. Orders in period 1 (2) can be postponed (advanced) to the other period but any diversion from the initial orders incurs a penalty. From the perspective of a Logistics Service Provider (LSP), such diversions could be beneficial if savings in the routing costs outweigh the penalties. So could they be from a store's view, as the store can set a high enough penalty to compensate the diversion from its own optimal orders. In this paper, we introduce a new model where we seek a better solution for the LSP, compared to solving two independent VRPs with fixed orders, by allowing orders to be fully postponed or advanced. We apply a branch-and-price algorithm to solve this model to optimality. Many cutting-edge techniques are implemented to have an efficient branch-and-price algorithm, and two ideas to possibly improve the upper bound are tested. We draw algorithmic and managerial insights based on our test instances. [less ▲]

Detailed reference viewed: 127 (8 ULg)
See detailBranch-and-price: principles and its application to a 2-period vehicle routing problem
Rezaei Sadrabadi, Mahmood ULg

Scientific conference (2013, April 05)

We review branch-and-price as an efficient algorithm to solve integer programming problems with huge number of variables. In particular, we discuss column generation algorithm as the main engine in branch ... [more ▼]

We review branch-and-price as an efficient algorithm to solve integer programming problems with huge number of variables. In particular, we discuss column generation algorithm as the main engine in branch-and-price. Implementation of branch-and-price to solve the most basic version of the well-known vehicle routing problem (VRP) is investigated, and some common tricks are introduced. Then, a new extension of VRP is introduced and exploitation of branch-and-price to solve it is discussed. We consider a 2-period vehicle routing problem where each vertex of the network has a positive demand for period 1, 2, or both. Each demand on period 1 can be postponed to period 2 in order to decrease sum of the routing costs on two periods, but it is penalized in the objective function. Similarly, each demand on period 2 can be advanced to period 1, and yet penalized, with the hope of reducing routing costs. We have used many of the classic tricks to implement branch-and-price for solving our 2-period VRP. We have also used new tricks to (1) possibly improve the upper bound during the course of column generation in each node and (2) decrease the computations time to solve pricing problem in column generation. [less ▲]

Detailed reference viewed: 47 (1 ULg)
See detailBranch-and-price: principles and its application to a 2-period vehicle routing problem
Rezaei Sadrabadi, Mahmood ULg

Scientific conference (2013, April 05)

We review branch-and-price as an efficient algorithm to solve integer programming problems with huge number of variables. In particular, we discuss column generation algorithm as the main engine in branch ... [more ▼]

We review branch-and-price as an efficient algorithm to solve integer programming problems with huge number of variables. In particular, we discuss column generation algorithm as the main engine in branch-and-price. Implementation of branch-and-price to solve the most basic version of the well-known vehicle routing problem (VRP) is investigated, and some common tricks are introduced. Then, a new extension of VRP is introduced and exploitation of branch-and-price to solve it is discussed. We consider a 2-period vehicle routing problem where each vertex of the network has a positive demand for period 1, 2, or both. Each demand on period 1 can be postponed to period 2 in order to decrease sum of the routing costs on two periods, but it is penalized in the objective function. Similarly, each demand on period 2 can be advanced to period 1, and yet penalized, with the hope of reducing routing costs. We have used many of the classic tricks to implement branch-and-price for solving our 2-period VRP. We have also used new tricks to (1) possibly improve the upper bound during the course of column generation in each node and (2) decrease the computations time to solve pricing problem in column generation. [less ▲]

Detailed reference viewed: 20 (1 ULg)
See detailBranch-and-price: principles and its application to a 2-period vehicle routing problem
Rezaei Sadrabadi, Mahmood ULg

Scientific conference (2013, March 07)

We review branch-and-price as an efficient algorithm to solve integer programming problems with huge number of variables. In particular, we discuss column generation algorithm as the main engine in branch ... [more ▼]

We review branch-and-price as an efficient algorithm to solve integer programming problems with huge number of variables. In particular, we discuss column generation algorithm as the main engine in branch-and-price. Implementation of branch-and-price to solve the most basic version of the well-known vehicle routing problem (VRP) is investigated, and some common tricks are introduced. Then, a new extension of VRP is introduced and exploitation of branch-and-price to solve it is discussed. We consider a 2-period vehicle routing problem where each vertex of the network has a positive demand for period 1, 2, or both. Each demand on period 1 can be postponed to period 2 in order to decrease sum of the routing costs on two periods, but it is penalized in the objective function. Similarly, each demand on period 2 can be advanced to period 1, and yet penalized, with the hope of reducing routing costs. We have used many of the classic tricks to implement branch-and-price for solving our 2-period VRP. We have also used new tricks to (1) possibly improve the upper bound during the course of column generation in each node and (2) decrease the computations time to solve pricing problem in column generation. [less ▲]

Detailed reference viewed: 21 (1 ULg)
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Peer Reviewed
See detailA heuristic method to schedule training programs for Small and Medium Enterprises
Rezaei Sadrabadi, Mahmood ULg; Shamsaei, Fahimeh; Mohammadian, Iman et al

in European Journal of Operational Research (2012), 217

During the life period of Small and Medium Enterprises (SMEs) in incubators they need some training programs to acquire the required knowledge in order to survive and succeed in the business environment ... [more ▼]

During the life period of Small and Medium Enterprises (SMEs) in incubators they need some training programs to acquire the required knowledge in order to survive and succeed in the business environment. This paper presents a heuristic method based on an optimization model to schedule these programs at the most suitable times. Based on the proposed heuristic, each training program is implemented in a suitable time by considering the SMEs’ requirements and some other logical constraints. The proposed heuristic is described in detail, and its implementation is demonstrated via a real-life numerical example. The numerical results of the heuristic are compared with other methods. [less ▲]

Detailed reference viewed: 83 (9 ULg)
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Peer Reviewed
See detailIdentification of the linear parts of nonlinear systems for fuzzy modeling
Rezaei Sadrabadi, Mahmood ULg

in Applied Soft Computing (2011), 11

In direct approach to fuzzy modeling, structure identification is one of the most critical tasks. In modeling the nonlinear system, this fact is more crucial. In this paper, a new hybrid method is ... [more ▼]

In direct approach to fuzzy modeling, structure identification is one of the most critical tasks. In modeling the nonlinear system, this fact is more crucial. In this paper, a new hybrid method is proposed to cluster the data located in the linear parts on the nonlinear systems. The proposed method can partition the input–output data in two groups: data located in the linear parts and data in the extrema. It is shown that the first group of data is suitable to be clustered by Fuzzy C-Regression Model (FCRM) clustering algorithm and the second group by Fuzzy C-Means (FCM). Then, based on the above findings, a new hybrid clustering algorithm is proposed. Finally, the proposed approach is tested and validated by several numerical examples of nonlinear functions. [less ▲]

Detailed reference viewed: 62 (30 ULg)
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Peer Reviewed
See detailFacility location via fuzzy modeling and simulation
Rezaei Sadrabadi, Mahmood ULg; Fazel Zarandi, M. H.

in Applied Soft Computing (2011), 11(8), 5330-5340

This paper presents a continuous facility location model with fuzzy methodology. The developments concern mainly to some drawbacks in the initial model which takes it far from being used in practice. A ... [more ▼]

This paper presents a continuous facility location model with fuzzy methodology. The developments concern mainly to some drawbacks in the initial model which takes it far from being used in practice. A fuzzy modeling method is proposed to estimate the required functions in the initial model. Structure identification in the proposed fuzzy modeling method is carried out using subtractive clustering, and parameter identification is conducted via some heuristics as well as an optimization problem. Furthermore, a simulation method along with some heuristic relations is used for implementation and evaluation of the modified model. Efficiency of the proposed method to fuzzy modeling as well as the proposed simulation method is presented by a numerical example. [less ▲]

Detailed reference viewed: 194 (21 ULg)
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Peer Reviewed
See detailA new method to fuzzy modeling and its application in performance evaluation of tenants in incubators
Rezaei Sadrabadi, Mahmood ULg

in International Journal of Advanced Manufacturing Technology (2008), 37

As we know fuzzy modeling is one of the most powerful techniques to extract experts’ knowledge in the form of fuzzy if-then rules. In this research work, a new method to fuzzy modeling is proposed in ... [more ▼]

As we know fuzzy modeling is one of the most powerful techniques to extract experts’ knowledge in the form of fuzzy if-then rules. In this research work, a new method to fuzzy modeling is proposed in which the main goal is to construct a fuzzy rule-base of the type of Mamdani. In the proposed method, fuzzy c-means (FCM) clustering is used for structure identification and two optimization problems are used for parameter identification. The proposed method is used to simulate experts’ knowledge for performance evaluation of tenants in incubators. The authors have implemented their proposed method in a real numerical example successfully. [less ▲]

Detailed reference viewed: 34 (4 ULg)