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#### A multi-product multi-period inventory control problem under inflation and discount: A parameter-tuned particle swarm optimization algorithm

, Article International Journal of Advanced Manufacturing Technology ; Vol. 70, issue. 9-12 , 2014 , pp. 1739-1756 ; ISSN: 02683768 ; Hajipour, V ; Niaki, S. T. A ; Aalikar, N ; Sharif University of Technology
Abstract

In this paper, a seasonal multi-product multi-period inventory control problem is modeled in which the inventory costs are obtained under inflation and all-unit discount policy. Furthermore, the products are delivered in boxes of known number of items, and in case of shortage, a fraction of demand is considered backorder and a fraction lost sale. Besides, the total storage space and total available budget are limited. The objective is to find the optimal number of boxes of the products in different periods to minimize the total inventory cost (including ordering, holding, shortage, and purchasing costs). Since the integer nonlinear model of the problem is hard to solve using exact methods, a...

#### A constrained multi-product pricing and inventory control problem

, Article Applied Soft Computing Journal ; Volume 12, Issue 8 , 2012 , Pages 2454-2461 ; 15684946 (ISSN) ; Mahlooji, H ; Nosratian, N. E ; Sharif University of Technology
Elsevier
2012

Abstract

The aim of this article is presenting a new constrained multi-product pricing and inventory model in which perishable products are put into three categories: substitute, complementary and independent. The general demand is found by considering the relations of different products and the impact of their prices. The goal of the model is deciding on the prices as well as the inventory and production decisions in order to maximize the total profit. The derived model is a non-linear programming model and a genetic algorithm is developed for its solution. To enhance the performance of our genetic algorithm, we apply the Taguchi experimental design method to tune the parameters of the algorithm....

#### Optimizing multiproduct multiconstraint inventory control systems with stochastic period length and emergency order

, Article Journal of Uncertain Systems ; Volume 7, Issue 1 , 2013 , Pages 58-71 ; 17528909 (ISSN) ; Niaki, S.T.A ; Naini, G. J ; Sharif University of Technology
2013

Abstract

While the usual assumptions in multiperiodic inventory control problems are that the orders are placed either at the beginning of each period (periodic review) or depending on the inventory level they can happen at any time (continuous review), in this paper we assume the periods between two replenishments of several products are identical and independent random variables. For the problem at hand, the order quantities (decision variables) are of integertype and there are two kinds of space and service level constraints for each product. A model of the problem is first developed in which a combination of backorder and emergency orders is considered for the shortages, and the costs are...

#### A two-echelon single-period inventory control problem with market strategies and customer satisfaction

, Article Journal of Uncertain Systems ; Volume 11, Issue 1 , 2017 , Pages 18-34 ; 17528909 (ISSN) ; Akhavan Niaki, S. T ; Keshavarzi, A ; Sharif University of Technology
World Academic Union
2017

Abstract

In this research, a single-period two-echelon inventory control problem with market targeting strategies is considered. In this problem, there are several final products and raw materials with varying usage rates. The objective is to determine the order sizes of final products and raw materials before the selling period such that customers' satisfaction is reached and expected profit is maximized within an available budget. The problem is first mathematically formulated and then a modified particle swarm optimization algorithm is employed to solve the nonlinear programming problem. To validate the results obtained, a simulated annealing algorithm is provided as a benchmark. The parameters of...

#### Multi-product multi-constraint inventory control systems with stochastic replenishment and discount under fuzzy purchasing price and holding costs

, Article American Journal of Applied Sciences ; Volume 6, Issue 1 , 2009 , Pages 1-12 ; 15469239 (ISSN) ; Akhavan Niaki, S. T ; Aryaneznad, M. B ; Sharif University of Technology
2009

Abstract

While in multi-periodic inventory control problems the usual assumption are that the orders are placed at the beginning of each period (periodic review) or depending on the inventory level they can happen at any time (continuous review), in this research, we relax these assumptions and assume that the periods between two replenishments of the products are independent and identically distributed random variables. Furthermore, assuming the purchasing price are triangular fuzzy variables, the quantities of the orders are of integer-type and that there are space, budget and service level constraints, incremental discount is considered to purchase products and a combination of back-order and...

#### Optimization of Supply Chains Inventory System Controlled by Kanban

, M.Sc. Thesis Sharif University of Technology ; Akbari, Mohammad Reza (Supervisor)
Abstract

Kanban inventory system has been applied as a tool of implementing lean production and just in time philosophy since three decades ago. By implementing kanban in supply chain which consist of suppliers , producers , distributors and consumers, real information of demands transfers upstream and materials flows downstream and integrated supply chain can be optained. Therefore a lot of mathematical models for optimizing kanban inventory system in supply chain has been developed to implement just in time philosophy and reduce total inventory cost in supply chain systems this research consist of two main section. In the first section , kanban and supply chain primary concepts are reviewed and...

#### A two-echelon single-period inventory control problem under budget constraint

, Article International Journal of Advanced Manufacturing Technology ; Volume 56, Issue 9-12 , 2011 , Pages 1205-1214 ; 02683768 (ISSN) ; Niaki, S. T. A ; Rashidi, R ; Sharif University of Technology
Abstract

This paper points out an application of the "two-echelon single-period product (newsboy) problem," in which within a limited budget the final product and the raw materials are purchased before the start of the selling period and depending on the demand, the raw materials may be transformed into the finished product during the period. The objective of this problem is to find the order quantities of both the raw materials and the final product at the beginning of the period such that the expected profit is maximized. A new model is first developed for this problem and then a Lagrangian method is proposed to solve it. Finally, a numerical example is given to illustrate the application of the...

#### Vendor's optimal inventory policy with dynamic and discrete demands in an infinite time horizon

, Article Computers and Industrial Engineering ; Volume 102 , 2016 , Pages 368-373 ; 03608352 (ISSN) ; Haji, A ; Haji, R ; Sharif University of Technology
Elsevier Ltd
2016

Abstract

Although inventory control under discrete demand in dynamic quantities and time intervals are very common in reality, existing literature has largely ignored them. In this paper, we investigate the inventory control decisions in a two echelon supply chain consisting of one vendor and several retailers. The vendor supplies a product to several retailers, who buy discrete quantities in pre-determined time intervals. The order quantity and order cycles for each retailer can be different from others. Vendor orders the required quantity from supplier and it will be immediately received at the vendor's warehouse. In this system, shortage is not allowed for the vendor. The transportation time from...

#### A hybrid imperialist competitive-simulated annealing algorithm for a multisource multi-product location-routing-inventory problem

, Article Computers and Industrial Engineering ; Volume 101 , 2016 , Pages 116-127 ; 03608352 (ISSN) ; Akbari jokar, M. R ; Sharif University of Technology
Elsevier Ltd

Abstract

This article studies a multi-product and multi-period location-routing-inventory problem in which location-allocation, inventory and routing decisions are to be taken in a three-level supply chain including suppliers, depots and customers. Products are distributed from depots to customers by a homogeneous fleet of vehicles. Backlogging is allowable on condition that the backlog quantity of each customer does not exceed a predefined fraction of his demand. A mixed-integer programming formulation is presented to describe the problem then a new hybrid heuristic algorithm based on the simulated annealing and imperialist competitive algorithm is designed to solve the model. Comprehensive...

#### A bi-objective inventory optimization model under inflation and discount using tuned Pareto-based algorithms: NSGA-II, NRGA, and MOPSO

, Article Applied Soft Computing Journal ; Volume 43 , 2016 , Pages 57-72 ; 15684946 (ISSN) ; Sadeghi, J ; Akhavan Niaki, S. T ; Tavana, M ; Sharif University of Technology
Elsevier Ltd

Abstract

This study presents a seasonal multi-product multi-period inventory control model with inventory costs obtained under inflation and all-unit discount policy. The products are delivered in boxes of known quantities and both backorder and lost-sale quantities are considered in case of shortage. The goal is to find a representative set of Pareto optimal solutions (including the ordering quantities) in different periods and to minimize both the total inventory cost (i.e. ordering, holding, shortage, and purchasing costs) and the total storage space, simultaneously. Three multi-objective optimization algorithms of non-dominated sorting genetic algorithm (NSGA-II), non-dominated ranked genetic...

#### Optimizing multi-product multi-constraint inventory control systems with stochastic replenishments

, Article Journal of Applied Sciences ; Volume 8, Issue 7 , 2008 , Pages 1228-1234 ; 18125654 (ISSN) ; Aryanezhad, M. B ; Akhvan Niaki, S. T ; Sharif University of Technology
Asian Network for Scientific Information
2008

Abstract

Multi-periodic inventory control problems are mainly studied employing two assumptions. The first is the continuous review, where depending on the inventory level orders can happen at any time and the other is the periodic review, where orders can only happen at the beginning of each period. In this study, we relax these assumptions and assum that the periodic replenishments are stochastic in nature. Furthermore, we assume that the periods between two replenishments are independent and identically random variables. For the problem at hand, the decision variables are of integer-type and there are two kinds of space and service level constraints for each product. We develop a model of the...

#### Queueing with Inventory Models for Analysing Make-to-Order Systems

, Ph.D. Dissertation Sharif University of Technology ; Hajji, Alireza (Supervisor)
Abstract

In this thesis, we consider various Make-to-Order systems as a version of integrated production-inventory systems. Most Make-to-order systems can be sufficiently modeled by a queueing system with inventory in which completing each service in the queueing system requires an on-hand inventory. Unlike most researches in this field, we present an analytical approach. In all systems we embed a stochastic process with joint state space that can entirely describe the state of system. Then steady state distributions are derived. Those distributions are applied to compute performance measures and long-run average cost function which can be used for optimization. In our Make-to-Order models, demands...

#### Robust Optimization of Inventory in Supply Chain Management

, M.Sc. Thesis Sharif University of Technology ; Modarres Yazdi, Mohammad (Supervisor)
Abstract

In this research, the determination of inventory management policy is investigated in two-level supply chains. Two scenarios are considered to analyze this problem. In the first one, all parameters are assumed to be deterministic while in the other one, the retailer’s demand is assumed to be uncertain. We extend the previous studies by considering the real world conditions; and introduce a model in which the costs of lost-sale and backorder are considered simultaneously. A genetic algorithm is developed to solve the proposed model. To evaluate the efficiency of the model, the results are compared over five different examples when only complete backorder is considered. In case of uncertain...

#### Optimization of Blood Supply Chain

, M.Sc. Thesis Sharif University of Technology ; Kianfar, Farhad (Supervisor)
Abstract

Blood is a perishable product and can only be stored for a limited time. Reducing the level of wastage and shortage in supply chain of blood products is the main challenge of supply chain management. Wastage occurs whenever hospitals and blood banks order excessive blood while ordering insufficient amount results in shortage. Wastage can increase the costs in supply chain while shortage can cause important operation to be cancelled.This thesis presents an integer programming model for improving blood related operations in hospitals and blood banks. The presented model determines optimal order levels for each period which minimize total cost, shortage and wastage levels. The model is...

#### Two metaheuristics to solve a multi-item multiperiod inventory control problem under storage constraint and discounts

, Article International Journal of Advanced Manufacturing Technology ; Volume 69, Issue 5-8 , 2013 , Pages 1671-1684 ; 02683768 (ISSN) ; Niaki, S. T. A ; Mousavi, S. M ; Sharif University of Technology
2013

Abstract

In this paper, a multi-item multiperiod inventory control problem with all-unit and/or incremental quantity discount policies under limited storage capacity is presented. The independent random demand rates of the items in the periods are known and the items are supplied in distinct batch sizes. The cost consists of ordering, holding, and purchasing. The objective is to find the optimal order quantities of all items in different periods such that the total inventory cost is minimized and the constraint is satisfied. A mixed binary integer programming model is first developed to model the problem. Then, a parameter-tuned genetic algorithm (GA) is employed to solve it. Since there is no...

#### Multiproduct EPQ model with single machine, backordering and immediate rework process

, Article European Journal of Industrial Engineering ; Volume 5, Issue 4 , 2011 , Pages 388-411 ; 17515254 (ISSN) ; Sadjadi, S. J ; Niaki, S. T. A ; Sharif University of Technology
Abstract

Production systems with scrapped and rework items have recently become an interesting subject of research. While most attempts have been focused on finding the optimal production quantity in a simple production system, little work appears on a joint production environment. In this research, two joint production systems in a form of multiproduct single machine with and without rework are studied where shortage is allowed and backordered. For each system, the optimal cycle length, the backordered and production quantities of each product are determined such that the cost function is minimised. Proof of the convexity of the involved objective functions of each model is provided and numerical...

#### A parameter-tuned genetic algorithm for multi-product economic production quantity model with space constraint, discrete delivery orders and shortages

, Article Advances in Engineering Software ; Volume 41, Issue 2 , 2010 , Pages 306-314 ; 09659978 (ISSN) ; Niaki, S.T.A ; Yeganeh, J. A ; Sharif University of Technology
2010

Abstract

In this paper, a multi-product economic production quantity problem with limited warehouse-space is considered in which the orders are delivered discretely in the form of multiple pallets and the shortages are completely backlogged. We show that the model of the problem is a constrained non-linear integer program and propose a genetic algorithm to solve it. Moreover, design of experiments is employed to calibrate the parameters of the algorithm for different problem sizes. At the end, a numerical example is presented to demonstrate the application of the proposed methodology

#### A genetic algorithm approach to optimize a multi-products EPQ model with discrete delivery orders and constrained space

, Article Applied Mathematics and Computation ; Volume 195, Issue 2 , 2008 , Pages 506-514 ; 00963003 (ISSN) ; Akhavan Niaki, S. T ; Sharif University of Technology
2008

Abstract

The economic production quantity (EPQ) is one of the most applicable model in production and inventory control environments. Like other classical production and inventory control models, it is derived based upon assumptions that cause limited real-world applications. Continuous and constant-rate delivery of orders, infinite availability of warehouse spaces, and applicability on a single product are some of these assumptions. In order to make the EPQ model more applicable to real-world production and inventory control problems, in this paper, we expand this model by assuming that the orders may be delivered discretely in the form multiple pallets. In addition, we may have more than one...

#### Optimal solution for a two-level inventory system with information exchange leading to a more computationally efficient search

, Article Applied Mathematics and Computation ; Volume 189, Issue 2 , 2007 , Pages 1341-1349 ; 00963003 (ISSN) ; Haji, R ; Sharif University of Technology
2007

Abstract

In this paper we consider a two-level inventory system with one warehouse and one retailer with information exchange. The retailer applies fixed order size continuous review policy. The supplier starts with m initial batches of the same order size of the retailer, and places an order to an outside source immediately after the retailer's inventory position reaches an amount equal to the retailer's order point plus a fixed value s. Transportation times are constant and the retailer faces independent Poisson demand. In a recent paper it was pointed out that the optimal supplier policy in this inventory system is an open question. To obtain the optimal policy for this system, first we find the...

#### The single period problem with price discount and probabilistic initial inventory

, Article 2006 IIE Annual Conference and Exposition, Orlando, FL, 20 May 2006 through 24 May 2006 ; 2006 ; Haji, M ; Sharif University of Technology
2006

Abstract

In this paper we consider a newsvendor problem in which the suppliers offer quantity discounts. We assume that the initial inventory at the beginning of the period is a random variable. This assumption, among other applications, may apply to the case where the decision about the order quantity must be made at a time long before the start of the period and the available inventory may decrease due to several factors, such as deterioration, consumption, etc. up to the start of the period. In this paper, we obtain the optimal order quantity that maximizes the total profit for this model