Mathematical Problems in Engineering

Volume 2017, Article ID 3920327, 11 pages

https://doi.org/10.1155/2017/3920327

## The Improved Ant Colony Optimization Algorithm for MLP considering the Advantage from Relationship

School of Mechanical and Electronic Engineering, Wuhan University of Technology, Wuhan City 430070, China

Correspondence should be addressed to Yabo Luo; moc.361@3791obayoul

Received 27 December 2016; Revised 27 March 2017; Accepted 4 June 2017; Published 31 July 2017

Academic Editor: Gen Q. Xu

Copyright © 2017 Yabo Luo and Yongo P. Waden. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

An improved ant colony optimization (ACO) is presented to solve the machine layout problem (MLP), and the concept is categorized as follows: firstly, an ideology on “advantage from quantity” and “advantage from relationship” is proposed and an example is demonstrated. In addition, the strategy of attached variables under local polar coordinate systems is employed to maintain search efficiency, that is, “advantage from relationship”; thus, a mathematical model is formulated under a single rectangular coordinate system in which the relative distance and azimuth between machines are taken as attached design variables. Further, the aforementioned strategies are adopted into the ant colony optimization (ACO) algorithm, thereby employing the inverse feedback mechanism for dissemination of pheromone and the positive feedback mechanism for pheromone concentration. Finally, the effectiveness of the proposed improved ACO is tested through comparative experiments, in which the results have shown both the reliability of convergence and the improvement in optimization degree of solutions.

#### 1. Introductions

A machine layout problem (MLP) is categorized under a quadratic assignment problem (QAP) which is known as NP-hard and unsolvable with traditional optimization methods [1, 2]. Thus, bionic algorithms which mimic the principles or behaviors of living organisms to achieve optimization in an objective function, have achieved some progress in solving MLP [3, 4]. For instance, Samarghandi and Eshghi [5] proposed a new method based on tabu search for a single row facility layout problem (SRFLP) and they have reported better solutions than other methods in the literature. Further, Selvakumar et al. were able to optimize the equipment layout by employing an improved artificial neural network [6]. Meanwhile, GA improvements, such as in the permutation-based [7] and the reverse constraint satisfied tactics [8], have been applied to determine the optimal solutions as well. Further, the application of swarm intelligence such as artificial bee colony (ABC) [9–11], Particle Swarm Optimization (PSO) [12, 13], and the ACO [14, 15] have contributed significantly to solving combinatorial problems. Nevertheless, literature is widely dominated by applications of the swarm intelligence in tackling MLP, especially, the ACO [16]. Ulutas and Kulturel-Konak [17] have indicated that research in MLP is most significant and fruitful.

Notwithstanding all the progress in solving MLP, however, majority of the research concentrates on the small-size and standardized problems, which are mainly focused on linear placement of rectangular facilities with varying dimensions on some straight lines such as the single row [18] and double row layout [19]. Although few researchers tried to solve the multiline and flexible layout problems [20, 21], search efficiency and convergence cannot be guaranteed. As pointed out in [22] satisfactory solutions to large-scale problems are difficult to obtain. In addition, as far as the literature is concerned, no research existed on exploring the reasons of inefficiency in convergence and search in the large instance of MLP, except some attempts by Drira et al. [23] and Saravanan and Arulkumar [24]. Therefore, research on MLP under a flexible manufacturing environment with minimum constraints is still in a primary stage. As based on the analysis of the key reasons for the inefficiency of search and poor convergence, this research proposes a novel approach that transforms the coordinate system for design variables and constraint space to local polar coordinate systems. Thereby, ACO algorithm is improved by incorporating the novel approach, in order to optimize the problem of inefficiency in convergence and search strategy in the ACO.

#### 2. “Advantage from Quantity” and “Advantage from Relationship”

From optimization perception, two kinds of advantages, named “advantage from quantity” and “advantage from relationship” [25], are constructed based on natural behaviors in insects, animal, or human, and, as the names sound, no such strategy has been reported in the wide literature of computational intelligence. *Advantage from Quantity*. It means an advantage usually comes from the quantity of a certain property, which is contingent on the measurement of a certain value. For example, the loading capacity of a lorry depends on its volume; the viability of a giraffe depends on the length of its neck; the survival chance of a locust depends on its similarity in color with grass. Consequently, these examples, the volume, length, and the degree of a certain property are all advantages from quantity. *Advantage from Relationship*. It is from a relationship, which is not contingent on the independent features of properties but on the relationship among them; for example, the equilibrium of a plane lies not on the independent loading capacity of the front cabin, middle cabin, or the rear cabin but on proportion of them, and the balance of a dragonfly lies not in the weight of the head or the independent value of the length of torso but in the ratio between them. Therefore, from these examples, advantages are contingent on the relationship among properties and, thus, belong to the advantage from relationship.

Furthermore, the major difference between the two kinds of advantages is that the advantage from quantity is convergent in a normal bionic algorithm whereas the advantage from relationship is not, because distribution of values in the feasible regions of these two advantages is quite different. Hence, the differences can be illustrated by examples as follows.

*Example 1. *Let us determine the values of , , and :From the genetic algorithm, binary design variables are defined as follows:where , and then , , and

If the coding method above is adopted and run in 10 iterations, numerous individuals in the population can be updated as , whereby the optimal individuals are , , and . Further, if the coding is run 20 times of iterations, all individuals are updated to their optimal position and also stability is maintained.

*Example 2. *Let us find the values of , , and whereAgain if genetic algorithm principle is adopted, the search efficiency is low, because of the variant factors involved; additionally, the optimal population cannot be maintained because the solution space takes on a status of divergence in further iterations.

The reason for difference can be seen in Example 1, a problem with “advantage from quantity” which has a feasible region with a good property though is monotonic. Moreover, the population formed by fit individuals that are more capable of generating fitted offspring, as such, is shown by the following.

Let us assume thatHence, from (4), individuals and are better than and , where their offspring have high possibility of achieving better fitness compared to those from and . Therefore, the search process of problem with “advantage from quantity” is convergent and the optimized population is stable. On the contrary, as is seen in Example 2, a problem with “advantage from relationship,” where the offspring produced by fitted parents are not better than those produced by random individuals in the feasible region, is shown below: The individuals and are optimal; meanwhile, individuals and are not optimal, but, after crossover operations, individuals updated by and are not optimal whereas those updated by and are likely to be optimal individuals. In addition, for a population formed by fit individuals, those having “advantage from relationship” do not necessarily have to be fit to generate fit offspring, hence, that can lead to inefficiency in convergence and search process.

A machine layout problem (MLP) is a typical problem, with “advantage from relationship.” That is, the efficiency of materials flow (logistic) in the machines is not contingent on the independent locations of each machine but on the relationship among them. Further, inefficiency in logistics can be realized still, if a rectangular coordinate system is considered for the logistic in MLP, where the coordinates of locations for machines are changed but relative positions relationships are maintained. On the contrary, efficiency in logistics can be increased if the locations of few machines are changed; meanwhile, other locations of machines are kept still. Therefore, the interaction between the locations of machines and the efficiency in logistics cannot be illustrated by considering rectangular coordinates of machines as design variables only but also by controlling the design variables in order to illustrate the relationship of the relative positions of machines.

#### 3. Basic MLP Model under Rectangular Coordinate System

A MLP can be described as follows: machines are arranged in a workshop with the dimensions such as length and width . And each geometry of a machine is denoted by a rectangular box whereby and are represented by and , respectively. In addition, the objective function is a minimization of the total cost of material flow in the machines under geometric constraint of the workspace, where the geometric description of workshop is shown in Figure 1.