Population-based Heuristic Algorithm Research Articles

Heuristic and swarm intelligence algorithms for work-life balance problem

Employee satisfaction significantly influences the success of business. This emphasises on the importance of employees managing their work, family and personal lives to maintain their physical and mental well-being. This is especially crucial in health-care sector, where physical and mental well-being directly affects the quality of out-coming services provided. Work-life balance, defined as the challenge of striking a reasonable equilibrium between work, family, and personal life, is gaining more attention. However, many studies do not adequately consider employee preferences when addressing this issue. This study introduces a mathematical model for work-life balance problem prioritising the worker preferences focusing on healthcare workers as a special case where personnel preferences are integrated into decision-making. The model has been comparatively solved with population-based algorithms for optimising weekly personnel schedules in order to make them more suitable for work-life balance. The population-based heuristic algorithms used for optimising the schedules are swarm intelligence algorithms; namely ant colony and particle swarm optimisation algorithms. The proposed approach allows the employees to opt their working hours and periods in the work-place, flexibly. We demonstrated with comparative analysis that the produced results with swarm intelligence algorithms evidently outperform one of the state-of-art works done with genetic algorithms, which proves the strength of the proposed problem solvers.

Competitive Coevolution-Based Improved Phasor Particle Swarm Optimization Algorithm for Solving Continuous Problems

Particle swarm optimization (PSO) is a population-based heuristic algorithm that is widely used for optimization problems. Phasor PSO (PPSO), an extension of PSO, uses the phase angle θ to create a more balanced PSO due to its increased ability to adjust the environment without parameters like the inertia weight w. The PPSO algorithm performs well for small-sized populations but needs improvements for large populations in the case of rapidly growing complex problems and dimensions. This study introduces a competitive coevolution process to enhance the capability of PPSO for global optimization problems. Competitive coevolution disintegrates the problem into multiple sub-problems, and these sub-swarms coevolve for a better solution. The best solution is selected and replaced with the current sub-swarm for the next competition. This process increases population diversity, reduces premature convergence, and increases the memory efficiency of PPSO. Simulation results using PPSO, fuzzy-dominance-based many-objective particle swarm optimization (FMPSO), and improved competitive multi-swarm PPSO (ICPPSO) are generated to assess the convergence power of the proposed algorithm. The experimental results show that ICPPSO achieves a dominating performance. The ICPPSO results for the average fitness show average improvements of 15%, 20%, 30%, and 35% over PPSO and FMPSO. The Wilcoxon statistical significance test also confirms a significant difference in the performance of the ICPPSO, PPSO, and FMPSO algorithms at a 0.05 significance level.

A novel variational inequality approach for modeling the optimal equilibrium in multi-tiered supply chain networks

We present a novel variational inequality model (VIM) to capture the complex real decision-making process in multi-tiered supply chain networks (MSCN) without strictly limiting the features of related functions. The VIM is formulated with the equilibrium conditions on links as the optimization goal and the flow conservation condition as the main constraints. We transform the VIM into a series of equivalent Non-Linear Programming Models (NLPMs) to solve. To address this challenge, we propose a novel population-based heuristic algorithm called the Multiscale Model Learning Algorithm (MMLA). The MMLA is inspired by the learning behavior of individuals in a group and can converge to an optimal equilibrium state of the MSCN. The MMLA has two key operations: zooming in on the search field and learning search in a learning stage. The excellent performers, called medalists, are imitated by other learners. With the increase in learning stages, the learning efficiency is improved, and the searching energy is concentrated in a more promising area. We employ sixteen benchmark optimization problems and two supply chain networks to demonstrate the effectiveness of the MMLA and the rationality of the equilibrium models. The results obtained by MMLA for the NLPM show that the MMLA can solve the equilibrium model effectively, and multiple optimal equilibrium states may exist for an MSCN. The flexibility of the NLPM makes it possible to consider more complicated decision-making mechanisms in the model.

Optimization of Traffic Network Signal Durations with Heuristic Algorithm and the Effect of Number of Individuals

In the traffic network that we frequently use in our daily life, the primary demand of people has been to reduce the time they spend in traffic and to travel to the points they want to reach as quickly as possible. Developing countries want to meet this demand with the least cost in order to meet this demand. This study aims to manage the traffic network with the best times by optimizing the traffic signal durations in order to minimize the travel time for a road network chosen as a benchmark. For the optimization process, it is aimed to run a population-based heuristic algorithm with different numbers of individuals and obtain the best travel time. With the help of an open-source code traffic simulation program, which was run by modeling the benchmark road network, the received traffic data was also visually analyzed and compared. The effects of the heuristic algorithms applied with different numbers of individuals on the travel times according to the starting-destination points were examined before and after the optimization. As a result of the study, it has been observed that travel times and traffic signal times can be reduced with heuristic algorithms. Based on both numerical metrics and visual results, it has been determined that optimized traffic light durations give better results than non-optimized ones.

Staff scheduling for residential care under pandemic conditions: The case of COVID-19

The COVID-19 pandemic severely impacted residential care delivery all around the world. This study investigates the current scheduling methods in residential care facilities in order to enhance them for pandemic conditions. We first define the basic problem that addresses decisions associated with the assignment and scheduling of staff members, who perform a set of tasks required by residents during a planning horizon. This problem includes the minimization of costs associated with the salary of part-time staff members, total overtime, and violations of service time windows. Subsequently, we adapt the basic problem to pandemic conditions by considering the impacts of communal spaces (e.g., shared rooms) and a cohorting policy (classification of residents based on their risk of infection) on the spread of infectious diseases. We introduce a new objective function that minimizes the number of distinct staff members serving each room of residents. Likewise, we propose a new objective function for the cohorting policy that aims to minimize the number of distinct cohorts served by each staff member. A new constraint is incorporated that forces staff members to serve only one cohort within a shift. We present a population-based heuristic algorithm to solve this problem. Through a comparison with two benchmark solution approaches (a mathematical programme and a non-dominated archiving ant colony optimization algorithm), the superiority of the heuristic algorithm is shown regarding solution quality and CPU time. Finally, we conduct numerical analyses to present managerial implications.

Solution of asymmetric discrete competitive facility location problems using ranking of candidate locations

We address a discrete competitive facility location problem with an asymmetric objective function and a binary customer choice rule. Both an integer linear programming formulation and a heuristic optimization algorithm based on ranking of candidate locations are designed to solve the problem. The proposed population-based heuristic algorithm is specially adapted for the discrete facility location problems by using their features such as geographical distances and the maximal possible utility of candidate locations, which can be evaluated in advance. The performance of the proposed algorithm was experimentally investigated by solving different instances of the model with real data of municipalities in Spain.

A Modified Gravitational Search Algorithm for Function Optimization

Gravitational search algorithm (GSA) is a population-based heuristic algorithm, which is inspired by Newton’s laws of gravity and motion. Although GSA provides a good performance in solving optimization problems, it has a disadvantage of premature convergence. In this paper, the concept of repulsive force is introduced and the definition of exponential $Kbest$ is used in a new version of GSA, which is called repulsive GSA with exponential $Kbest$ (EKRGSA). In this algorithm, heavy particles repulse or attract all particles according to distance, and all particles search the solution space under the combined action of repulsive force and gravitational force. In this way, the exploration ability of the algorithm is improved and a proper balance between exploration and exploitation is established. Moreover, the exponential $Kbest$ significantly decreases the computational time. The proposed algorithm is tested on a set of benchmark functions and compared with other algorithms. The experimental results confirm the high efficiency of EKRGSA.

Feature Selection Using an Improved Gravitational Search Algorithm

Feature selection is an important issue in the field of machine learning, which can reduce misleading computations and improve classification performance. Generally, feature selection can be considered as a binary optimization problem. Gravitational Search Algorithm (GSA) is a population-based heuristic algorithm inspired by Newton's laws of gravity and motion. Although GSA shows good performance in solving optimization problems, it has a shortcoming of premature convergence. In this paper, the concept of global memory is introduced and the definition of exponential Kbest is used in an improved version of GSA called IGSA. In this algorithm, the position of the optimal solution obtained so far is memorized, which can effectively prevent particles from gathering together and moving slowly. In this way, the exploitation ability of the algorithm gets improved, and a proper balance between exploration and exploitation gets established. Besides, the exponential Kbest can significantly decrease the running time. In order to solve feature selection problem, a binary IGSA (BIGSA) is further introduced. The proposed algorithm is tested on a set of standard datasets and compared with other algorithms. The experimental results confirm the high efficiency of BIGSA for feature selection.

Determining the Optimal Location of Terror Response Facilities Under the Risk of Disruption

The highly strategic nature of terrorist attacks has often frustrated attempts at locating emergency response facilities. To better determine the optimal location of such facilities, we present a leader-follower game between State and Terrorist by considering facility failures. The first stage of the game allows State to make a facility location decision and facility assignment to the attacked city, while the second stage allows Terrorist to select one city to attack after observing the State's strategy. The game is translated into a minmaxmin problem, and a population-based heuristic algorithm is proposed to solve it. We evaluate the performance of both model and heuristic by using an emergency example. Our results indicate that the proposed algorithm is able to generate suitable facility location solutions, allowing us to deploy resources more efficiently during a terrorist attack to where they are needed.

Population-based heuristic algorithms for continuous and mixed discrete-continuous optimization problems

Continuous optimization problems are optimization problems where all variableshave a domain that typically is a subset of the real numbers; mixed discrete-continuousoptimization problems have additionally other types of variables, sothat some variables are continuous and others are on an ordinal or categoricalscale. Continuous and mixed discrete-continuous problems have a wide rangeof applications in disciplines such as computer science, mechanical or electricalengineering, economics and bioinformatics. These problems are also often hard tosolve due to their inherent difficulties such as a large number of variables, manylocal optima or other factors making problems hard. Therefore, in this thesis ourfocus is on the design, engineering and configuration of high-performing heuristicoptimization algorithms.We tackle continuous and mixed discrete-continuous optimization problemswith two classes of population-based heuristic algorithms, ant colony optimization(ACO) algorithms and evolution strategies. In a nutshell, the main contributionsof this thesis are that (i) we advance the design and engineering of ACO algorithms to algorithms that are competitive or superior to recent state-of-the-artalgorithms for continuous and mixed discrete-continuous optimization problems,(ii) we improve upon a specific state-of-the-art evolution strategy, the covariancematrix adaptation evolution strategy (CMA-ES), and (iii) we extend CMA-ES totackle mixed discrete-continuous optimization problems.More in detail, we propose a unified ant colony optimization (ACO) frameworkfor continuous optimization (UACOR). This framework synthesizes algorithmiccomponents of two ACO algorithms that have been proposed in the literatureand an incremental ACO algorithm with local search for continuous optimization,which we have proposed during my doctoral research. The design of UACORallows the usage of automatic algorithm configuration techniques to automaticallyderive new, high-performing ACO algorithms for continuous optimization. We alsopropose iCMAES-ILS, a hybrid algorithm that loosely couples IPOP-CMA-ES, aCMA-ES variant that uses a restart schema coupled with an increasing populationsize, and a new iterated local search (ILS) algorithm for continuous optimization.The hybrid algorithm consists of an initial competition phase, in which IPOP-CMA-ES and the ILS algorithm compete for further deployment during a secondphase. A cooperative aspect of the hybrid algorithm is implemented in the formof some limited information exchange from IPOP-CMA-ES to the ILS algorithmduring the initial phase. Experimental studies on recent benchmark functionssuites show that UACOR and iCMAES-ILS are competitive or superior to otherstate-of-the-art algorithms.To tackle mixed discrete-continuous optimization problems, we extend ACOMV and propose CESMV, an ant colony optimization algorithm and a covariance matrix adaptation evolution strategy, respectively. In ACOMV and CESMV , the decision variables of an optimization problem can be declared as continuous, ordinal, or categorical, which allows the algorithm to treat them adequately. ACOMV andCESMV include three solution generation mechanisms: a continuous optimizationmechanism, a continuous relaxation mechanism for ordinal variables, and a categorical optimization mechanism for categorical variables. Together, these mechanisms allow ACOMV and CESMV to tackle mixed variable optimization problems.We also propose a set of artificial, mixed-variable benchmark functions, which cansimulate discrete variables as ordered or categorical. We use them to automatically tune ACOMV and CESMV's parameters and benchmark their performance.Finally we test ACOMV and CESMV on various real-world continuous and mixed-variable engineering optimization problems. Comparisons with results from theliterature demonstrate the effectiveness and robustness of ACOMV and CESMVon mixed-variable optimization problems.Apart from these main contributions, during my doctoral research I have accomplished a number of additional contributions, which concern (i) a note on thebound constraints handling for the CEC'05 benchmark set, (ii) computational results for an automatically tuned IPOP-CMA-ES on the CEC'05 benchmark set and(iii) a study of artificial bee colonies for continuous optimization. These additionalcontributions are to be found in the appendix to this thesis.

A joint antenna and user selection scheme for multiuser MIMO system

In this paper, we present a low-complexity algorithm for real-time joint user scheduling and receive antenna selection (JUSRAS) in multiuser MIMO systems. The computational complexity of exhaustive search for JUSRAS problem grows exponentially with the number of users and receives antennas. We apply binary particle swarm optimization (BPSO) to the joint user scheduling and receive antenna selection problem. In addition to applying the conventional BPSO to JUSRAS, we also present a specific improvement to this population-based heuristic algorithm; namely, we feed cyclically shifted initial population, so that the number of iterations until reaching an acceptable solution is reduced. The proposed BPSO for JUSRAS problem has a low computational complexity, and its effectiveness is verified through simulation results.

Swarm Intelligence for Sensor Selection Problems

In this paper, we apply the binary particle swarm optimization to the problem of selecting sensors from a set of sensors for the purpose of minimizing the error in parameter estimation. The motivation of selecting sensors rather than utilizing all sensors includes computational efficiency of parameter estimation and also the efficiency of energy consumption of sensor operations. The computational complexity of finding an optimal subset through exhaustive search can grow exponentially with the number ( and ) of sensors. If and are large, then it is not practical to solve this problem by evaluating all possible subsets of sensors. In addition to applying the general binary particle swarm optimization (BPSO) to the sensor selection problem, we also present a specific improvement to this population-based heuristic algorithm, namely, we use cyclical shifts to construct the members of the initial population, with the intention of reducing the average convergence time (the number of iterations until reaching an acceptable solution). The proposed BPSO for the sensor selection problem is computationally efficient, and its performance is verified through simulation results.

Low-complexity joint transmit and receive antenna selection for MIMO systems

In this paper, we present a low-complexity algorithm for real-time joint transmit and receive antenna selection in MIMO systems. The computational complexity of exhaustive search in this problem grows exponentially with the number of transmit and receive antennas. We apply Binary Particle Swarm Optimization (BPSO) to the joint transmit and receive antenna selection problem. In addition, applying the general BPSO to joint antenna selection, we also present a specific improvement to this population-based heuristic algorithm, namely, we feed cyclically shifted initial population so that the average convergence time (the number of iterations until reaching an acceptable solution) is reduced. The proposed BPSO for joint antenna selection problem has a low computational complexity, and its effectiveness is verified through simulation results.

Swarm intelligence-based strategic bidding in competitive electricity markets

In the competitive electricity markets, formation of supply bid is one of the main concerns, where suppliers have to maximise their profit under incomplete information of other competing generators. An environment is described in which suppliers bid strategically to sell electricity in a pool market. The bidding decision is optimised from a single supplier's viewpoint in both block-bid and linear-bid models of an electricity market. To include uncertain behaviour of other competing suppliers, two different probabilistic models are used. Their bids are constructed using probability distribution functions obtained from the decision-maker's observations of historical market data. Single supplier's decision-making problem is solved by a modern population-based heuristic algorithm, known as particle swarm optimisation (PSO). Search procedure of PSO is based on the concept of combined effect of cognitive and social learning of the members in a group. The effectiveness of the proposed method is tested with examples and the results are compared with the solutions obtained using the genetic algorithm approach.

Acoustic Radiation Optimization Using the Particle Swarm Optimization Algorithm

The present paper describes a fundamental study on structural bending design to reduce noise using a new evolutionary population-based heuristic algorithm called the particle swarm optimization algorithm (PSOA). The particle swarm optimization algorithm is a parallel evolutionary computation technique proposed by Kennedy and Eberhart in 1995. This algorithm is based on the social behavior models for bird flocking, fish schooling and other models investigated by zoologists. Optimal structural design problems to reduce noise are highly nonlinear, so that most conventional methods are difficult to apply. The present paper investigates the applicability of PSOA to such problems. Optimal bending design of a vibrating plate using PSOA is performed in order to minimize noise radiation. PSOA can be effectively applied to such nonlinear acoustic radiation optimization.