Nature-inspired optimization algorithms especially those based on the hunting behaviors of the creatures assume that the hunting operations are performed in a safe environment. However, generally, there are threats in real-life for the hunter-animals. This paper focuses on these threat factors and proposes that they can be used to improve the searching abilities of the algorithms. Gray wolf optimization (GWO) algorithm was selected to present the proposed approach and it was assumed that there was a mountain lion as the threat factor living in the same habitat with the wolf pack. The relations between the two predators were modeled and used to improve the performance of the algorithm. Five experiments were conducted to test the performance of the proposed method and the results were compared with the GWO and four optimization algorithms from the literature. It is shown that the proposed algorithm obtained best results for 21 of the 50 benchmark functions, while its closest competitor achieved the best results for 16 functions. Besides, the results of the Wilcoxon signed-rank test indicated that the proposed method is superior to all other methods. In addition, it was shown that the threat factor approach does not cause a significant increase in the processing time.
K E Y W O R D SGWO algorithm, nature-inspired optimization, threat factor approach
INTRODUCTIONNature is a great source for modeling optimization algorithms since there are so many creatures, events, or any other phenomena that can be used as the base for these algorithms. Therefore, nature-inspired optimization algorithms have been very popular over the past three decades.Generally, these algorithms can be divided into four classes as evolutionary-based, swarm-based, physics-based, and human-based algorithms. 1Evolutionary-based algorithms model natural evolution concepts such as mutation and natural selection. These algorithms are based on the rule of eliminating weak entities while providing that the strong individuals pass to the next generation. Genetic algorithm 2 which was proposed by Holland is the best-known evolutionary algorithm. differential evolution (DE), 3 genetic programming, 4 learner performance based behavior 5 algorithm, and biogeography-based optimizer 6 are some of the other algorithms based on the evolutionary approach. Swarm-based optimization algorithms are derived from the behaviors of the herds of the creatures to reach the food. Particle swarm optimization (PSO) is the most-known swarm-based optimization algorithm. PSO, simply, mimics the searching-food behaviors of a swarm of fish or birds. 7 Ant colony optimization, 8 artificial bee colony, 9gray wolf optimization (GWO), 10 ant lion optimization (ALO), 11 whale optimization algorithm (WOA), 12 dragonfly algorithm. 13 Moth-flame optimization (MFO), 14 salp swarm algorithm, 15 fish-swarm algorithm, 16 bird mating optimizer, 17 bat-inspired algorithm, 18 firefly algorithm, 19 naked mole-rat algorithm, 20 cuckoo search algorithm, 21 donkey and smuggler optimization, 22 and fit...