The gravitational search algorithm (GSA) is a population-based heuristic optimization technique and has been proposed for solving continuous optimization problems. The GSA tries to obtain optimum or near optimum solution for the optimization problems by using interaction in all agents or masses in the population. This paper proposes and analyzes fitness-based proportional (rou- lette-wheel), tournament, rank-based and random selection mechanisms for choosing agents which they act masses in the GSA. The proposed methods are applied to solve 23 numerical benchmark functions, and obtained results are compared with the basic GSA algorithm. Experimental results show that the proposed methods are better than the basic GSA in terms of solution quality.
 Kennedy, J. and Eberhart, R.C. (1995) Particle Swarm Optimization. Proceedings of International Conference on Neural Networks, 4, 1942-1948. http://dx.doi.org/10.1109/ICNN.1995.488968
 Pham, D.T., Ghanbarzadeh, A., Koc, E., Otri, S., Rahim, S. and Zaidi, M. (2006) The Bees Algorithm: A Novel Tool for Complex Optimisation Problems. Proceedings of Intelligent Production Machines and Systems (IPROMS) Conference, 454-459.
 Karaboga, D. and Basturk, B. (2007) A Powerful and Efficient Algorithm for Numerical Function Optimization: Artificial Bee Colony (ABC) Algorithm. Journal of Global Optimization, 39, 459-171. http://dx.doi.org/10.1007/s10898-007-9149-x
 Geem, Z.W., Kim, J.H. and Loganathan, G.V. (2001) A New Heuristic Optimization Algorithm: Harmony Search. Simulation, 76, 60-68. http://dx.doi.org/10.1177/003754970107600201
 Rashedi, E., Nezamabadi-Pour, H. and Saryazdi, S. (2009) GSA: A Gravitational Search Algorithm. Information Sciences, 179, 2232-2248. http://dx.doi.org/10.1016/j.ins.2009.03.004
 Han, X. and Chang, X. (2012) A Chaotic Digital Secure Communica-tion Based on a Modified Gravitational Search Algorithm Filter. Information Sciences, 208, 14-27. http://dx.doi.org/10.1016/j.ins.2012.04.039
 Khajehzadeh, M., Taha, M.R., El-Sha?e, A. and Eslami, M. (2012) A Modi?ed Gravitational Search Algorithm for Slope Stability Analysis. Engineering Applications of Artificial Intelligence, 25, 1589-1597.