The Modified IWO Algorithm for Optimization of Numerical Functions Daniel Kostrzewa and Henryk Josi´ nski Silesian University of Technology, Akademicka 16 PL-44-100 Gliwice, Poland {Daniel.Kostrzewa,Henryk.Josinski}@polsl.pl Abstract. The Invasive Weed Optimization algorithm (IWO) is an op- timization method inspired by dynamic growth of weeds colony. The au- thors of the present paper have modified the IWO algorithm introducing a hybrid strategy of the search space exploration. The goal of the project was to evaluate the modified version by testing its usefulness for numer- ical functions minimization. The optimized multidimensional functions: Griewank, Rastrigin, and Rosenbrock are frequently used as benchmarks which allows to compare the experimental results with outcomes reported in the literature. Both the results produced by the original version of the IWO algorithm and the Adaptive Particle Swarm Optimization (APSO) method served as the reference points. Keywords: Invasive Weed Optimization algorithm, Griewank function, Rastrigin fuction, Rosenbrock function. 1 Introduction The Invasive Weed Optimization (IWO) algorithm is an optimization method, in which the exploration strategy of the search space (similarly to the evolutionary algorithm) is based on the transformation of a complete solution into another one. Its idea was inspired by observation of dynamic spreading of weeds and their quick adaptation to environmental conditions [1]. The authors of the method from University of Tehran emphasized its useful- ness for continuous optimization tasks. Their research was focused inter alia on minimization of the multimodal functions and tuning of a second order com- pensator [1], antenna configurations [2], electricity market dynamics [3], and a recommender system [4]. The authors of the present paper have modified the IWO algorithm intro- ducing a hybrid strategy of the search space exploration (described in detail in section 2) and broadened the scope of the IWO algorithm application dealing skillfully with an important discrete optimization task from the databases area – the join ordering problem – for both – centralized and distributed data [5]-[6]. The symmetric TSP was also successfully solved by the modified IWO equipped with the inver-over operator [7]. The goal of the present paper is an evaluation of the modified IWO based on the effects of the optimization of the Griewank, Rastrigin and Rosenbrock L. Rutkowski et al. (Eds.): SIDE 2012 and EC 2012, LNCS 7269, pp. 267–274, 2012. c  Springer-Verlag Berlin Heidelberg 2012