Comparison of solution space exploration by NSGA2 and SPEA2 for Flexible Job Shop Problem

In this paper, we present a new metric to evaluate the meta-heuristics by studying their exploration of the solution space. We propose an efficient representation of the solution space by a one-dimensional map. To evaluate the exploration of space, relative and absolute metrics have been proposed. For the tests, we used the NSGA2 and SPEA2 on Flexible Job Shop Problem (FJSP) with the objectives to reduce the makespan (C_max) and to produce the jobs just in time (Σ^N_i=1 Z_i, with Z_i = T_i + E_i, T is the tardiness and E is the earliness). The results show that the NSGA2 explore more 6.78% solutions on average than SPEA2.