Conclusions and Future Research Directions

Recent research advances have been made in different types of hyper-heuristics (HH), namely selection HH and generation HH, employing both constructive and perturbative low-level heuristics (llh). Among the four types of HH, selection HH (Chapters 2, 3) received more research attention than generation HH (Chapters 4, 5). This may be due to the research challenges in developing genetic programming and grammatical evolution, which are the main high-level techniques used in generation HH. These include the issue of bloating, which leads to the problem of readability and interpretability [14]. Among most of the generation HH, the newly generated llh have thus rarely been reused on new instances or problems. This presents challenges but interesting research directions for further investigations.