The robustness against inclusion of new elements is an essential feature of diverse kinds of real complex systems such as living organisms, ecosystems, social and economic systems, and complex engineering system with bottom-up design principle. By proposing a simple model, we have revealed a general mechanism of determining the robustness of such systems against inclusion of elements with totally random interactions. We are elaborating this approach by comparing the results with real systems and extending the model.
Simulational study of various collective phenomena in non-equilibrium systems is of also my interest. The topic includes: the collective motions of self-propelled particles (e.g. pedestrians and group of animals), group chase and escape, foraging process, maintenance of cooperation via indirect reciprocity, market-market competition, traffic flow, etc.
Data analysis of the dynamics of real complex systems is another important component of our study. This includes developing new methods for each problem, such as the correlation in stock market and the cell distribution in the fruitfly brain.