TOP > Research > Department of Systems and Social Informatics > Department of Complex Systems Science > Many-body Systems Science Group > TOKITA Keiichiro

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Department of Complex Systems Science

TOKITA Keiichiro
Many-body Systems Science Group
Dr. of Science
Research Field
Statistical Physics / Mathematical Biology / Science of Diversity
TOKITA Keiichiro

Current Research

How can we understand and control the complex systems with diverse elements and complex interactions among them?

Kei Tokita studies various interdisciplinary subjects, e.g., physical, biological and social systems in the light of statistical mechanics, nonlinear dynamics and computational physics. KT is interested in a wide range of topics including critical phenomena, phase transitions, biomoleculars, neural networks, ecological systems, virus evolution and immune response, game theory, language evolution, economic systems, social systems, etc. Although these subjects appear quite different from each other at first glance, they share a key concept: complexity of interactions. Complex behaviors of these systems emerged from various interactions between diverse elements, e.g. amino acids, neurons, species, viruses and immune cells, etc. Studying them from the point of statistical mechanics, we can make each particular case more clear. We also focus on on new methodologies of scientific computing such as a new Monte Carlo method based on extended ensembles implemented on a supercomputer and a PC&GPU cluster system with more than 100CPUs. A free atmosphere is another feature of our laboratory and we have hosted international students from Bulgaria, Indonesia and Korea.



  • 1989 B.Eng., Department of Applied Physics, Faculty of Science and Engineering, Waseda University.
  • 1991 M.Sci., Department of Physics and Applied Physics, Graduate School of Science and Engineering, Waseda University.
  • 1994, Department of Pure and Applied Sciences, Graduate School of Science, University of Tokyo.
  • 1994-2000, Assistant Professor, Department of Physics, Osaka University.
  • 1996-1998, Visiting scholar, Harvard University.
  • 2000-2007, Associate Professor, Cybermedia Center and Graduate School of Science, Osaka University.
  • 2002-2007, Associate Professor, Graduate School of Frontier Biosciences, Osaka University.
  • 2003-2004, Visiting scholar, Harvard University
  • 2007-2013, Associate Professor, Cybermedia Center, Graduate School of Science and Graduate School of Frontier Biosciences, Osaka University.
  • 2013-Current, Professor, Graduate School of Information Science, Nagoya University.

Academic Societies

  • The Physical Society of Japan
  • The Japanese Society for Mathematical Biology
  • The Ecological Society of Japan


  1. "Understanding Biological Networks (Japanese)" (Kyoto University Press)
  2. "Structure and Prediction in Complex Systems (Japanese)" (Kyoritsu Shuppan)
  3. "Complexity (Japanese translation of the original book by R. Badii and A. Politi)"(Sangyo Tosho)
  4. Haruyuki Irie and Kei Tokita, "Species-area relationship for power-law species abundance distribution", International Journal of Biomathematics 5 (2012) 1260024 (9 pages).
  5. Yoshimi Yoshino, Tobias Galla and Kei Tokita, "Rank abundance relations in evolutionary dynamics of random replicators", Physical Review E 78 (2008) 031924 (11 pages).
  6. Yoshimi Yoshino, Tobias Galla and Kei Tokita, "Statistical mechanics and stability of a model eco-system", Journal of Statistical Mechanics (2007) P09003 (24 pages).
  7. Kei Tokita, "Statistical mechanics of relative species abundance", Ecological Informatics 1 (2006) 315-324.
  8. Kei Tokita, "Species abundance patterns in complex evolutionary dynamics", Physical Review Letters 93 (2004) 178102 (4 pages).
  9. Kei Tokita and Ayumu Yastuomi, "Emergence of a complex and stable network in a model ecosystem with extinction and mutation", Theoretical Population Biology 63 (2003) 131-146.