Erskine, Adam; Joyce, Thomas; Herrmann, J. Michael: 'The critical state in particle swarm optimisation' (Control, Robotics and Sensors, 2018), 'Swarm Intelligence - Volume 1: Principles, current algorithms and methods', Chap. 10, pp. 265-295, DOI: 10.1049/PBCE119F_ch10
IET Digital Library, https://digital-library.theiet.org/;jsessionid=16u4o27qhl3vz.x-iet-live-01content/books/10.1049/pbce119f_ch10