“…Bernard Koopman introduced the Koopman operator in [7] and this seminal work became a popular tool with [1] and several other works followed where Koopman operator theory is used in the system identification [3,8], for control design [9,10,11], sensor fusion [12] and analysis of spectrally conjugate systems [13], finding observability gramians or observers [14,15,16], study of chaotic systems [17,18], data-driven information transfer [19,20,21], data-driven based causal inference in dynamical systems [22], in data-driven classification of power system stability [23], and in power system coherency identification, power system stability monitoring [24,25,26,25,27], dynamic state estimation in power networks [28], fault, cyber-attack localization in cyber-physical systems [29,30], computational neuroscience applications [31] and data assimilation for climate forecasting [32].…”