On Relationship of Koopman Eigenvalues and Frequencies in Dynamic Mode   Decomposition
  The frequency estimation from the Koopman eigenvalues (phase angles) obtained via Dynamic Mode Decomposition (DMD) is addressed. Since the calculations of the frequencies from the phase angles are nonunique, the modifications of DMD for uniqueness restoration are considered. The nonlinear oscillating mode of supersonic jet, impinging the flat plate, is used as a toy problem. 
Aleksey Alekseev
physics.flu-dyn