David  Liu, Zhen, Bo , Ge, Li , Hernandez, Felipe , Pick, Adi , Burkhardt, Stephan , Liertzer, Matthias , Rotter, Stefan , and Johnson, Steven G. 2017. ?Symmetry, Stability, And Computation Of Degenerate Lasing Modes?. Physical Review A, 95, 2, Pp. 023835.