Schnabel, J., H. Cartarius, J. Main, G. Wunner, and W. D. Heiss. “SIMPLE MODELS OF THREE COUPLED PT -SYMMETRIC WAVE GUIDES ALLOWING FOR THIRD-ORDER EXCEPTIONAL POINTS”. Acta Polytechnica, vol. 57, no. 6, Dec. 2017, pp. 454-61, doi:10.14311/AP.2017.57.0454.