Nonlinear parity-time symmetric closed-form optical quadrimer waveguides: attractor perspectiveSamit Kumar Gupta, Jyoti P. Deka and Amarendra K. SarmaEur. Phys. J. D, 69 8 (2015) 199DOI: https://doi.org/10.1140/epjd/e2015-60034-7