Nonlinear parity-time symmetric closed-form optical quadrimer waveguides: attractor perspective Samit Kumar Gupta, Jyoti P. Deka and Amarendra K. Sarma Eur. Phys. J. D, 69 8 (2015) 199 Published online: 18 August 2015 DOI: 10.1140/epjd/e2015-60034-7