Controllability for two-Kuznetsov-Ma solitons in a (2 + 1)-dimensional graded-index grating waveguide Hai-Ping Zhu, Zhen-Huan Pan and Jian-Ping Fang Eur. Phys. J. D, 68 3 (2014) 69 Published online: 27 March 2014 DOI: 10.1140/epjd/e2014-40681-x