Yong Chen Zhenya Yan Weierstrass semi-rational expansion method and new doubly periodic solutions of the generalized Hirota-Satsuma coupled KdV system. 85-91 2006 177 Applied Mathematics and Computation 1 http://dx.doi.org/10.1016/j.amc.2005.10.037 db/journals/amc/amc177.html#ChenY06