ソリトン
∂ ∂ x ( ∂ u ∂ t + 6 u ∂ u ∂ x + ∂ 3 u ∂ x 3 ) ± ∂ 2 u ∂ y 2 = 0 {\displaystyle {\frac {\partial }{\partial x}}\left({\frac {\partial u}{\partial t}}+6u{\frac {\partial u}{\partial x}}+{\frac {\partial ^{3}u}{\partial x^{3}}}\right)\pm {\frac {\partial ^{2}u}{\partial y^{2}}}=0}