Kadomtsev-Petviashvili Equation
The partial differential equation 3/4 U_y + W_x = 0, where W_y + U_t - 1/4 U_(x x x) + 3/2 U U_x = 0 (Krichever and Novikov 1980; Novikov 1999). Zwillinger and Calogero and Degasperis give the equation as d/(dx)(u_t + u_(x x x) - 6u u_x) ± u_(y y) = 0.