Recursion operators for a class of integrable third-order evolution equations

Abstract

We consider $u_t=u^α u_{xxx}+n(u)u_xu_{xx}+m(u)u_x^3+ r(u)u_{xx} +p(u)u_x^2 + q(u)u_x+s(u)$ with $α=0$ and $α=3$, for those functional forms of $m, n, p, q, r, s$ for which the equation is integrable in the sense of an infinite number of Lie-Bäcklund symmetries. Local $x$- and $t$-independent recursion operators that generate these infinite sets of symmetries are obtained for the equations. A combination of potential forms, hodograph transformations and $x$-generalised hodograph transformations are applied to the obtained equations.