The Kaup–Kupershmidt equation (named after David J. Kaup and Boris Abram Kupershmidt) is the nonlinear fifth-order partial differential equation
It is the first equation in a hierarchy of integrable equations with Lax operator
It has properties similar (but not identical) to those of the better-known KdV hierarchy in which the Lax operator has order 2.
References
Kaup–Kupershmidt equation Wikipedia(Text) CC BY-SA