  We combine the recent relaxation approach with multiderivative Runge-Kutta
methods to preserve conservation or dissipation of entropy functionals for
ordinary and partial differential equations. Relaxation methods are minor
modifications of explicit and implicit schemes, requiring only the solution of
a single scalar equation per time step in addition to the baseline scheme. We
demonstrate the robustness of the resulting methods for a range of test
problems including the 3D compressible Euler equations. In particular, we point
out improved error growth rates for certain entropy-conservative problems
including nonlinear dispersive wave equations.
