  Energy (or Lyapunov) functions are used to prove stability of equilibria, or
to indicate a gradient-like structure of a dynamical system. Matano constructed
a Lyapunov function for quasilinear non-degenerate parabolic equations. We
modify Matano's method to construct an energy formula for fully nonlinear
degenerate parabolic equations. We provide several examples of formulae, and in
particular, a new energy candidate for the porous medium equation.
