text: Take the simple example of a barotropic, inviscid vorticity-free fluid.
  Then, the conjugate fields are the mass density field &rho; and the velocity potential &phi;. The Poisson bracket is given by
  and the Hamiltonian by:
  where e is the internal energy density, as a function of &rho;. 
  For this barotropic flow, the internal energy is related to the pressure p by:
  where an apostrophe (), denotes differentiation with respect to &rho;'.
  This Hamiltonian structure gives rise to the following two equations of motion:
  where  is the velocity and is vorticity-free. The second equation leads to the Euler equations:
  after exploiting the fact that the vorticity is zero:
  As fluid dynamics is described by non-canonical dynamics, which possess an infinite amount of Casimir invariants, an alternative formulation of Hamiltonian formulation of fluid dynamics can be introduced through the use of Nambu mechanics