SEI

The Symplectic Epicycle Integrator (SEI), is a mixed variable second order symplectic integrator for the shearing sheet. Its main purpose is to simulate planetary rings in a local corotating frame. See Rein & Tremaine (2011) for details. The (vertical) epicyclic frequency OMEGA (OMEGAZ) needs to be set in the simulation. In previous versions of REBOUND, these variable were defined in the integrator, not the simulation.