Routhian

In the branch of physics known as dynamics the Routhian is a hybrid of the Lagrangian and the Hamiltonian for a system. The Hamiltonian can be obtained by a Legendre transform of the Lagrangian; if this transformation is performed only with regards to cyclic coordinates (those not appearing explicitly in the Lagrangian), the result is called the Routhian.

It is named after Edward John Routh ( 1831 to 1907)