Euler-Lagrange equation

Etymology
Named after the Swiss mathematician and physicist (1707–1783), and the Italian-born French mathematician and astronomer  (1736–1813).

Noun

 * 1)  A differential equation which describes a function  which describes a stationary point of a functional,, which represents the action of , with L representing the Lagrangian. The said equation (found through the calculus of variations) is $${\partial L \over \partial \mathbf{q}} = {d \over dt} {\partial L \over \partial \mathbf{\dot q}}$$ and its solution for  represents the trajectory of a particle or object, and such trajectory should satisfy the principle of least action.