# Pharos Library

### Site Tools

lagrangian_formalism

# Lagrangian formalism

Least action principle

The Lagrangian formalism is a universal approach to describe the evolution of a physical system. The basic idea is the least action principle, the idea that the evolution minimizes some quantity (for example the energy).

The resulting equations are called the Euler-Lagrange equations. This formalism can be applied to all known physical theories, such as classical mechanics, general relativity or quantum field theory.

## Material

A nice explanation in three steps (intuitive, example, abstract) can be found here:

• Hamiltonian formalism
• Euler-Lagrange equation