For dimension 4 the number of symbols is 64, and using symmetry this number is only reduced to 40. Certainly there are many calculations and this is just to find the equations of geodesics (after, we must solve or analyze it).

We will see in this section, the Lagrangian method allows us to obtain the geodesic equations and hence obtain the Chistoffel symbols. in a simpler way.

Ideas are the basis of the calculus of variations called principle of least action of Euler-Lagrange

First of all, a notation matter: from now on we will use the dot character "." to denote the derivate, this is a notation very used in physics, for example to denote we will use .

### Principle of least action from Euler-Lagrange

Let and let C be the set of functions such us

y(a)=c, e y(b)=d if

reaches its minimum at some then, is a solution of differential equation