# Derivative operator

Dear FreeFem users,

suppose u is a “fespace” function defined on a two dimensional mesh,
how does the operator dx(u) approximate u?

Mordechai.

I suggest you to read the documentation here

Thanks Julien,
I looked in the documentation but didn’t see any references on the dx operator.

I would like to to use a second order approximation in order to approximate the space derivatives (in x and y directions) however I don’t know if the dx operator does it already.
And if not how can I approximate the space derivative using for example the central difference scheme (u_i+1-u_i-1/2h) h is length in space.