Question for directional derivative.

How to solve the following question in matlab?

u(x1,x2) = x1^2 - x2^2. Calculate the derivative of u in the direction n = (8,-8) at the point (1,1).

Answer 1

[KSSV]

u = @(x1,x2) x1^2-x2^2 ; 
% derivatives at point (1, 1) 
x1 = 1 ; x2 = 1 ; 
% derivatives 
dudx1 = 2*x1 ;
dudx2 = -2*x2 ;

dudx = [dudx1 dudx2] ; 
% directional derivative along (8,-8)
v = [8 -8] ;
uv = v/norm(v) ;
iwant = dudx.*uv

For theory refer: https://mathinsight.org/directional_derivative_gradient_examples