In the below expressions:
syms x1 x2 H f
xs = [1 1];
f = (12*x1^3 - 20*x1^3*x2^2 + 6*x2^2 + x1^2 +9);
H = hessian(f);
So the term H(1,1) would be a symbolic with a value (- 120*x1*x2^2 + 72*x1 + 2)
What is the simplest way to calculate the value of this expression at a point, say (x1,x2) = (1,2) ?