Gradient of Substituted Symbolic Variables

Hello, I'm having a problem with finding the gradient of a substituted symbolic variable:

My code is:

syms x y z

f = x^2 + x + y^2 - y;

subs(f, y, z)

g = gradient(f, [x, z])

When I run it, the gradient turns out to be [2*x+1, 0]. It doesn't seem to calculate the z variable derivative. Does anyone know why?

Tks

Answer 1

[bio lim]

It is because your function f is not updated. Here is what you need to do.

syms x y z

 f = x^2 + x + y^2 - y;
 f = subs(f,y,z);
 g = gradient(f, [x,z])

The result is

 g =

 2*x + 1
 2*z - 1

[bh1910]

Tks a lot.

[bio lim]

My pleasure.