Gradient of Substituted Symbolic Variables

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bh1910
bh1910 2015-7-25
编辑： Walter Roberson 2015-7-25
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

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bio lim
bio lim 2015-7-25
编辑：bio lim 2015-7-25
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

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