Why does MATLAB dot product function interpret r as 2 different variables. I want to use trigonometric identities. How can I fix it?

syms x y z u v r a

x=(a+r.*cos(u)).*cos(v);
y=(a+r.*cos(u)).*sin(v);
z=r.*sin(u);

X=[x y z]

X = 

Xu=diff(X,u)

Xu = 

Xv=diff(X,v)

Xv = 

E=dot(Xu,Xu)

E = 

simplify(E)

ans = 

Answer 1

[Steven Lord]

If you want MATLAB to assume that r is real, tell it that.

syms r1 % r1 could be complex
syms r2 real % r2 must be real
x1 = dot(r1, r1)

x1 = 

x2 = dot(r2, r2)

x2 = 

[Joan Miquel Pons Crespi]

Thank you. I had tried:

assume(r,'real')

but it did not work.