To reproduce the error, run:
f1 = @(x,y,z) 8*x.^3+36*y.^3+z.^2-36;
f2 = @(x,y,z) 4*x.^2-y.^2-21*z;
f3 = @(x,y,z) 4*x.^2-2*y.^2+10*z.^2;
xxx = linspace(-3,3);
yyy = linspace (-3,3);
a = sym(f1);
b= sym(f2);
c= sym(f3);
s = subs(a,'z',1);
t = subs(b,'z',1);
u = subs(c,'z',1);
[x,y] = meshgrid(xxx,yyy);
mesh(x,y,s);
hold on mesh(x,y,t);
hold on mesh(x,y,u);
When you give mesh(x,y,s), s is just a symbolic function. I'm guessing you need to say:
[x,y] = meshgrid(xxx,yyy);
s = subs(s,'y',y);
s = subs(s,'x',x);
mesh(x,y,s)
but it's taking a while to run so I can't confirm if this is correct. It feels like this produces an s that is far too large.
