Finding global minimum with rand

I'm supposed to use the MATLAB function "rand" to generate a large number of random vectors in 3-space, with coordinates between −6 and 6. Then I have to evaluate f at those points to find the minimum. But I don't know if I'm doing it correctly. My function is f(x, y,z) = x^4 + y^4 + z^4 − 3*x^2 − 8*y^2 − 6*x*z − 4*x*y − 10*z^2 + 6*y. Here's what I have so far:

Answer 1

[Torsten]

fumin = Inf;
for i = 1:100000
  u = -6 + 12*rand(3,1);
  fu = f(u);
  if fu < fumin
    umin = u;
    fumin = fu;  
  end
end

[Ikenna Iwudike]

I'm getting these errors when I use that code:

Array indices must be positive integers or logical values.

Error in sym/subsref (line 909)

R_tilde = builtin('subsref',L_tilde,Idx);

[Torsten]

This error message cannot stem from my code above.

At least if f is defined as you showed us:

f = @(u) u(1)^4 ... etc.

[Ikenna Iwudike]

Oh ok, I didn't add that in. Thanks.