fmincon: how should x0 be specified

I want to minimize a multivariable uncontstrained function with lower and upper bounds. I don't have any information or idea how to define x0 as initial values and cannot accept zero values.Here is the code

obj = @(x) (1-x(1))*(5*x(2)^3+x(2)^2) + x(1)*(0.2*x(2)^3+1.2*x(2)^2);
x0=ones(0,30);
[x,fval] = fmincon(obj,x0,[],[],[],[],[0;30],[1;50])

How should the x0 be specified regarding the bounds of the variables?

Answer 1

[Star Strider]

The way you specified ‘x0’, it is a ‘0×30 empty double matrix’!

I would specify it as the median of the bounds, so here:

lb = [0;30];
ub = [1;50];
x0 = median([lb ub],2);

producing:

x0 =
    0.5000
   40.0000

[Thalassia Nouni]

Thank you for the answer, it runs now. Can anyone specify how is x0 determined? In the documentation it writes that it is the initial values of x, but what if it is 0?

[Torsten]

x0 is a value that you arbitrarily set. So you can decide whether it is 0 or not. Usually, a value is chosen that you think is senseful and close to the solution.

[Star Strider]

@Torsten — Thank you.