Problem with minimizing a convex function

Hello dear people,

I want to minimize a convex function.

The minimum is at x=50 with its value y=10.

Currently I am at x=30 and got following function:

material=@(x)parabola(30+x*0.00005);

with:

lb=0;

ub=5000;

x0=0;

[x,fval]=fmincon(material,x0,A,b,Aeq,beq,lb,ub,nonlcon);

Now the result for x should be 5000 to get an index of 30.25 but matlab gives out 0 for 0 instead of 5000.

Why is that the case?

Regards!