Matlab fmincon始终为零

Question

我有一个函数f（x）， 当我使用fmincon时，我收到了这个：

Initial point is a local minimum that satisfies the constraints.

Optimization completed because at the initial point, the objective function is non-decreasing 
in feasible directions to within the selected value of the optimality tolerance, and 
constraints are satisfied to within the default value of the constraint tolerance.

<stopping criteria details>

                                            First-order      Norm of
 Iter F-count            f(x)  Feasibility   optimality         step
    0       4    0.000000e+00    0.000e+00    0.000e+00

第一步。答案总是x0，但如果我找到f（x0），它就不等于零！可能是什么问题？