在程序运行结果中，出现这样的提示:(请大家帮我分析一下到底是哪里出了问题，多谢！)
Solver stopped prematurely.
fminunc stopped because it exceeded the function evaluation limit,
options.MaxFunEvals = 300 (the default value).
Computing finite-difference Hessian using user-supplied objective function.
Problem appears unbounded.
fminunc stopped because the objective function value is less than
or equal to the default value of the objective function limit.
<stopping criteria details>
Solver stopped prematurely.
fminunc stopped because it exceeded the function evaluation limit,
options.MaxFunEvals = 300 (the default value).
Computing finite-difference Hessian using user-supplied objective function.
fminunc stopped because the objective function value, -Inf, is less than
or equal to options.ObjectiveLimit = -1.000000e+20.
Optimization Metric                                         Options
objective value =       -Inf               ObjectiveLimit =  -1e+20 (default)