Generally speaking, the situation of multivariable is much more complicated than that of single input variable. There are not only different unknown dynamic characteristics and static relationships between tuning variables and objective function, but also there may exist unknown dynamic and static relationships between these tuning variables. When the system works, the noise pulsation of the tuning variables is also very complex, which cannot be guaranteed to be independent of each other, and of course, they are generally impossible to be white noise.