在MATLAB信號處理工具箱中，給出了一個(gè)辨識系統(tǒng)傳遞函數(shù)模型的函數(shù)invfreqs（），該函數(shù)的調(diào)用格式是

　?。跙，A］=invfreqs（H，W，n，m）

　　其中W為由離散頻率點(diǎn)構(gòu)成的向量，n和m為待辨識系統(tǒng)的分子和分母階次，H為為復(fù)數(shù)向量，其實(shí)部和虛部為辨識時(shí)用到的實(shí)部和虛部。返回的B和A分別為辨識出的傳遞函數(shù)的分子和分母的系數(shù)向量。

　　通過A和B可得到傳遞函數(shù)

　　函數(shù)invfreqs（）的Matlab解釋：

　　》》 help invfreqs

　　INVFREQS Analog filter least squares fit to frequency response data.

　　［B，A］ = INVFREQS（H，W，nb，na） gives real numerator and denominator coefficients B and A of orders nb and na respectively， where H is the desired complex frequency response of the system at frequency points W， and W contains the frequency values in radians/s.

　　INVFREQS yields a filter with real coefficients. This means that it is sufficient to specify positive frequencies only; the filter fits the data conj（H） at -W， ensuring the proper frequency domain symmetry for a real filter.