[ returns the h,w] = freqz(b,a,n)n-point frequency response vector h and the corresponding angular frequency vector w for the digital filter with transfer function coefficients stored in b and a.
invfreqz is the inverse operation of freqz; it finds a discrete-time transfer function that corresponds to a given complex frequency response. From a laboratory analysis standpoint, invfreqz can be used to convert magnitude and phase data into transfer functions.
[b,a] = invfreqz(h,w,n,m) returns the real numerator and denominator coefficients in vectors b and a of the transfer function
whose complex frequency response is given in vector h at the frequency points specified in vector w. Scalars n and m specify the desired orders of the numerator and denominator polynomials.
Frequency is specified in radians between 0 and π, and the length of h must be the same as the length of w. invfreqz uses conj(h) at -w to ensure the proper frequency domain symmetry for a real filter.
原文：https://www.cnblogs.com/blog-of-cm/p/11734451.html