Comment on "Least squares low-pass filters with nonmonotonic response

In the above \footnote[1]{paper} a class of all-pole low-pass filters has been derived using the least mean squares approximation technique and three subclasses have been obtained by imposing different constraints on the coefficients of the characteristic function. It is shown that these functions have previously been derived in explicit form by minimizing the ratio of the reflected power to the transmitted power in terms of a weighed least mean squares norm. [1] H. S. Malvar and L. P. Calôba, IEEE Trans. Circuits Syst., vol. CAS-27, pp. 1270-1272, Dec. 1980.