Comments on "A derivation of the normal equation in FIR Wiener filters

A shortcut is pointed out to derive the normal equation for complex variables. In the paper by Y.-D. Huang and C.-T. Chen (see IEEE Trans. Acoust. Speech Signal Process., vol.37, no.5, p.759-60, 1989), certain difficulties are addressed that arise in the derivation of the normal equation for complex variables. The authors of that paper solve this problem by using gradient methods. However, there is a shortcut to solving problems of this type that is extremely simple to apply, with a well-established theoretical basis. For the problem in the above paper, this procedure results immediately in the normal equation. This method has wider applications.<>