This note gives the correction to a few mistakes in the aforementioned paper. It is also found that the derived reduced model (fourthorder) is unstable.Index Terms-Discrete linear system, model reduction.A sixth-order Chebyshev Type-I filter, shown in (1) at the bottom of the page, is given in [1]. This filter is unstable (see Fig. 1). Therefore, the simulations results shown in [1, are irrelevant.The filter, shown in (2) at the bottom of the page, considered in [2] is stable (see Fig. 1). The reduced-order models of [2] are the same as in [1]. Thus, the filter shown in [1] appears to be the same as the one shown in [2].Therefore, it is evident that the equation showing sixth-order Chebyshev Type-I filter [1], contains a few typographical errors. The errors are as follows.i) The incorrect coefficient of z in the numerator. The correct coefficient of z is 0.06417. Fig. 1. Time response of original filters [1], [2]. ii) Missing coefficient of z in the denominator. The correct missing coefficient of z is 00.6859. iii) The incorrect coefficient of z 0 in the denominator. The correct coefficient of z 0 is 0.1962. Thus, the correct form of filter T (z) in [1] is as shown in (2). The reduced third-order [1], [2] and the fourth-order [1], [2] models are A rf = 0:6320 00:4430 0:0438 0:4430 0:2518 0:1919 00:0438 0:1919 0:6390 B rf = [0:5853 0 0:5870 0:0986] 3 C rf = [0:5853 0:5870 0 0:0986] G3(z) = C rf (e jw I 0 A rf ) 01 B rf = 00:0117z 2 + 0:4730z 0 0:3239 z 3 0 1:5228z 2 + 0:8852z 0 0:2117T (z) = 0:01069z 6 + 0:06417z 5 + 0:1604z 4 + 0:2139z 3 + 0:1604z 2 + 0:6417z + 0:01069 z 6 0 1:464z 5 + 2:291z 4 0 2:06z 3 + 1:464z 2 0 0:685 = 0:01069 + 0:0799z 5 + 0:1359z 4 + 0:2359z 3 + 0:1447z 2 + 0:6417z + 0:0180 z 6 0 1:464z 5 + 2:291z 4 0 2:06z 3 + 1:464z 2 0 0:685(1) T1(z) = 10 02 1:069z 6 + 6:417z 5 + 16:04z 4 + 21:39z 3 + 16:04z 2 + 6:417z + 1:069 z 6 0 1:464z 5 + 2:291z 4 0 2:06z 3 + 1:464z 2 0 0:6859z + 0:1962 = 0:01069 + 0:0799z 5 + 0:1359z 4 + 0:2359z 3 + 0:1447z 2 + 0:0715z + 0:0086 z 6 0 1:464z 5 + 2:291z 4 0 2:06z 3 + 1:464z 2 0 0:6859z + 0:1962(2) 1549-8328/$25.00
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