A note on SOR() splitting of an -matrix

Recently, Wang and Huang (J. Comput. Appl. Math. 135 (2001) 325, Corollary 4.7) assumed that SOR( ω ) splitting with ω ⩾ 1 is a weak regular splitting of an M -matrix. In this note, we point out that SOR( ω ) splitting with ω > 1 can never be a weak regular splitting of an M -matrix. This shows that Changʹs counterexample (J. Comput. Appl. Math. 167 (2004) 251, Example 1) is not an appropriate one since the SOR( ω ) splitting with ω > 1 given there is not a weak regular splitting.