Tsing, N.K.Different norms are considered to replace the Euclidean norm in an algorithm given by Fan and Tits (IEEE Trans. Automat. Contr., AC-33, pp. 284-289, 1988) which is used for the computation of the structured singular value of any matrix. It is shown that the l_{1-norm} is the best possible norm in a certain sense.en-USTechnical Report