subscript question

*To*: mathgroup at smc.vnet.net*Subject*: [mg71831] subscript question*From*: "dimitris" <dimmechan at yahoo.com>*Date*: Thu, 30 Nov 2006 06:05:39 -0500 (EST)

mat = Table[Subscript[x, i, j], {i, 1, 3}, {j, 1, 3}]; Something like Apply[Plus, mat, 1] works fine. However Tr[mat] returns back the command. Why? Thanks Dimitris