Some questions about vector

*To*: mathgroup at smc.vnet.net*Subject*: [mg74543] Some questions about vector*From*: "Qi Zhang" <qzhang81 at gmail.com>*Date*: Sun, 25 Mar 2007 01:26:48 -0500 (EST)

input: Clear[f]; f[v] = Sum[(i*v[i]), {i, 1, N}] D[f[v], v[i]] the output is \!\(1\/2\ N\ \((1 + N)\)\) However what I expect is i What should I do in order to get the the answer I expected? Thanks a lot. -- Best, Qi Zhang