A question about derivatives of quadratic products

*To*: mathgroup at smc.vnet.net*Subject*: [mg49080] A question about derivatives of quadratic products*From*: yangjq at soton.ac.uk (afh)*Date*: Wed, 30 Jun 2004 05:34:25 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Hello, I am a new user of mathematica. I met a question about derivatives as following: D = Norm[w, 2]^2/2+sum(αi(yi(w.x+b+sqrt(w.M.w))-1)) (which i=1 to n) w and x are two-dimension vectors, yi is a number either -1 or 1, b is a number, M is a 2*2 matrix, αi is a lagrange coefficient. I want to get the value of w when D's derivative on w is equal to zero. But many errors happen, and it seems mathematica does not know what it should do next. Can somebody help me? Many thanks for your kind help.