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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.