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From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Question on the derivate /calculus of a 2-norm matrix . Thanks a lot
Date: Mon, 26 Jul 2010 03:01:04 +0000 (UTC)
Organization: Anhui University
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"Matt J " <mattjacREMOVE@THISieee.spam> wrote in message <i2it4t$73b$1@fred.mathworks.com>...
> "Antony " <mutang.bing@gmail.com> wrote in message <i2irns$94i$1@fred.mathworks.com>...
>
> > I have another problem. Maybe we can not directly solve it and I think the result might be more complxe than my former problem. The problem is:
> >   if g(x) = ||KX-B||^0.6 with all the other settings as the former problem, what is \partial{g}/\partial{x}?
> ========
>
> This is equivalent to  (||KX-B||^2)^0.3
>
> So you can use your original result, with one more step of the chain rule leading to
>
> Gradient = 0.3*(||KX-B||^2)^(-.7)  * 2*K'*(K*X-B)

Why not write it as Gradient = 0.3 *2*K'*(K*X-B)*(||KX-B||^2)^(-.7) according to the chain rule? It is because K'*(K*X-B) is a scalar and there is no difference between them? Thank you!