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Subject: Re: Question on the derivate /calculus of a 2-norm matrix . Thanks a lot
Date: Mon, 26 Jul 2010 02:26:04 +0000 (UTC)
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"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <i2i2st$n4j$1@fred.mathworks.com>...
> "Antony " <mutang.bing@gmail.com> wrote in message <i2he90$21a$1@fred.mathworks.com>...
...
>  I*K'*K*X + I*K'*K*X = 2*K'*K*X.
> 
>   If you are not convinced by this last argument, you can always show it rigorously using summation notion.  It is just a problem in taking the derivatives of a homogeneous quadratic function of many variables.
> 
> Roger Stafford

Thank you, Roger. The explanation is extremely clearly and helpful, especially on how to rewrite the 2-norm into matrix multiplication and how the identity matrix is generated. I think I fully understand this process now.

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}? 

  Do you have any advice on how to solve this equation? Thanks a lot again for your help!

 
Antony