Path: news.mathworks.com!not-for-mail 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 02:26:04 +0000 (UTC) Organization: Anhui University Lines: 18 Message-ID: <i2irns$94i$1@fred.mathworks.com> References: <i2he90$21a$1@fred.mathworks.com> <i2i2st$n4j$1@fred.mathworks.com> Reply-To: <HIDDEN> NNTP-Posting-Host: webapp-02-blr.mathworks.com Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Trace: fred.mathworks.com 1280111164 9362 172.30.248.37 (26 Jul 2010 02:26:04 GMT) X-Complaints-To: news@mathworks.com NNTP-Posting-Date: Mon, 26 Jul 2010 02:26:04 +0000 (UTC) X-Newsreader: MATLAB Central Newsreader 2419503 Xref: news.mathworks.com comp.soft-sys.matlab:656051 "Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <i2i2st$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