Path: news.mathworks.com!not-for-mail
From: "John D'Errico" <woodchips@rochester.rr.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: unsorted eigenvalues
Date: Sun, 18 Nov 2007 12:51:42 +0000 (UTC)
Organization: John D'Errico (1-3LEW5R)
Lines: 35
Message-ID: <fhpcgu$7lf$1@fred.mathworks.com>
References: <fdhvq6$hok$1@fred.mathworks.com> <fdit8b$5r1$1@fred.mathworks.com> <fhp882$d8h$1@fred.mathworks.com> <fhpb69$k4u$1@fred.mathworks.com>
Reply-To: "John D'Errico" <woodchips@rochester.rr.com>
NNTP-Posting-Host: webapp-02-blr.mathworks.com
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-Trace: fred.mathworks.com 1195390302 7855 172.30.248.37 (18 Nov 2007 12:51:42 GMT)
X-Complaints-To: news@mathworks.com
NNTP-Posting-Date: Sun, 18 Nov 2007 12:51:42 +0000 (UTC)
X-Newsreader: MATLAB Central Newsreader 869215
Xref: news.mathworks.com comp.soft-sys.matlab:438202



"Masakazu Iwamura" <masa@AHOAHOcs.osakafu-u.ac.jp> wrote in message 
<fhpb69$k4u$1@fred.mathworks.com>...
> Hi,
> 
> > Here is the answer:
> > 
> > C=cov(some_data);
> > [V,D]=eig(C);
> > unsorted_eigenvalues=V'*C*V;
> 
> This seems to be my misunderstanding. I couldn't get what I
> want:(

The problem is in your wish for something
that is "unsorted".

A sorted vector means that it has a definite,
known order. Unsorted merely means that
this ordering has not been applied. It does
not mean that you will get any desired
ordering. The ordering may then be arbitrary,
which is not what you seem to be wishing
for.

What people seem to want when they ask
for unsorted eigenvalues is their OWN
(magically chosen) ordering for the 
eigenvalues. However, the eigenvalue
code cannot understand this, or know
that ordering. The eigenvalues are merely
a set of polynomial roots in the complex
plane.

John