From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Eigenvector of 2*2 symmetric and equal diagoal elements
Date: Sat, 26 May 2012 16:45:13 +0000 (UTC)
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"David " <> wrote in message <jpqtsm$k2n$>...
> Hi,
> I am trying to find the eigenvalue and eigenvector of a 2*2 matrix which is symmetric and have same diagonal elements. Even though I am changing the values of the matrix, the eigenvector remains same, only eigenvalues are changing. Why is this happening.

The sum along the rows of such a matrix will always be the same for every row. Hence [1;1] and its scalar multiples will always be an eigenvector. Similar ideas apply to the difference of the row elements.