- #1
RJLiberator
Gold Member
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Homework Statement
Is there a non-degenerate 2x2 matrix that has only real eigenvalues but is not Hermitian? (Either find such a matrix, or prove that it doesn't exist)
Homework Equations
The Attempt at a Solution
Here's my problem. I'm getting Contradicting results.
So, I found this 2x2 matrix:
\begin{matrix}
1 & 2 \\
3 & 2
\end{matrix}
This matrix has eigenvalues of 4 and -1.
This matrix is not hermitian as the hermitian representation of this matrix transposes it.
Therefore this matrix is a 2x2 matrix that is non-degenerate and is NOT hermitian and has ONLY real eigenvalues.
This should be the example that the question was looking for.
However, in my notes, I have the equation for eigenvalues being
eigenvalue = [(a+b)+/- (squareroot ((a-b)^2-4cd))]/2
where
\begin{matrix}
a & c \\
d & b
\end{matrix}
And if we take this representation, we get negative eigenvalues.
What is going on here?