We know that symmetric matrices are orthogonally diagonalizable and have real eigenvalues. Is the converse true? Does a matrix with real eigenvalues have to be symmetric?
A class of symmetric matrices, the positive definite matrices, have positive real eigenvalues. Is the converse true? Does a matrix with positive real eigenvalues have to be symmetric, positive-definite?
I think the answer to all this is "no", but I just wanted to confirm.
Thanks,
Best Answer
Is the matrix
$$\begin{pmatrix}1&1\\0&1\end{pmatrix}$$
symmetric? It has only one positive eigenvalue of multiplicity two.