Solution (source code)

= Solution

Computing the <characteristic polynomial> with the convention $\det(\lambda I-H)$ gives
$$
\det(\lambda I-H)=\lambda(\lambda+1)(\lambda-3).
$$
Thus the three <eigenvalues> are
$$
\boxed{-1,\quad0,\quad3.}
$$
They can also be checked directly on the respective <eigenvectors> $(1,0,-1)^T$, $(1,-1,1)^T$, and $(1,2,1)^T$.