We prove that the LS category of the symplectic group $Sp(n)$ is bounded
above by $\binom{n+1}{2}$. This is achieved by computing the number of critical
levels of a height function.
We introduce the notion of characteristic function of a quaternionic matrix,
whose roots are the left eigenvalues. We prove that for all $2\times 2$
matrices and for $3\times 3$ matrices having some zero entry outside the
diagonal there is a characteristic function which satisfies Hamilton-Cayley
theorem.