Definition 2

— In the notation of Prop. 4, the n monic polynomials $q_i(X)$ ($1 \leq i \leq n$) are called the similarity invariants of the endomorphism u.

Thus the n-th similarity invariant $q_n$ is the minimal polynomial of u (Prop. 4); in other words, for a polynomial $p(X) \in K[X]$ to satisfy $p(u) = 0$, it is necessary and sufficient that $p$ be a multiple of $q_n$.