Growth of bilinear maps II: Bounds and orders

Abstract

A good range of problems on trees can be described by the following general setting: Given a bilinear map $*:\mathbb R^d\times\mathbb R^d\to\mathbb R^d$ and a vector $s\in\mathbb R^d$, we need to estimate the largest possible absolute value $g(n)$ of an entry over all vectors obtained from applying $n-1$ applications of $*$ to $n$ instances of $s$. When the coefficients of $*$ are nonnegative and the entries of $s$ are positive, the value $g(n)$ is known to follow a growth rate $\lambda=\lim_{n\to\infty} \sqrt[n]{g(n)}$. In this article, we prove that for such $*$ and $s$ there exist nonnegative numbers $r,r'$ and positive numbers $a,a'$ so that for every $n$, \[ a n^{-r}\lambda^n\le g(n)\le a' n^{r'}\lambda^n. \] While proving the upper bound, we actually also provide another approach in proving the limit $\lambda$ itself. The lower bound is proved by showing a certain form of submultiplicativity for $g(n)$. Corollaries include a lower bound and an upper bound for $\lambda$, which are followed by a good estimation of $\lambda$ when we have the value of $g(n)$ for an $n$ large enough.