arXiv subjects
Publications and source records attributed to Zhaoning Yang.
This note describes a Macaulay2 package for handling divisors. Group operations for divisors are included. There are methods for converting divisors to reflexive or invertible sheaves. Additionally, there are methods for checking whether divisors are Cartier, $Q$-Cartier, simple normal crossings, generate base point free linear systems, or satisfy numerous other conditions.
Let $f(x) \in \mathbb{C}[x]$ of degree $n$. We attach to $f$ a $\mathbb{C}$-vector space $W(f)$ which consists of complex polynomials $p(x)$ of degree at most $n - 2$ such that $f(x)$ divides $f"(x)p(x) - f'(x) p'(x)$. The space $W(f)$ originally appears in Yuri Zarhin's solution towards a problem of dynamics in one complex variable posed by Yu. S. Ilyashenko. In this paper, we show that $W(f)$ is nonvanishing if and only if $q(x)^2$ divides $f(x)$ for some quadratic polynomial $q(x)$. Then we prove $W(f)$ has dimension $(n-1) - (n_1 + n_2 + 2N_3)$ under certain conditions, where $n_i$ is the number of distinct roots of $f$ with multiplicity $i$ and $N_3$ is the number of distinct roots of $f$ with multiplicity at least three.