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### Paper:

TR20-092 | 16th June 2020 08:56

#### Computing Igusa's local zeta function of univariates in deterministic polynomial-time

TR20-092
Authors: Ashish Dwivedi, Nitin Saxena
Publication: 16th June 2020 11:32
Igusa's local zeta function $Z_{f,p}(s)$ is the generating function that counts the number of integral roots, $N_{k}(f)$, of $f(\mathbf x) \bmod p^k$, for all $k$. It is a famous result, in analytic number theory, that $Z_{f,p}$ is a rational function in $\mathbb{Q}(p^s)$. We give an elementary proof of this fact for a univariate polynomial $f$. Our proof is constructive as it gives a closed-form expression for the number of roots $N_{k}(f)$.
Our proof, when combined with the recent root-counting algorithm of (Dwivedi, Mittal, Saxena, CCC, 2019), yields the first deterministic poly($|f|, \log p$) time algorithm to compute $Z_{f,p}(s)$. Previously, an algorithm was known only in the case when $f$ completely splits over $\mathbb{Q_p}$; it required the rational roots to use the concept of generating function of a tree (Zuniga-Galindo, J.Int.Seq., 2003).