Deterministic Polynomial-time Exact-root Computation for Sparse Polynomials with Bounded Total Degree

2026-07-02

AI Summary

This work addresses the exact root problem for $n$-variate $s$-sparse polynomials $f$ whose total degree is bounded by $D$: given $f = g^e$, the goal is to efficiently recover the base polynomial $g$. We present the first deterministic polynomial-time algorithm for this setting, overcoming prior limitations that only achieved quasipolynomial complexity. Our approach integrates sparsity analysis, algebraic structural constraints, and root-finding over fields, combining combinatorial and algebraic techniques to establish an upper bound on the sparsity of $g$ and to reconstruct it efficiently. The algorithm runs in time $\mathrm{poly}(s^{O(Dd)}, n, d, D) + s \cdot R(e)$, achieving deterministic polynomial-time performance over common fields such as finite fields and the rationals.

Abstract

We study the problem of deterministically computing the exact root of a sparse polynomial in the multivariate setting. Let $f \in \F[x_1,\ldots,x_n]$ be a nonzero polynomial that is an exact $e$-th power, say $f = g^e$. Suppose $f$ is $s$-sparse, has an individual degree of at most $d$, and a total degree of $D = \tdeg(f)$. We prove a sparsity bound on the base polynomial $g$: \[ \|g\|_0 \le s^{D(2d+2)/e + 1}. \] Based on this bound, we develop a deterministic algorithm that computes the base $g$. % In contrast to the general deterministic factorization algorithm of Bhargava, Saraf, and Volkovich \cite{BhargavaSarafVolkovich2020}, which achieves only a quasi-polynomial dependence on the input parameters, our algorithm is \emph{polynomial-time} in the setting where the total degree $D$ is bounded. Specifically, the overall complexity is \[ \mathrm{poly}\left(s^{O(Dd)}, n, d, D\right) + s\cdot R(e), \] % where $R(e)$ denotes the cost of constructing a single $e$-th root of a scalar in the base field $\F$, and, when $\operatorname{char}(\F)\mid e$, the cost of computing a single Frobenius root of a scalar. % This term is field-dependent, and over finite fields, $\mathbb{Q}$, or number fields with a suitable representation, it is absorbed into the polynomial complexity bound. % Within the bounded total-degree regime, this yields a deterministic polynomial-time algorithm for exact-root computation.

Problem

• sparse polynomials
• exact-root computation
• deterministic algorithm
• bounded total degree
• multivariate polynomials

Innovation

• sparse polynomials
• exact-root computation
• deterministic algorithm
• polynomial-time
• bounded total degree