Integer Programming with GCD Constraints

TL;DR

This paper investigates the complexity and solution size bounds of integer programming problems with gcd constraints, establishing NP membership and polynomial bit length solutions using a local-to-global principle and a Chinese remainder theorem.

Contribution

It introduces a new fragment of the existential theory of integers with divisibility, proving feasibility is in NP and solutions have polynomial bit length, extending Lipshitz's local-to-global principle.

Findings

Feasibility problem for gcd-constrained systems is in NP.

Optimal solutions have polynomial bit length.

A Chinese-remainder-type theorem for systems of congruences and non-congruences is established.

Abstract

We study the non-linear extension of integer programming with greatest common divisor constraints of the form $\gcd(f,g) \sim d$, where $f$ and $g$ are linear polynomials, $d$ is a positive integer, and $\sim$ is a relation among $\leq, =, \neq$ and $\geq$. We show that the feasibility problem for these systems is in NP, and that an optimal solution minimizing a linear objective function, if it exists, has polynomial bit length. To show these results, we identify an expressive fragment of the existential theory of the integers with addition and divisibility that admits solutions of polynomial bit length. It was shown by Lipshitz [Trans. Am. Math. Soc., 235, pp. 271-283, 1978] that this theory adheres to a local-to-global principle in the following sense: a formula $\Phi$ is equi-satisfiable with a formula $\Psi$ in this theory such that $\Psi$ has a solution if and only if $\Psi$ has a solution modulo every prime $p$. We show that in our fragment, only a polynomial number of primes of polynomial bit length need to be considered, and that the solutions modulo prime numbers can be combined to yield a solution to $\Phi$ of polynomial bit length. As a technical by-product, we establish a Chinese-remainder-type theorem for systems of congruences and non-congruences showing that solution sizes do not depend on the magnitude of the moduli of non-congruences.