Abstract

We consider a group-theoretic analogue of the classic subset sum problem. In this brief note, we show that the subset sum problem is NP-complete in the first Grigorchuk group. More generally, we show NP-hardness of that problem in weakly regular branch groups, which implies NP-completeness if the group is, in addition, contracting.

Highlights

  • The study of discrete optimization problems in groups was initiated in [10], where the authors introduced group-theoretic generalizations of the classical knapsack problem and its variations, e.g., the subset sum problem and bounded submonoid membership problem.In the subsequent papers [13] and [14], the authors studied generalizations of the Post corresponce problem and classical lattice problems in groups

  • The Post correspondence problem in G is closely related to the twisted conjugacy problem in G, the equalizer problem in G, and a strong version of the word problem

  • Lattice problems are related to the classical subgroup membership problem and finite state automata

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Summary

Introduction

The study of discrete optimization problems in groups was initiated in [10], where the authors introduced group-theoretic generalizations of the classical knapsack problem and its variations, e.g., the subset sum problem and bounded submonoid membership problem. In the subsequent papers [13] and [14], the authors studied generalizations of the Post corresponce problem and classical lattice problems in groups. Lattice problems are related to the classical subgroup membership problem and finite state automata. We prove NP-hardness of the subset sum problem in any finitely generated weakly regular branch group. For groups with polynomial time word problem, e.g., the first Key words and phrases: Grigorchuk group, branch groups, subset sum problem, NP-completeness

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