# Electing a committee with dominance constraints

## TL;DR

This paper addresses the challenge of electing a committee under complex constraints, proposing methods to select the best valid committee despite NP-hardness, including polynomial and fixed-parameter tractable algorithms.

## Contribution

It extends the logic of weakly-separable and best-$k$ rules to order committees and provides algorithms for constrained committee selection.

## Key findings

- Polynomial time solution for tree-like constraints
- Fixed-parameter tractable algorithm for general constraints
- Framework for extending voting rules with dominance constraints

## Abstract

We consider the problem of electing a committee of $k$ candidates, subject to some constraints as to what this committee is supposed to look like. In our framework, the candidates are given labels as an abstraction of a politician's religion, a film's genre, a song's language, or other attribute, and the election outcome is constrained by interval constraints -- of the form "Between 3 and 5 candidates with label X" -- and dominance constraints -- "At least as many candidates with label X as with label Y". The problem is, what shall we do if the committee selected by a given voting rule fails these constraints? In this paper we argue how the logic underlying weakly-separable and best-$k$ rules can be extended into an ordering of committees, and study the question of how to select the best valid committee with respect to this order. The problem is NP-hard, but we show the existence of a polynomial time solution in the case of tree-like constraints, and a fixed-parameter tractable algorithm for the general case.