A geometric and combinatorial view of weighted voting

TL;DR

This paper explores the structure of weighted voting games through a geometric and combinatorial lens, introducing a polytope-based approach to analyze and compare these games and their properties.

Contribution

It presents a novel geometric framework linking polytopes to the poset of weighted games, and provides methods to determine weightedness and enumerate specific game types.

Findings

Maximal chains in the weighted games poset correspond to lines in the polytope union.

The polytope structure helps compare players' powers directly.

A method to determine weightedness of linear games using polytope facets.

Abstract

A natural partial ordering exists on the set of all weighted games and, more broadly, on all linear games. We describe several properties of the partially ordered sets formed by these games and utilize this perspective to enumerate proper linear games with one generator. We introduce a geometric approach to weighted voting by considering the convex polytope of all possible realizations of a weighted game and connect this geometric perspective to the weighted games poset in several ways. In particular, we prove that generic vertical lines in $C_n$, the union of all weighted $n$-player polytopes, correspond to maximal saturated chains in the poset of weighted games, i.e., the poset is a blueprint for how the polytopes fit together to form $C_n$. We show how to compare the relationships between the powers of the players using the polytope directly. Finally, we describe the facets of each polytope, from which we develop a method for determining the weightedness of any linear game that covers or is covered by a weighted game.