Dividing a Graphical Cake

TL;DR

This paper extends the classical cake-cutting problem to graph-structured resources, analyzing fairness and welfare guarantees for dividing such resources among agents with various constraints.

Contribution

It introduces a generalized graph-based cake division model, determines optimal fairness approximations, and explores multiple variants including chore division.

Findings

Optimal proportionality approximation for any number of agents.

Tight fairness guarantees for two agents on specific graphs.

Best egalitarian welfare guarantees with multiple connected pieces.

Abstract

We consider the classical cake-cutting problem where we wish to fairly divide a heterogeneous resource, often modeled as a cake, among interested agents. Work on the subject typically assumes that the cake is represented by an interval. In this paper, we introduce a generalized setting where the cake can be in the form of the set of edges of an undirected graph. This allows us to model the division of road or cable networks. Unlike in the canonical setting, common fairness criteria such as proportionality cannot always be satisfied in our setting if each agent must receive a connected subgraph. We determine the optimal approximation of proportionality that can be obtained for any number of agents with arbitrary valuations, and exhibit tight guarantees for each graph in the case of two agents. In addition, when more than one connected piece per agent is allowed, we establish the best egalitarian welfare guarantee for each total number of connected pieces. We also study a number of variants and extensions, including when approximate equitability is considered, or when the item to be divided is undesirable (also known as chore division).