Error in the Euclidean Preference Model

Error in the Euclidean Preference Model

Luke Thorburn, Maria Polukarov, Carmine Ventre

Proceedings of the Thirty-Second International Joint Conference on Artificial Intelligence
Main Track. Pages 2888-2896. https://doi.org/10.24963/ijcai.2023/322

Spatial models of preference, in the form of vector embeddings, are learned by many deep learning and multiagent systems, including recommender systems. Often these models are assumed to approximate a Euclidean structure, where an individual prefers alternatives positioned closer to their "ideal point", as measured by the Euclidean metric. However, previous work has shown there are ordinal preference profiles that cannot be represented with this structure if the Euclidean space has two fewer dimensions than there are individuals or alternatives. We extend this result, showing that there are situations in which almost all preference profiles cannot be represented with the Euclidean model, and derive a theoretical lower bound on the expected error when using the Euclidean model to approximate non-Euclidean preference profiles. Our results have implications for the interpretation and use of vector embeddings, because in some cases close approximation of arbitrary, true ordinal relationships can be expected only if the dimensionality of the embeddings is a substantial fraction of the number of entities represented.
Keywords:
Game Theory and Economic Paradigms: GTEP: Computational social choice
Knowledge Representation and Reasoning: KRR: Preference modelling and preference-based reasoning
Machine Learning: ML: Learning preferences or rankings