Abstract

Metric embeddings traditionally study how to map \(n\) items to a target metric space such that distance lengths are not heavily distorted; but what if we only care to preserve the relative order of the distances (and not their length)? In this paper, we are motivated by the following basic question: given triplet comparisons of the form ``item \(i\) is closer to item \(j\) than to item \(k\),'' can we find low-dimensional Euclidean representations for the \(n\) items that respect those distance comparisons? Such order-preserving embeddings naturally arise in important applications and have been studied since the 1950s, under the name of ordinal or non-metric embeddings. Our main results are: 1. Nearly-Tight Bounds on Triplet Dimension: We introduce the natural concept of triplet dimension of a dataset, and surprisingly, we show that in order for an ordinal embedding to be triplet-preserving, its dimension needs to grow as \(\frac n2\) in the worst case. This is optimal (up to consta

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