Earthmover Resilience and Testing in Ordered Structures

TL;DR

This paper introduces earthmover resilient (ER) properties for ordered structures, enabling constant-query property testing similar to unordered graphs, and applies this to estimate distances to hereditary properties in images and ordered graphs.

Contribution

It defines ER properties for ordered structures and demonstrates their testability with constant queries, extending unordered graph results to more complex ordered data.

Findings

ER properties include all unordered graph properties and many visual properties.

Constant-query algorithms can estimate distances to hereditary properties in images and ordered graphs.

ER properties facilitate property testing in ordered structures, broadening applicability.

Abstract

One of the main challenges in property testing is to characterize those properties that are testable with a constant number of queries. For unordered structures such as graphs and hypergraphs this task has been mostly settled. However, for ordered structures such as strings, images, and ordered graphs, the characterization problem seems very difficult in general. In this paper, we identify a wide class of properties of ordered structures - the earthmover resilient (ER) properties - and show that the "good behavior" of such properties allows us to obtain general testability results that are similar to (and more general than) those of unordered graphs. A property P is ER if, roughly speaking, slight changes in the order of the elements in an object satisfying P cannot make this object far from P. The class of ER properties includes, e.g., all unordered graph properties, many natural visual properties of images, such as convexity, and all hereditary properties of ordered graphs and images. A special case of our results implies, building on a recent result of Alon and the authors, that the distance of a given image or ordered graph from any hereditary property can be estimated (with good probability) up to a constant additive error, using a constant number of queries.