Dynamic Time Warping Under Translation: Approximation Guided by Space-Filling Curves

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The Dynamic Time Warping (DTW) distance is a popular measure of similarity for a variety of sequence data. For comparing polygonal curves p,s in Rd, it provides a robust, outlier-insensitive alternative to the Fréchet distance. However, like the Fréchet distance, the DTW distance is not invariant under translations. Can we efficiently optimize the DTW distance of p and s under arbitrary translations, to compare the curves' shape irrespective of their absolute location? There are surprisingly few works in this direction, which may be due to its computational intricacy: For the Euclidean norm, this problem contains as a special case the geometric median problem, which provably admits no exact algebraic algorithm (that is, no algorithm using only addition, multiplication, and k-th roots). We thus investigate exact algorithms for non-Euclidean norms as well as approximation algorithms for the Euclidean norm. For the L1 norm in Rd, we provide an O(n2(d+1))-time algorithm, i.e., an exact polynomial-time algorithm for constant d. Here and below, n bounds the curves' complexities. For the Euclidean norm in R2, we show that a simple problem-specific insight leads to a (1 + e)-approximation in time O(n3/e2). We then show how to obtain a subcubic Oe(n2.5/e2) time algorithm with significant new ideas; this time comes close to the well-known quadratic time barrier for computing DTW for fixed translations. Technically, the algorithm is obtained by speeding up repeated DTW distance estimations using a dynamic data structure for maintaining shortest paths in weighted planar digraphs. Crucially, we show how to traverse a candidate set of translations using space-filling curves in a way that incurs only few updates to the data structure. We hope that our results will facilitate the use of DTW under translation both in theory and practice, and inspire similar algorithmic approaches for related geometric optimization problems.

Original languageEnglish
Title of host publication38th International Symposium on Computational Geometry, SoCG 2022
EditorsXavier Goaoc, Michael Kerber
PublisherSchloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing
Publication date2022
Article number20
ISBN (Electronic)9783959772273
DOIs
Publication statusPublished - 2022
Event38th International Symposium on Computational Geometry, SoCG 2022 - Berlin, Germany
Duration: 7 Jun 202210 Jun 2022

Conference

Conference38th International Symposium on Computational Geometry, SoCG 2022
LandGermany
ByBerlin
Periode07/06/202210/06/2022
SeriesLeibniz International Proceedings in Informatics, LIPIcs
Volume224
ISSN1868-8969

Bibliographical note

Publisher Copyright:
© Karl Bringmann, Sndor Kisfaludi-Bak, Marvin Knnemann, Dniel Marx, and Andr Nusser; licensed under Creative Commons License CC-BY 4.0

    Research areas

  • Dynamic Time Warping, Sequence Similarity Measures

ID: 342673977