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On the External Validity of Average-Case Analyses of Graph Algorithms

Authors Thomas Bläsius , Philipp Fischbeck

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Thomas Bläsius
  • Karlsruhe Institute of Technology (KIT), Germany
Philipp Fischbeck
  • Hasso Plattner Institute (HPI), University of Potsdam, Germany

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Thomas Bläsius and Philipp Fischbeck. On the External Validity of Average-Case Analyses of Graph Algorithms. In 30th Annual European Symposium on Algorithms (ESA 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 244, pp. 21:1-21:14, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2022)


The number one criticism of average-case analysis is that we do not actually know the probability distribution of real-world inputs. Thus, analyzing an algorithm on some random model has no implications for practical performance. At its core, this criticism doubts the existence of external validity, i.e., it assumes that algorithmic behavior on the somewhat simple and clean models does not translate beyond the models to practical performance real-world input. With this paper, we provide a first step towards studying the question of external validity systematically. To this end, we evaluate the performance of six graph algorithms on a collection of 2751 sparse real-world networks depending on two properties; the heterogeneity (variance in the degree distribution) and locality (tendency of edges to connect vertices that are already close). We compare this with the performance on generated networks with varying locality and heterogeneity. We find that the performance in the idealized setting of network models translates surprisingly well to real-world networks. Moreover, heterogeneity and locality appear to be the core properties impacting the performance of many graph algorithms.

Subject Classification

ACM Subject Classification
  • Theory of computation → Graph algorithms analysis
  • Theory of computation → Randomness, geometry and discrete structures
  • Average Case
  • Network Models
  • Empirical Evaluation


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