Lower Bounds for Electrical Reduction on Surfaces

Authors Hsien-Chih Chang, Marcos Cossarini, Jeff Erickson

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Hsien-Chih Chang
  • Duke University, Durham, USA
Marcos Cossarini
  • Laboratoire d'Analyse et de Mathématiques Appliquées, Université Paris-Est Marne-la-Vallée, Champs-sur-Marne, France
Jeff Erickson
  • University of Illinois at Urbana-Champaign, Champaign, USA

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Hsien-Chih Chang, Marcos Cossarini, and Jeff Erickson. Lower Bounds for Electrical Reduction on Surfaces. In 35th International Symposium on Computational Geometry (SoCG 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 129, pp. 25:1-25:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


We strengthen the connections between electrical transformations and homotopy from the planar setting - observed and studied since Steinitz - to arbitrary surfaces with punctures. As a result, we improve our earlier lower bound on the number of electrical transformations required to reduce an n-vertex graph on surface in the worst case [SOCG 2016] in two different directions. Our previous Omega(n^{3/2}) lower bound applies only to facial electrical transformations on plane graphs with no terminals. First we provide a stronger Omega(n^2) lower bound when the planar graph has two or more terminals, which follows from a quadratic lower bound on the number of homotopy moves in the annulus. Our second result extends our earlier Omega(n^{3/2}) lower bound to the wider class of planar electrical transformations, which preserve the planarity of the graph but may delete cycles that are not faces of the given embedding. This new lower bound follow from the observation that the defect of the medial graph of a planar graph is the same for all its planar embeddings.

Subject Classification

ACM Subject Classification
  • Theory of computation → Design and analysis of algorithms
  • electrical transformation
  • Delta-Y-transformation
  • homotopy
  • tight
  • defect
  • SPQR-tree
  • smoothings
  • routing set
  • 2-flipping


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