Computational complexity of reconstruction and isomorphism testing for designs and line graphs

  • Authors:
  • Michael Huber

  • Affiliations:
  • Wilhelm-Schickard-Institute for Computer Science, University of Tuebingen, Sand 13, D-72076 Tuebingen, Germany

  • Venue:
  • Journal of Combinatorial Theory Series A
  • Year:
  • 2011

Quantified Score

Hi-index 0.00

Visualization

Abstract

Graphs with high symmetry or regularity are the main source for experimentally hard instances of the notoriously difficult graph isomorphism problem. In this paper, we study the computational complexity of isomorphism testing for line graphs of t-(v,k,@l) designs. For this class of highly regular graphs, we obtain a worst-case running time of O(v^l^o^g^v^+^O^(^1^)) for bounded parameters t, k, @l. In a first step, our approach makes use of the Babai-Luks algorithm to compute canonical forms of t-designs. In a second step, we show that t-designs can be reconstructed from their line graphs in polynomial-time. The first is algebraic in nature, the second purely combinatorial. For both, profound structural knowledge in design theory is required. Our results extend earlier complexity results about isomorphism testing of graphs generated from Steiner triple systems and block designs.