Clique-Width is NP-Complete

  • Authors:
  • Michael R. Fellows;Frances A. Rosamond;Udi Rotics;Stefan Szeider

  • Affiliations:
  • michael.fellows@newcastle.edu.au and frances.rosamond@newcastle.edu.au;-;rotics@mars.netanya.ac.il;stefan.szeider@durham.ac.uk

  • Venue:
  • SIAM Journal on Discrete Mathematics
  • Year:
  • 2009

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Abstract

Clique-width is a graph parameter that measures in a certain sense the complexity of a graph. Hard graph problems (e.g., problems expressible in monadic second-order logic with second-order quantification on vertex sets, which includes NP-hard problems such as 3-colorability) can be solved in polynomial time for graphs of bounded clique-width. We show that the clique-width of a given graph cannot be absolutely approximated in polynomial time unless $P = NP$. We also show that, given a graph $G$ and an integer $k$, deciding whether the clique-width of $G$ is at most $k$ is NP-complete. This solves a problem that has been open since the introduction of clique-width in the early 1990s.