Abstract
We show that the following two problems are fixed-parameter tractable with parameter \(k\): testing whether a connected \(n\)-vertex graph with \(m\) edges has a square root with at most \(n-1+k\) edges and testing whether such a graph has a square root with at least \(m-k\) edges. Our first result implies that squares of graphs obtained from trees by adding at most \(k\) edges can be recognized in polynomial time for every fixed \(k\ge 0\); previously this result was known only for \(k=0\). Our second result is equivalent to stating that deciding whether a graph can be modified into a square root of itself by at most \(k\) edge deletions is fixed-parameter tractable with parameter \(k\).
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Notes
We restrict ourselves to connected graphs for simplicity. We may do this for the following reason. For disconnected \(n\)-vertex graphs with \(\ell \ge 2\) connected components the natural parameter is \(k=s-(n-\ell )\) instead of \(k=s-(n-1)\). Our FPT result for connected graphs immediately carries over to disconnected graphs if we choose as parameter \(k=s-(n-\ell )\) instead.
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We would like to thank two anonymous reviewers for a number of helpful comments that improved our presentation.
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The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 267959. The research also has been supported by EPSRC (EP/G043434/1) and ANR Blanc AGAPE (ANR-09-BLAN-0159-03). A preliminary version of this paper appeared as an extended abstract in the proceedings of WG 2013 [4].
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Cochefert, M., Couturier, JF., Golovach, P.A. et al. Parameterized Algorithms for Finding Square Roots. Algorithmica 74, 602–629 (2016). https://doi.org/10.1007/s00453-014-9967-4
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DOI: https://doi.org/10.1007/s00453-014-9967-4