Drawing (Complete) Binary Tanglegrams. Buchin, K., Buchin, M., Byrka, J., Nöllenburg, M., Okamoto, Y., Silveira, R., & Wolff, A. Algorithmica, 62(1):309–332, Springer New York, 2012.
doi  abstract   bibtex   
A binary tanglegram is a drawing of a pair of rooted binary trees whose leaf sets are in one-to-one correspondence; matching leaves are connected by inter-tree edges. For applications, for example, in phylogenetics, it is essential that both trees are drawn without edge crossings and that the inter-tree edges have as few crossings as possible. It is known that finding a tanglegram with the minimum number of crossings is NP-hard and that the problem is fixed-parameter tractable with respect to that number. We prove that under the Unique Games Conjecture there is no constant-factor approximation for binary trees. We show that the problem is NP-hard even if both trees are complete binary trees. For this case we give an O ( n 3 )-time 2-approximation and a new, simple fixed-parameter algorithm. We show that the maximization version of the dual problem for binary trees can be reduced to a version of MaxCut for which the algorithm of Goemans and Williamson yields a 0.878-approximation.
@Article{buchin12drawing,
  author      = {Buchin, Kevin and Buchin, Maike and Byrka, Jaroslaw and N\"ollenburg, Martin and Okamoto, Yoshio and Silveira, Rodrigo and Wolff, Alexander},
  title       = {Drawing (Complete) Binary Tanglegrams},
  journal     = {Algorithmica},
  year        = {2012},
  volume      = {62},
  number      = {1--2},
  pages       = {309--332},
  issn        = {0178-4617},
  abstract    = {A binary tanglegram is a drawing of a pair of rooted binary trees whose leaf sets are in one-to-one correspondence; matching leaves are connected by inter-tree edges. For applications, for example, in phylogenetics, it is essential that both trees are drawn without edge crossings and that the inter-tree edges have as few crossings as possible. It is known that finding a tanglegram with the minimum number of crossings is NP-hard and that the problem is fixed-parameter tractable with respect to that number. We prove that under the Unique Games Conjecture there is no constant-factor approximation for binary trees. We show that the problem is NP-hard even if both trees are complete binary trees. For this case we give an O ( n 3 )-time 2-approximation and a new, simple fixed-parameter algorithm. We show that the maximization version of the dual problem for binary trees can be reduced to a version of MaxCut for which the algorithm of Goemans and Williamson yields a 0.878-approximation.},
  affiliation = {Faculteit Wiskunde en Informatica, TU Eindhoven, Eindhoven, The Netherlands},
  doi         = {10.1007/s00453-010-9456-3},
  number      = {1},
  keyword     = {Informatik},
  keywords    = {fpt; tanglegrams},
  owner       = {Sebastian},
  publisher   = {Springer New York},
  timestamp   = {2012.02.07},
}

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