Exponentiality of the exchange algorithm for finding another room-partitioning

Jack Edmonds, Laura Sanità

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)


Let T be a triangulated surface given by the list of vertex-triples of its triangles, called rooms. A room-partitioning for T is a subset R of the rooms such that each vertex of T is in exactly one room in R. Given a room-partitioning R for T, the exchange algorithm walks from room to room until it finds a second different room-partitioning R′. In fact, this algorithm generalizes the Lemke-Howson algorithm for finding a Nash equilibrium for two-person games. In this paper, we show that the running time of the exchange algorithm is not polynomial relative to the number of rooms, by constructing a sequence of (planar) instances, in which the algorithm walks from room to room an exponential number of times. We also show a similar result for the problem of finding a second perfect matching in Eulerian graphs.

Original languageEnglish
Pages (from-to)86-91
Number of pages6
JournalDiscrete Applied Mathematics
Issue numberPART 1
Publication statusPublished - 1 Jan 2014


  • Exchange algorithm
  • Room-partitioning
  • Two-person games


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