On the 2-sum embedding conjecture

  • Authors:
  • James R. Lee;Daniel E. Poore

  • Affiliations:
  • University of Washington, Seattle, WA, USA;University of Washington, Seattle, WA, USA

  • Venue:
  • Proceedings of the twenty-ninth annual symposium on Computational geometry
  • Year:
  • 2013

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Abstract

The 2-sum embedding conjecture (Lee-Sidiropoulos, FOCS 2009) states that all the shortest-path metrics supported on a family of graphs F admit a uniformly bi-Lipschitz embedding into L1 if and only if the same property holds for the closure of F under edge sums. The problem has an equivalent formulation in terms of multi-commodity flow/cut gaps and appears to be a fundamental step in resolving the well-studied question of which families of graphs admit an approximate multi-commodity max-flow/min-cut theorem. The 2-sum conjecture is known to be true when F = {K3}, where Kn denotes the complete graph on n vertices; this is equivalent to the seminal result of Gupta, Newman, Rabinovich, and Sinclair (Combinatorica, 2004) on embeddings of series-parallel graphs into L1. For F = {K4}, the conjecture was confirmed by Chakrabarti, Jaffe, Lee, and Vincent (FOCS 2008). In the present paper, we prove the conjecture holds for any finite family of graphs F. In fact, we obtain a quantitatively optimal result: Any path metric on a graph formed by 2-sums of arbitrarily many copies of Kn embeds into L1 with distortion O(log n). This is a consequence of a more general theorem that characterizes the L1 distortion of the 2-sum closure of any family F in terms of constrained embeddings of the members of F.