A graph-theoretic result for a model of neural computation

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We deal in this work with the following graph construction problem that arises in a model of neural computation introduced by L.G. Valiant. For an undirected graph G = (V, E), let set N*(X, Y). where X, Y ⊆ V, denote the set of vertices other than those of X, Y which are adjacent to at least one vertex in X and at least one vertex in Y. An undirected graph G needs to be constructed that exhibits the following connectivity property. For any constant k and all disjoint sets A,B ⊆ V such that |A| = |B| = k, it is required that the cardinality of set C = N* (A, B) be k or as close to k as possible. We prove that for k > 1, if any graph G exists so that for all choices of A and B, set C = N* (A, B) has cardinality exactly k, then G must have exactly 3k vertices. Thus an exact solution for arbitrarily large values of n does not exist for any such k. A graph construction based on a projective plane graph provides an approximate solution, in a certain sense, for arbitrarily large n.

Original languageEnglish (US)
Pages (from-to)257-262
Number of pages6
JournalDiscrete Applied Mathematics
Issue number1-3
StatePublished - Mar 2 1998
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Discrete Mathematics and Combinatorics
  • Applied Mathematics


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