Intersection representations of matrices by subtrees and unicycles on graphs

  • Authors:
  • Fanica Gavril;Ron Y. Pinter;Shmuel Zaks

  • Affiliations:
  • Department of Computer Science, Technion, Haifa 32000, Israel;Department of Computer Science, Technion, Haifa 32000, Israel;Department of Computer Science, Technion, Haifa 32000, Israel

  • Venue:
  • Journal of Discrete Algorithms
  • Year:
  • 2008

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Abstract

Consider a 0-1 matrix M(i,j) with columns C={c"1,c"2,...,c"m}, and rows R, or-equivalently-a hypergraph M(R,C) having M as its adjacency matrix (where R are the vertices and C are the hyperedges). Denote r"i={c"j|c"j@?C and M(i,j)=1}. We consider the following two problems: (a) Is there a graph H, with vertex set C, such that every vertex subgraph H(r"i) of H is a tree and the intersection of every two such trees is also a tree? (b) Is there a graph H, with vertex set C, such that every H(r"i) is a unicycle and the intersection of every two and every three unicycles is a tree? These questions occur in application areas such as database management systems and computational biology; e.g., in the latter they arise in the context of the analysis of biological networks, primarily for the purpose of data clustering. We describe algorithms to find such intersection representations of a matrix M (and equivalently of the hypergraph M), when they exist.