Matroid Intersections, Polymatroid Inequalities, and Related Problems

  • Authors:
  • Endre Boros;Khaled M. Elbassioni;Vladimir Gurvich;Leonid Khachiyan

  • Affiliations:
  • -;-;-;-

  • Venue:
  • MFCS '02 Proceedings of the 27th International Symposium on Mathematical Foundations of Computer Science
  • Year:
  • 2002

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Abstract

Given m matroids M1,..., Mm on the common ground set V, it is shown that all maximal subsets of V, independent in the m matroids, can be generated in quasi-polynomial time. More generally, given a system of polymatroid inequalities f1(X) 驴 t1,..., fm(X) 驴 tm with quasi-polynomially bounded right hand sides t1,..., tm all minimal feasible solutions X 驴 V to the system can be generated in incremental quasi-polynomial time. Our proof of these results is based on a combinatorial inequality for polymatroid functions which may be of independent interest. Precisely, for a polymatroid function f and an integer threshold t 驴 1, let 驴 = 驴(f, t) denote the number of maximal sets X 驴 V satisfying f(X) t, let 脽 = 脽(f, t) be the number of minimal sets X 驴 V for which f(X) 驴 t, and let n = |V |. We show that 驴 驴 max{n, 脽(log t)/c}, where c = c(n, 脽) is the unique positive root of the equation 2c(nc/ log 脽 - 1) = 1. In particular, our bound implies that 驴 驴 (n脽)log t. We also give examples of polymatroid functions with arbitrarily large t, n, 驴 and 脽 for which 驴 = 脽(1-o(1)) log t/c.