On the complexity of submodular function minimisation on diamonds

  • Authors:
  • Fredrik Kuivinen

  • Affiliations:
  • -

  • Venue:
  • Discrete Optimization
  • Year:
  • 2011

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Abstract

Let (L;@?,@?) be a finite lattice and let n be a positive integer. A function f:L^n-R is said to be submodular if f(a@?b)+f(a@?b)@?f(a)+f(b) for all a,b@?L^n. In this article we study submodular functions when L is a diamond. Given oracle access to f we are interested in finding x@?L^n such that f(x)=min"y"@?"L"^"nf(y) as efficiently as possible. We establish *a min-max theorem, which states that the minimum of the submodular function is equal to the maximum of a certain function defined over a certain polyhedron; and *a good characterisation of the minimisation problem, i.e., we show that given an oracle for computing a submodular f:L^n-Z and an integer m such that min"x"@?"L"^"nf(x)=m, there is a proof of this fact which can be verified in time polynomial in n and max"t"@?"L"^"nlog|f(t)|; and *a pseudopolynomial-time algorithm for the minimisation problem, i.e., given an oracle for computing a submodular f:L^n-Z one can find min"t"@?"L"^"nf(t) in time bounded by a polynomial in n and max"t"@?"L"^"n|f(t)|.