Consensus Division in an Arbitrary Ratio

Abstract

We consider the problem of partitioning a line segment into two subsets, so that n finite measures all has the same ratio of values for the subsets. Letting α ∈ [0, 1] denote the desired ratio, this generalises the PPA-complete consensushalving problem, in which α = 1 2 . It is known that for any α, there exists a solution using 2n cuts of the segment. Here we show that if α is irrational, that upper bound is almost optimal. We also obtain bounds that are nearly exact for a large subset of rational values α. On the computational side, we explore its dependence on the number of cuts available. More specifically, 1. when using the minimal number of cuts for each instance is required, the problem is NP-hard for any α;2. for a large subset of rational α = k , when k−1 k • 2n cuts are available, the problem is in the Turing closure of PPA-k; 3. when 2n cuts are allowed, the problem belongs to PPA for any α; furthermore, the problem belong to PPA-p for any prime p if 2(p − 1) • p/2 p/2 • n cuts are available.