A Property Tester for Tree-Likeness of Quartet Topologies.

Property testing is a rapid growing field in theoretical computer science. It considers the following task: given a function f over a domain D, a property ℘ and a parameter 0< ε<1, by examining function values of f over o(| D|) elements in D, determine whether f satisfies ℘ or differs from any one which satisfies ℘ in at least ε| D| elements. An algorithm that fulfills this task is called a property tester. We focus on tree-likeness of quartet topologies, which is a combinatorial property originating from evolutionary tree construction. The input function is f, which assigns one of the three possible topologies for every quartet over an n-taxon set S. We say that f satisfies tree-likeness if there exists an evolutionary tree T whose induced quartet topologies coincide with f. In this paper, we prove the existence of a set of quartet topologies of error number at least $c{n\choose 4}$ for some constant c>0, and present the first property tester for tree-likeness of quartet topologies. Our property tester makes at most O( n/ ε) queries, and is of one-sided error and non-adaptive. [ABSTRACT FROM AUTHOR]