The interval ordering problem

TL;DR

This paper studies the interval ordering problem, aiming to minimize exposed interval pieces, with applications in protein structure determination, providing polynomial algorithms for special cases and proving NP-hardness of the general problem.

Contribution

Introduces polynomial-time algorithms for specific cases of the interval ordering problem and establishes NP-hardness for the general case.

Findings

Polynomial algorithms for agreeably ordered and laminar interval sets

Bottleneck variant solvable in polynomial time

General problem proven NP-hard with no constant-factor approximation likely

Abstract

For a given set of intervals on the real line, we consider the problem of ordering the intervals with the goal of minimizing an objective function that depends on the exposed interval pieces (that is, the pieces that are not covered by earlier intervals in the ordering). This problem is motivated by an application in molecular biology that concerns the determination of the structure of the backbone of a protein. We present polynomial-time algorithms for several natural special cases of the problem that cover the situation where the interval boundaries are agreeably ordered and the situation where the interval set is laminar. Also the bottleneck variant of the problem is shown to be solvable in polynomial time. Finally we prove that the general problem is NP-hard, and that the existence of a constant-factor-approximation algorithm is unlikely.