Functions for implementing the SPREAD algorithm for choosing fully factorial crossing sets

Functions used in the paper: Maximizing the mean nearest neighbor distance of a trait to choose among potential crosses and design a fully crossed mating experiment.

Description from the code comments:

This file contains two functions for selecting fully factorial crossing-sets from a larger set of all potential crosses for an outcrossing organism with two mating types or sexes. It is based on choosing crossing-sets with the maximum mean nearest neighbor distance of points representing crosses plotted on two dimensions of some characteristic of the cross (such as genetic and geographic distance between parents in a cross). The first function, StrainSampler, is not used by the user. It used in the second function, SpreadSelector, that is implemented by the user.

A pdf of the mathematical formalization of this algorithm is linked below