Fast algorithms for a space-time concordance measure

This paper presents a number of algorithms for a recently developed measure of space-time concordance. Based on a spatially explicit version of Kendall’s \(\tau \) the original implementation of the concordance measure relied on a brute force \(O(n^2)\) algorithm which has limited its use to modest sized problems. Several new algorithms have been devised which move this run time to \(O(n log(n) +np)\) where \(p\) is the expected number of spatial neighbors for each unit. Comparative timing of these alternative implementations reveals dramatic efficiency gains in moving away from the brute force algorithms. A tree-based implementation of the spatial concordance is also found to dominate a merge sort implementation.