Abstract
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.
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Notes
For an overview of this literature see Rey and Le Gallo (2009) and references cited therein.
The decomposition here is with respect to pairs of observations \((i,j)\). Other decompositional approaches in the literature are taken with respect to subsets of the observations \(i=1,2,\ldots ,n\). See for example, D’Agostino and Dardanoni (2009).
GDP per capita is expressed in constant 1995 basis pesos.
Additional simulations explored the impact of ties on the relative performance of the alternative approaches. Ties do not affect the main quantitative or qualitative findings reported here. Results are available upon request.
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This research was funded by NSF Award OCI-1047916, SI2-SSI: CyberGIS Software Integration for Sustained Geospatial Innovation.
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Rey, S.J. Fast algorithms for a space-time concordance measure. Comput Stat 29, 799–811 (2014). https://doi.org/10.1007/s00180-013-0461-2
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DOI: https://doi.org/10.1007/s00180-013-0461-2