1. A computation system for computing interactions in a multiple-body simulation, said system comprising an array of processing nodes that are connected to each other, wherein each processing node of said array of processing nodes comprises an array of processing modules arranged into one or more serially interconnected processing groups of the processing modules, wherein each of said groups is serially interconnected in only one dimension, wherein processing modules in each group are not connected to processing modules in other groups, wherein each of the processing modules includes a storage element for data elements and circuitry for performing pairwise computations between data elements each associated with a spatial location, each of the pairwise computations making use of a data element from the storage element of the processing module and a data element passing through the serially interconnected processing modules, and circuitry for selecting the pairs of data elements according to separations between spatial locations associated with the data elements.