The resulting (v i , v j ) pairs of mesh vertices are written to a binary file along with the corresponding lagtime, ∆. For efficiency, all pairs are ordered so that the lower vertex index appears first (see for example the numbers highlighted in blue), and subsequently ordered along the first column, so that all particle displacements involving a given v i appear as a single contiguous block. Finally, the VTP algorithm needs to be called on each source vertex v i only once to evaluate all distances in the block. These evaluations are independent and therefore readily parallelized, as done in the current implementation. The computed displacements are assigned to both vertices while also taking account of the associated lagtime.