Let U be a set of elements and d a distance function defined among them. Let NN k (u) be the k elements in U − {u} having the smallest distance to u. The k-nearest neighbor graph (knng) is a weighted Several knng construction algorithms are known, but they are not suitable to general metric spaces. We present a general methodology to construct knngs that exploits several features of metric spaces. Experiments suggest that it yields costs of the form c1n 1.27 distance computations for low and

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... ium dimensional spaces, and c2n 1.90 for high dimensional ones. ⋆