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Abstract : |
The doubling constant of a metric space (X, d) is the smallest value # such that every ball in X can be covered by # balls of half the radius. The doubling dimension of X is then defined as dim(X) = log 2 #. A metric (or sequence of metrics) is called doubling precisely when its doubling dimension is bounded. This is a robust class of metric spaces which contains many families of metrics that occur in applied settings. We give tight bounds for embedding doubling metrics into (low-dimensional) normed spaces. We consider both general doubling metrics, as well as more restricted families such as those arising from trees, from graphs excluding a fixed minor, and from snowflaked metrics. Our techniques include decomposition theorems for doubling metrics, and an analysis of a fractal in the plane due to Laakso [20]. Finally, we discuss some applications and point out a central open question regarding dimensionality reduction in L 2., |
