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... multi-dimensional indexing structures have been proposed to improve the multi-dimensional image databases performance. Most of the multi-dimensional indexing structures are based on the principle of hierarchical partitioning of the data space, so that they have a tree-like structure [4]. In these structures, as shown in Fig. 1, data points are stored in data nodes and each directory node points to a set of sub trees. There is a single directory node, which is called the root. The index structures are height-balanced; it means the lengths of the paths between the root and all data nodes are identical [3], ...

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... Then, a deep neural network is adopted to learn a set of hierarchi-cal nonlinear transformations, using back-propagation to map sample pairs into other subspace, where each positive sample pair is less than a smaller threshold 1 and that of each negative pair is higher than a larger threshold 2 , so that discriminative information is exploited for the robustness accuracy in unconstrained environmental images Most of them are not strong enough to obtain the nonlinear transformation wherever face images usually lie, as these methods use linear functions to project face representations to a new feature space. To solve this problem, some methods use the kernel trick, which is commonly used to first map face representations to feature space with high dimension and then learn the distance metric in the high dimensional feature space [12,21,47]. But these methods cannot capture the nonlinear functions to solve the problem of scalability. ...
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