A Geometric Theory for Binary Classification of Finite Datasets by DNNs with Relu Activations

In this paper we investigate deep neural networks for binary classification of datasets from geometric perspective in order to understand the working mechanism of deep neural networks. First, we establish a geometrical result on injectivity of finite set under a projection from Euclidean space to the real line. Then by introducing notions of alternative points and alternative number, we propose an approach to design DNNs for binary classification of finite labeled points on the real line, thus proving existence of binary classification neural net with its hidden layers of width two and the number of hidden layers not larger than the cardinality of the finite labelled set. We also demonstrate geometrically how the dataset is transformed across every hidden layers in a narrow DNN setting for binary classification task.