Bounds on the number of hidden neurons in three-layer binary

  • Authors:
  • Zhaozhi Zhang;Xiaomin Ma;Yixian Yang

  • Affiliations:
  • Institute of Systems Science, Academia Sinica, Beijing 100080, People's Republic of China;Engineering and Physics Department, Oral Roberts University, Tulsa, OK;Engineering and Physics Department, Oral Roberts University, Tulsa, OK

  • Venue:
  • Neural Networks
  • Year:
  • 2003

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Abstract

This paper investigates an important problem concerning the complexity of three-layer binary neural networks (BNNs) with one hidden layer. The neuron in the studied BNNs employs a hard limiter activation function with only integer weights and an integer threshold. The studies are focused on implementations of arbitrary Boolean functions which map from {0, 1}n into {0, 1}. A deterministic algorithm called set covering algorithm (SCA) is proposed for the construction of a three-layer BNN to implement an arbitrary Boolean function. The SCA is based on a unit sphere covering (USC) of the Hamming space (HS) which is chosen in advance. It is proved that for the implementation of an arbitrary Boolean function of n-variables (n ≥ 3) by using SCA, ⌊3L/2⌋ hidden neurons are necessary and sufficient, where L is the number of unit spheres contained in the chosen USC of the n-dimensional HS. It is shown that by using SCA, the number of hidden neurons required is much less than that by using a two-parallel hyperplane method. In order to indicate the potential ability of three-layer BNNs, a lower bound on the required number of hidden neurons which is derived by using the method of estimating the Vapnik-Chervonenkis (VC) dimension is also given.