Dynamics of learning near singularities in layered networks

  • Authors:
  • Haikun Wei;Jun Zhang;Florent Cousseau;Tomoko Ozeki;Shun-ichi Amari

  • Affiliations:
  • RIKEN Brain Science Institute, Saitama, 3510198, Japan, Southeast University, Nanjing, 210096, China, and Kyushu Institute of Technology, Kitakyushu 8080196, Japan. weihaikun@brain.riken.jp;RIKEN Brain Science Institute, Saitama, 3510198, Japan, and University of Michigan, Ann Arbor, MI 48109, U.S.A. junz@umich.edu;RIKEN Brain Science Institute, Saitama, 3510198, Japan, and University of Tokyo, Chiba, 2778561, Japan. florent@mns.k.u-tokyo.ac.jp;RIKEN Brain Science Institute, Saitama, 3510198, Japan, and Tokai University, Kanagawa, 2591292, Japan. tozeki@tokai.ac.jp;RIKEN Brain Science Institute, Saitama, 3510198, Japan. amari@brain.riken.jp

  • Venue:
  • Neural Computation
  • Year:
  • 2008

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Abstract

We explicitly analyze the trajectories of learning near singularities in hierarchical networks, such as multilayer perceptrons and radial basis function networks, which include permutation symmetry of hidden nodes, and show their general properties. Such symmetry induces singularities in their parameter space, where the Fisher information matrix degenerates and odd learning behaviors, especially the existence of plateaus in gradient descent learning, arise due to the geometric structure of singularity. We plot dynamic vector fields to demonstrate the universal trajectories of learning near singularities. The singularity induces two types of plateaus, the on-singularity plateau and the near-singularity plateau, depending on the stability of the singularity and the initial parameters of learning. The results presented in this letter are universally applicable to a wide class of hierarchical models. Detailed stability analysis of the dynamics of learning in radial basis function networks and multilayer perceptrons will be presented in separate work.