2018

On the Benefit of Width for Neural Networks: Disappearance of Bad Basins

Li, Dawei, Ding, Tian, Sun, Ruoyu

Understand

Wide networks are often believed to have a nice optimization landscape, but what rigorous results can we prove? To understand the benefit of width, it is important to identify the difference between wide and narrow networks.

  • In this work, we prove that from narrow to wide networks, there is a phase transition from having sub-optimal basins to no sub-optimal basins.
  • Specifically, we prove two results: on the positive side, for any continuous activation functions, the loss surface of a class of wide networks has no sub-optimal basins, where "basin" is defined as the set-wise strict local minimum; on the negative side, for a large class of networks with width below a threshold, we construct strict local minima that are not global.
  • These two results together show the phase transition from narrow to wide networks.

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