Notes on the Symmetries of 2-Layer ReLU-Networks

Symmetries in neural networks allow different weight configurations that lead to the same network function. For odd activation functions, the set of transformations mapping between such configurations has been studied extensively, but less is known for neural networks with ReLU activation functions. We give a complete characterization for fully-connected networks with two layers. Apart from two well-known transformations, only degenerated situations allow additional transformations that leave the network function unchanged. Finally, we present a non-degenerate situation for deep neural networks in which transformations exist that leave the network function intact.