  Rectified linear unit (ReLU) is a widely used activation function for deep
convolutional neural networks. However, because of the zero-hard rectification,
ReLU networks miss the benefits from negative values. In this paper, we propose
a novel activation function called \emph{flexible rectified linear unit
(FReLU)} to further explore the effects of negative values. By redesigning the
rectified point of ReLU as a learnable parameter, FReLU expands the states of
the activation output. When the network is successfully trained, FReLU tends to
converge to a negative value, which improves the expressiveness and thus the
performance. Furthermore, FReLU is designed to be simple and effective without
exponential functions to maintain low cost computation. For being able to
easily used in various network architectures, FReLU does not rely on strict
assumptions by self-adaption. We evaluate FReLU on three standard image
classification datasets, including CIFAR-10, CIFAR-100, and ImageNet.
Experimental results show that the proposed method achieves fast convergence
and higher performances on both plain and residual networks.
