Normalized Gradient with Adaptive Stepsize Method for Deep Neural Network Training.

In this paper, we propose a generic and simple algorithmic framework for first order optimization. The framework essentially contains two consecutive steps in each iteration: 1) computing and normalizing the mini-batch stochastic gradient; 2) selecting adaptive step size to update the decision variable (parameter) towards the negative of the normalized gradient. We show that the proposed approach, when customized to the popular adaptive stepsize methods, such as AdaGrad, can enjoy a sublinear convergence rate, if the objective is convex. We also conduct extensive empirical studies on various non-convex neural network optimization problems, including multi layer perceptron, convolution neural networks and recurrent neural networks. The results indicate the normalized gradient with adaptive step size can help accelerate the training of neural networks. In particular, significant speedup can be observed if the networks are deep or the dependencies are long.