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Title: Optimistic Acceleration for Optimization

Paper content:
We consider new variants of optimization algorithms.
Our algorithms are based on the observation that mini-batch of stochastic gradients in consecutive iterations do not change drastically and consequently may be predictable.
Inspired by the similar setting in online learning literature called Optimistic Online learning, we propose two new optimistic algorithms for AMSGrad and Adam, respectively, by  exploiting the predictability of gradients.
The new algorithms combine the idea of momentum method, adaptive gradient method, and algorithms in Optimistic Online learning, which leads to speed up in training deep neural nets in practice.
Nowadays deep learning has been shown to be very effective in several tasks, from robotics (e.g. BID15 ), computer vision (e.g. BID12 ; BID9 ), reinforcement learning (e.g. BID18 , to natural language processing (e.g. ).
Typically, the model parameters of a state-of-the-art deep neural net is very high-dimensional and the required training data is also in huge size.
Therefore, fast algorithms are necessary for training a deep neural net.
To achieve this, there are number of algorithms proposed in recent years, such as AMSGRAD (Reddi et al. (2018) ), ADAM BID13 ), RMSPROP (Tieleman & Hinton (2012) ), ADADELTA (Zeiler (2012) ), and NADAM BID6 ), etc.All the prevalent algorithms for training deep nets mentioned above combines two ideas: the idea of adaptivity in ADAGRAD BID7 BID17 ) and the idea of momentum as NESTEROV'S METHOD BID19 ) or the HEAVY BALL method BID20 ).
ADAGRAD is an online learning algorithm that works well compared to the standard online gradient descent when the gradient is sparse.
The update of ADAGRAD has a notable feature: the learning rate is different for different dimensions, depending on the magnitude of gradient in each dimension, which might help in exploiting the geometry of data and leading to a better update.
On the other hand, NESTEROV'S METHOD or the Momentum Method BID20 ) is an accelerated optimization algorithm whose update not only depends on the current iterate and current gradient but also depends on the past gradients (i.e. momentum).
State-of-the-art algorithms like AMSGRAD (Reddi et al. (2018) ) and ADAM BID13 ) leverages these two ideas to get fast training for neural nets.In this paper, we propose an algorithm that goes further than the hybrid of the adaptivity and momentum approach.
Our algorithm is inspired by OPTIMISTIC ONLINE LEARNING BID4 ; Rakhlin & Sridharan (2013) ; Syrgkanis et al. (2015) ; BID0 ).
OPTIMISTIC ONLINE LEARNING considers that a good guess of the loss function in the current round of online learning is available and plays an action by exploiting the good guess.
By exploiting the guess, those algorithms in OPTIMISTIC ONLINE LEARNING have regret in the form of O( T t=1 g t − m t ), where g t is the gradient of loss function in round t and m t is the "guess" of g t before seeing the loss function in round t (i.e. before getting g t ).
This kind of regret can be much smaller than O( √ T ) when one has a good guess m t of g t .
We combine the OPTIMISTIC ONLINE LEARNING idea with the adaptivity and the momentum ideas to design new algorithms in training deep neural nets, which leads to NEW-OPTIMISTIC-AMSGRAD and NEW-OPTIMISTIC-ADAM.
We also provide theoretical analysis of NEW-OPTIMISTIC-AMSGRAD.
The proposed OPTIMISTIC-algorithms not only adapt to the informative dimensions and exhibit momentums but also take advantage of a good guess of the next gradient to facilitate acceleration.
We evaluate our algorithms with BID13 ), (Reddi et al. (2018) ) and BID5 ).
Experiments show that our OPTIMISTIC-algorithms are faster than the baselines.
We should explain that BID5 proposed another version of optimistic algorithm for ADAM, which is referred to as ADAM-DISZ in this paper.
We apply the idea of BID5 ) on AMSGRAD, which leads to AMSGRAD-DISZ.
Both ADAM-DISZ and AMSGRAD-DISZ are used as baselines.

assistant: text: We consider new variants of optimization algorithms for training deep nets.