LiSHT

This repository contains a Keras implementation of the paper "LiSHT: Non-Parametric Linearly Scaled Hyperbolic Tangent Activation Function for Neural Networks" - (link to the arXiv page)

Roy, Kumar S., Manna, S., Dubey, Ram S., and Chaudhuri, Baran B., 2019. LiSHT: Non-Parametric Linearly Scaled 
Hyperbolic Tangent Activation Function for Neural Networks. arXiv preprint arXiv:1901.05894.

Description

The activation function in neural network is one of the important aspects which facilitates the deep training by introducing the non-linearity into the learning process. However, because of zero-hard rectification, some the of existing activations function such as ReLU and Swish miss to utilize the negative input values and may suffer from the dying gradient problem. Thus, it is important to look for a better activation function which is free from such problems. As a remedy, this paper proposes a new non-parametric function, called Linearly Scaled Hyperbolic Tangent (LiSHT) for Neural Networks (NNs). The proposed LiSHT activation function is an attempt to scale the non-linear Hyperbolic Tangent (Tanh) function by a linear function and tackle the dying gradient problem.

What is a LiSHT?

Most neural networks work by interleaving linear projections and simple (fixed) activation functions, like the ReLU function:

A LiSHT is instead a parametric activation function defined as non-parametric approximator:

Pre-Activation ResNet

Experimental Data

The effectiveness of the proposed LiSHT activation function is evaluated on six benchmark datasets:

• Car Evaluation Dataset
• Iris Flower Dataset
• MNIST Dataset
• CIFAR-10 Dataset
• CIFAR-100 Dataset
• Twitter140 Dataset

Results

The classification performance of MLP for different activations over Cars Evaluation, Iris and MNIST datasets.

Dataset	Activation Function	Training		Validation
		Loss	Accuracy	Loss	Accuracy
Car Eval.	Tanh	0.0341	98.84	0.0989	96.40
	Sigmoid	0.0253	98.77	0.1110	96.24
	ReLU	0.0285	99.10	0.0769	97.40
	Swish	0.0270	99.13	0.0790	97.11
	LiSHT	0.0250	99.28	0.0663	97.98
Iris	Tanh	0.0937	97.46	0.0898	96.26
	Sigmoid	0.0951	97.83	0.0913	96.23
	ReLU	0.0983	98.33	0.0886	96.41
	Swish	0.0953	98.50	0.0994	96.34
	LiSHT	0.0926	98.67	0.0862	97.33
	Tanh	1.1534	58.86	1.3759	51.74
	Sigmoid	1.1319	59.51	1.3693	52.12
	ReLU	1.1776	57.49	1.3731	51.85
	Swish	1.1468	58.65	1.3705	51.83
	LiSTh	1.1216	59.13	1.3661	52.16
MNIST	Tanh	0.0138	99.56	0.0987	98.26
	Sigmoid	0.0064	99.60	0.0928	98.43
	ReLU	0.0192	99.51	0.1040	98.48
	Swish	0.0159	99.58	0.1048	98.45
	LiSHT	0.0127	99.68	0.0915	98.60

The classification performance of ResNet for different activations over MNIST and CIFAR-10/100 datasets.

Dataset	ResNet Depth	Activation Functions
		Tanh	ReLU	Swish	LiSHT
MNIST	20	99.48	99.56	99.53	99.59
CIFAR-10	164	89.74	91.15	91.60	92.92
CIFAR-100	164	68.80	72.84	74.45	75.32

The classification performance of LSTM for different activations over twitter140 dataset.

Dataset	Activation Functions
	Tanh	ReLU	Swish	LiSHT
Twitter140	82.27	82.47	82.22	82.47

Citation

If you use this code or a derivative thereof in your research, we would appreciate a citation to the original paper:

@article{roy2019lisht,
        title={LiSHT: Non-Parametric Linearly Scaled Hyperbolic Tangent Activation Function for Neural Networks},
        author={Roy, Swalpa Kumar and Manna, Suvojit and Dubey, Shiv Ram and Chaudhuri, Bidyut B},
        journal={arXiv preprint arXiv:1901.05894},
        year={2019}
    }

License

The code is released under the MIT License. See the attached LICENSE file.