GAAF-Keras

This is a Keras implementation of "Gradient Acceleration in Activation Functions (GAAF)". This repository includes ResNet_v1 and ResNet_v2 implementation to test and compare GAAF with original activation functions.

Gradient Acceleration in Activation Functions

"Gradient Acceleration in Activation Functions" proposes a new technique for activations functions, gradient acceeration in activation function (GAAF), that accelerates gradients to flow even in the saturation area. Then, input to the activation function can climb onto the saturation area which makes the network more robust because the model converges on a flat region.

GAAF

Experimental Results in the Paper

Prerequisites

• Python 3.x
• Keras (Tensorflow backend)

Prepare Data set

This repository use Cifar10 dataset. When you run the training script, the dataset will be automatically downloaded.

Change Activation Function

This repository supports two GAAF: GAAF_relu and GAAF_tanh. For the GAAF_relu, It uses shifted sigmoid function as shape function and you can set the shift parameter. For the GAAF_tanh, It uses modified Gaussian function with a peak point at y=1.

To change activation function, you can set activation on main.py with GAAF_relu, GAAF_tanh, and relu.

Supportive CNN Models

You can train and test with base CNN model listed below.

• ResNet_v1 (e.g. ResNet20, ResNet32, ResNet44, ResNet56, ResNet110, ResNet164, ResNet1001)
• ResNet_v2 (e.g. ResNet20, ResNet56, ResNet110, ResNet164, ResNet1001)

Train a Model

You can simply train a model with main.py.

1. Set depth for ResNet model
   • e.g. depth=20
2. Define a model you want to train.
   • e.g. model = resnet_v1.resnet_v1(input_shape=input_shape, depth=depth, activation=activation)
3. Set other parameter such as batch_size, epochs, data_augmentation and so on.
4. Run the main.py file
   • e.g. python main.py

Test Results

I conducted some experiments on ResNet20_v1 by replacing the original activation (relu) with GAAF_relu and the results is described as below.

num	data	backbone	activation	shift	steps	acc	batch_size	optimizer	lr
baseline	cifar10	resnet20_v1	relu	-	200	0.8084	128	adam	0.001
ex1	cifar10	resnet20_v1	GAAF_relu	5	200	0.6517	128	adam	0.001
ex2	cifar10	resnet20_v1	GAAF_relu	4	200	0.6924	128	adam	0.001
ex3	cifar10	resnet20_v1	GAAF_relu	3	200	0.7042	128	adam	0.001
ex4	cifar10	resnet20_v1	GAAF_relu	2	200	0.7441	128	adam	0.001
ex5	cifar10	resnet20_v1	GAAF_relu	1	200	0.78	128	adam	0.001
ex6	cifar10	resnet20_v1	GAAF_relu	0	200	0.7886	128	adam	0.001
ex7	cifar10	resnet20_v1	GAAF_relu	-0.5	200	0.7945	128	adam	0.001
ex8	cifar10	resnet20_v1	GAAF_relu	-1	200	0.7948	128	adam	0.001
ex9	cifar10	resnet20_v1	GAAF_relu	-2	200	0.78	128	adam	0.001
ex10	cifar10	resnet20_v1	GAAF_relu	-3	200	0.7768	128	adam	0.001
ex11	cifar10	resnet20_v1	GAAF_relu	-4	200	0.7733	128	adam	0.001
ex12	cifar10	resnet20_v1	GAAF_relu	no s(x)	200	0.6603	128	adam	0.001
ex13	cifar10	resnet20_v1	GAAF_relu(K.round)	-1	200	0.8054	128	adam	0.001

GAAF_relu actually did not give any improvement for every experiments. At the beginning of the experiment, I thought shift=4 will give the best performance as shifted sigmoid shape is very similar with the shape function that GAAF paper suggested. However, shift=-1 gives the best performance but still lower than the baseline. Interesting thing is, when I changed mut-tf.floor(mut) with K.abs(mut-K.round(mut)), it gives the best performance but less than the baseline. (Keras backend function does not have floor operation, so I attempted to use K.round)

If there is any implementation error in this repository, please let me know.

Related Works

• Blog: Gradient Acceleration in Activation Functions
• Repository: CBAM-keras

Reference

• Paper: Gradient Acceleration in Activation Functions
• Repository: Cifar10 ResNet example in Keras

Author

Byung Soo Ko / kobiso62@gmail.com