Efficient implementation of Tanh activation function and its Derivative (gradient) in Python

The mathematical definition of the Tanh activation function is

f(x)= \tanh(x)

and its derivative is defined as
f'(x)= 1-\tanh ^2(x)

The Tanh function and its derivative for a batch of inputs (a 2D array with nRows=nSamples and nColumns=nNodes) can be implemented in the following manner:
Tanh simplest implementation

import numpy as np
def Tanh(x):
    return np.tanh(x)

Tanh derivative simplest implementation

import numpy as np
def Tanh_grad(x):
    return 1.-np.tanh(x)**2 # sech^2{x}

However, these implementations can be further accelerated (sped-up) by using Numba (https://numba.pydata.org/). Numba is a Just-in-time (JIT) compiler that

translates a subset of Python and NumPy code into fast machine code.

To use numba, install it as:

pip install numba

Also, make sure that your numpy is compatible with Numba or not, although usually pip takes care of that. You can get the info here: https://pypi.org/project/numba/

Accelerating the above functions using Numba is quite simple. Just modify them in the following manner:

Tanh NUMBA implementation

from numba import njit 
@njit(cache=True,fastmath=True)
def Tanh(x):
    return np.tanh(x)

Tanh derivative NUMBA implementation

from numba import njit 
@njit(cache=True,fastmath=True)
def Tanh_grad(x):
    return 1.-np.tanh(x)**2 # sech^2{x}

This is quite fast and competitive with Tensorflow and PyTorch (https://github.com/manassharma07/crysx_nn/blob/main/benchmarks_tests/Performance_Activation_Functions_CPU.ipynb).

It is in fact also used in the CrysX-Neural Network library (crysx_nn)

Furthermore, the above implementations can be further accelerated using Cupy (CUDA), if using single precision (float32) is not a problem.

CuPy is an open-source array library for GPU-accelerated computing with Python. CuPy utilizes CUDA Toolkit libraries to make full use of the GPU architecture.

The Cupy implementations look as follows:

import cupy as cp     
def Tanh_cupy(x):
    return cp.tanh(x)
def Tanh_grad_cupy(x):
    return 1.-cp.tanh(x)**2 # sech^2{x}

The above code is also used in the crysx_nn library.
To see how the crysx_nn implementations of Tanh compare with TensorFlow and PyTorch, click here.

I hope you found this information useful.

If you did, then don’t forget to check out my other posts on Machine Learning and efficient implementations of activation/loss functions in Python.

PhD researcher at Friedrich-Schiller University Jena, Germany. I'm a physicist specializing in theoretical, computational and experimental condensed matter physics. I like to develop Physics related apps and softwares from time to time. Can code in most of the popular languages. Like to share my knowledge in Physics and applications using this Blog and a YouTube channel.
[wpedon id="7041" align="center"]

Leave a Reply

Your email address will not be published. Required fields are marked *