What is Activation Function?

  • Editor
  • February 1, 2024

What is an activation function? an activation function is a mathematical equation applied to a neuron in a neural network that determines whether it should be activated or not.

This function decides how to transform the input received into an output signal that is sent to the next layer of neurons. Essentially, activation functions introduce non-linearity into the network, enabling it to learn complex patterns and perform tasks beyond simple linear operations.

The activation function, a fundamental mechanism that dictates the output of neurons within a neural network, lies at the core of every neural network.

To learn more about activation functions and their significance in AI, read this article by the AI mentors at All About AI.

What is Activation Function?: The Secret Sauce Behind Smart Brains

Imagine your brain as a big network of tiny lights, where each light is a neuron. Now, think of an activation function like a switch for each light. This switch decides whether a light turns on or off based on a simple math problem. If the answer to the problem is “yes, turn on,” the light turns on. If it’s “no, don’t turn on,” the light stays off. So, in a way, the activation function is like a rule for each light, telling it when to shine and when to stay dark.

What is an Activation Function? Common Types of Activation Functions

Understanding the various types of activation functions is essential for designing and implementing neural networks effectively.


Linear Activation Function:

A straightforward function that maintains the input’s proportionality. However, it’s less commonly used due to its simplicity and inability to model complex patterns.

Sigmoid Activation Function:

Traditionally popular for its smooth gradient, though it has fallen out of favor due to issues like vanishing gradients.

ReLU (Rectified Linear Unit):

Currently, the most used activation function is known for its efficiency and simplicity in promoting faster convergence.

Tanh (Hyperbolic Tangent):

Similar to sigmoid but with outputs ranging from -1 to 1, making it better for certain types of data normalization.


Primarily used in the output layer for multi-class classification problems, converting logits to probabilities.

The Role of Activation Functions in Neural Networks

Activation functions are the lifeline of neural networks, enabling them to capture and model complex and non-linear functions.

  • Driving Non-Linearity: Their ability to introduce non-linearity is vital for modeling intricate patterns in datasets, a cornerstone in deep learning.
  • Guiding Network Architecture: The selection of an activation function can influence the architecture’s depth and learning capacity.
  • Optimizing Learning Dynamics: Choosing the right function affects learning speed and the backpropagation process, critical for model accuracy and efficiency.

Activation Functions in Deep Learning

Activation functions are fundamental elements within the algorithm of artificial intelligence, particularly in the structure and functionality of neural networks. These functions serve as gatekeepers, determining the output of a neural network layer’s neuron based on the input it receives.

This decision-making process is crucial for a neural network’s ability to process information and learn from data. By introducing non-linearity, activation functions allow neural networks to tackle complex problems that go beyond the capabilities of simple linear models.


Core Functions and Their Impact

Here are some of the crucial roles these functions play in neural networks, driving the transformative capabilities of AI systems. functions of activation.

Neural Network and Activation Functions:

At the heart of every neural network, from simple architectures to complex deep learning models, lies the activation function.

It’s what enables the network to capture and model complex patterns and relationships within data, facilitating tasks like image recognition, natural language processing, and predictive analytics.

Sigmoid Function:

Historically, the sigmoid function has been a popular choice for activation due to its smooth gradient and output range between 0 and 1, making it particularly useful for models where outputs are interpreted as probabilities, such as in binary classification tasks.

ReLU Function:

The Rectified Linear Unit (ReLU) function has gained prominence for its simplicity and effectiveness, especially in deep learning. By outputting zero for all negative inputs and maintaining positive inputs as is, the ReLU function introduces non-linearity while mitigating the vanishing gradient problem, thus enhancing computational efficiency and allowing models to learn faster and deeper.

Tanh Function:

The hyperbolic tangent (tanh) function, similar to the sigmoid but with an output range from -1 to 1, offers a centered scaling that can be advantageous in certain neural network layers, improving the model’s convergence over iterations.

Neuron Activation:

The activation function’s role extends beyond just a simple filter; it activates certain neurons within the network based on the relevance and importance of the incoming information, thereby directing the neural network’s focus and learning process.

Classification Tasks:

Activation functions are pivotal in classification tasks within artificial intelligence. For binary classification, functions like sigmoid are essential for determining the likelihood of inputs belonging to one class or another.

In multiclass classification, softmax functions extend this concept to multiple classes, assigning probabilities to each class and thus enabling the model to classify inputs into more than two categories.

Enhancing Computational Efficiency

The choice of activation function significantly influences a neural network’s training efficiency and its ability to generalize from training Big data. Functions like the ReLU have revolutionized deep learning by reducing the computational burden and enabling the training of very deep networks, which was previously challenging due to the computational cost and the vanishing gradient issue.

Understanding what is an activation function is crucial for anyone venturing into AI and neural network design. These functions are not just mathematical tools but are pivotal in shaping the learning capabilities and efficiency of AI models.

Choosing the Right Activation Function

The success of a neural network model heavily relies on the appropriate choice of activation function. This decision can significantly affect the model’s learning ability, performance, and computational efficiency.

Here are key points to consider when selecting an activation function for your neural network:


Assessing Model Needs:

The choice of an activation function should be tailored to the model’s specific requirements. This includes considering the nature of the input data, the complexity of the problem being solved, and the type of task, such as binary classification or multiclass classification. For instance, sigmoid functions might be preferred for binary outcomes, whereas softmax functions are better suited for multiclass scenarios.

Empirical Testing and Research:

Often, the selection process involves empirical testing to compare the performance of different activation functions within the same model architecture. This hands-on approach, coupled with staying informed about the latest advancements and findings in deep learning research, can guide you toward the optimal choice for your specific application.

Understanding Network Dynamics:

Different activation functions can influence the learning dynamics of a neural network in various ways. Functions like the ReLU function are known for enabling faster convergence in deep networks, while sigmoid and tanh functions might be more prone to issues like vanishing gradients in very deep architectures.

Computational Efficiency:

The computational cost of an activation function is another critical consideration, especially for models that require real-time processing or are trained on the very large database. Functions that are computationally simple and efficient, such as ReLU and its variants, can significantly reduce training times and resource consumption.

Avoiding Common Pitfalls:

Being aware of common issues associated with certain activation functions, such as the dying ReLU problem, where neurons permanently deactivate, can help in making a more informed choice. Exploring newer variants of traditional functions, like Leaky ReLU or ELU (Exponential Linear Unit), might offer improved performance and stability.

Compatibility with Model Architecture:

Some activation functions are more compatible with specific neural network architectures or layers. For example, softmax is typically used in the output layer for classification tasks, while ReLU and its variants are often preferred in hidden layers of deep networks.

Theoretical Backing:

Lastly, understanding the theoretical aspects and the intuition behind different activation functions can provide deeper insights into how they might affect the network’s ability to model complex relationships and generalize from training data.

Want to Read More? Explore These AI Glossaries!

AI Glossary Handbook: Ideal for beginners and advanced AI aficionados alike, our comprehensive glossaries provide an easy-to-understand resource. Explore the detailed facets and innovative breakthroughs in AI, positioning this handbook as your indispensable companion for navigating the complexities of this field.

  • What is Similarity learning?: It is a concept at the heart of many artificial intelligence (AI) and machine learning systems, and revolves around the idea of identifying how alike or different data points are.
  • What is Simulated Annealing (SA)?: It is an advanced probabilistic technique used for finding an approximate global optimum of a given function.
  • What is Singularity?: Simply put, it refers to a hypothetical future point where technological growth becomes uncontrollable and irreversible, resulting in unfathomable changes to human civilization.
  • What is a Situated Approach?: It represents a paradigm shift from traditional AI methods. It emphasizes the importance of AI systems interacting dynamically with their environment, rather than operating in isolation.
  • What is Situation Calculus?: It’s a framework used for modeling dynamic domains, providing a way to describe how the state of the world changes in response to actions.


It’s the rule that helps a neural network decide what information should pass through, acting as a gatekeeper for neuron activation.

The ReLU function is widely favored for its simplicity and effectiveness in combating the vanishing gradient dilemma, enhancing deep learning models.

It becomes akin to a linear model, incapable of understanding the complex, non-linear functions present in real-world data.

Activation functions control the output of neurons, while loss functions measure the accuracy of the model during training, guiding backpropagation.

Wrap Up

This article was written to answer the question “What is an activation” function, which is the heartbeat of neural network technology. These functions empower neural networks to decipher complex datasets, making strides in binary classification, multiclass classification, and beyond.

The choice of activation function—be it Sigmoid function, ReLU function, or Tanh function—significantly influences a model’s learning capabilities and computational efficiency. This exploration not only highlights the indispensable role of activation functions in deep learning but also encourages ongoing advancements in the field.

For further insights into neural network technologies and strategies, our extensive AI terminology page awaits your curiosity.

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Dave Andre


Digital marketing enthusiast by day, nature wanderer by dusk. Dave Andre blends two decades of AI and SaaS expertise into impactful strategies for SMEs. His weekends? Lost in books on tech trends and rejuvenating on scenic trails.

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