# Unveiling the Role and Properties of the Sigmoid Activation Function

Have you ever wondered how neural networks make decisions? While the input data may paint a picture, it’s the activation function that provides the final verdict.

The activation function is a crucial component of artificial neural networks, as it determines the output of each individual neuron. In this article, we will explore the different types of activation functions, with a particular focus on the sigmoid activation function.

## Types of Activation Functions

There are several activation functions that play a role in the decision-making process of a neural network. One of the most popular is the ReLu (Rectified Linear Unit) function, which is a simple yet effective function that sets all negative output values to zero.

Another commonly used activation function is the Softmax function, which is useful for multi-class classification problems. The tanh (hyperbolic tangent) function is another type of activation function that is commonly used, as is the Linear function, which doesn’t perform any transformation on the input data.

Another popular activation function is the Leaky ReLu function, which aims to solve the issue of “dying ReLus,” where some ReLUs may become permanently inactive. The Leaky ReLu function remedies this by introducing a small slope for negative values.

However, in this article, we will focus on the sigmoid activation function.

## Sigmoid Activation Function

The sigmoid activation function is a type of activation function that is commonly used in artificial neural networks. Its name comes from the “S”-shaped curve that it produces when graphed.

The sigmoid function is useful for binary classification problems, where the output is either one value or another. The sigmoid function takes any input value and maps it onto a value between 0 and 1, allowing it to output a probability.

This probability determines the likelihood that a given input belongs to a certain class.

## Mathematically Representing Sigmoid Function using Equation

### The sigmoid function can be mathematically represented using the following equation:

(x) = 1 / (1 + e^(-x))

where x represents the input to the neuron, and (x) represents the output. If the input to the neuron is negative, then the output will be a value closer to 0.

If the input is positive, then the output will be closer to 1. The sigmoid function is useful because it allows us to mathematically represent the probability of a given output value.

For example, if the output value is 0.7, we can say that there is a 70% chance that the input belongs to class A.

## Derivation of the Relation between Sigmoid Equations

There is a relation between the sigmoid function and its derivative, which can be derived using calculus. The derivative of the sigmoid function with respect to x is given by:

‘(x) = (x) * (1 – (x))

This derivative is useful because it allows us to calculate the rate of change of the sigmoid function at any point.

If the rate of change is large, then the output value will change quickly. If the rate of change is small, then the output value will change slowly.

## Deriving the Derivative of Sigmoid Function

To derive the derivative of the sigmoid function, we start by taking the derivative of the equation for (x):

(x) = 1 / (1 + e^(-x))

‘(x) = (-1 / (1 + e^(-x))^2) * -e^(-x)

‘(x) = e^(-x) / (1 + e^(-x))^2

We can simplify this equation by multiplying the numerator and denominator of the fraction by e^x:

‘(x) = (e^(-x) * e^x) / (1 + e^(-x))^2

‘(x) = (1 / (1 + e^(-x))) * (e^x / (1 + e^(-x)))

We recognize the first term from the original sigmoid equation as (x):

‘(x) = (x) * (e^x / (1 + e^(-x)))

We can simplify this equation further by dividing the numerator and denominator of the fraction by e^x:

‘(x) = (x) * (1 / (1 + e^x))

Finally, we substitute the equation for (x) into this equation:

‘(x) = (x) * (1 – (x))

## Conclusion

In conclusion, the sigmoid activation function is a popular and useful type of activation function that is commonly used in neural networks. It allows us to calculate the probability of a given output value, making it useful for binary classification problems.

By understanding the mathematical representation of the sigmoid function and its derivative, we can gain insight into the inner workings of neural networks. While there are many types of activation functions, the sigmoid activation function remains a fundamental component of modern neural network architecture.

## 3) Understanding the Graph of Sigmoid Function

Now that we have discussed the mathematical representation and properties of the sigmoid function, let’s take a closer look at its graph. We can plot the graph of the sigmoid function using Python’s Matplotlib library.

## Plotting the Graph using Python Matplotlib

To plot the graph of the sigmoid function using Matplotlib, we first need to import the necessary libraries and create an array of input values. We can then apply the sigmoid function to this array and plot the output values against the input values.

Here’s an example Python code for plotting the sigmoid function:

``````import numpy as np
import matplotlib.pyplot as plt

def sigmoid(x):
return 1 / (1 + np.exp(-x))

x = np.linspace(-10, 10, 100)
y = sigmoid(x)

plt.plot(x, y)
plt.xlabel('x')
plt.ylabel('y')
plt.title('Sigmoid Function')
plt.show()
``````

In this example, we import the NumPy and Matplotlib libraries, define a sigmoid function that takes an input value x and returns the sigmoid output value, create an array of input values using the NumPy linspace function, apply the sigmoid function to this array, and finally plot the output values against the input values using Matplotlib. The resulting graph will be an S-shaped curve that ranges from 0 to 1 on the y-axis and from negative infinity to positive infinity on the x-axis.

## Identification and Explanation of Properties of Sigmoid Function

One of the key properties of the sigmoid function is its S-shaped curve. This curve indicates that the output value of the sigmoid function is continuous and monotonically increasing.

The sigmoid function also has a domain that ranges from negative infinity to positive infinity, meaning that it can accept any real number as its input. Another important property of the sigmoid function is its non-linearity.

The output of the sigmoid function is not a linear function of its input, meaning that small changes in the input value can result in large changes in the output value. The sigmoid function is also useful for binary classification problems because it maps the input value onto a value between 0 and 1, allowing it to output a probability.

If the output value is greater than or equal to 0.5, the input is classified as belonging to one class. If the output value is less than 0.5, the input is classified as belonging to another class.

## Relationship between Sigmoid and tanh Activation Functions

The sigmoid function and the tanh (hyperbolic tangent) function are both commonly used activation functions in neural networks. The tanh function is similar to the sigmoid function in that it maps the input value onto a value between -1 and 1.

However, the tanh function is centered around 0, meaning that its output values are both positive and negative. The tanh function also has steeper gradients than the sigmoid function, meaning that it allows for more efficient learning in the network.

However, the tanh function suffers from a problem called “vanishing gradients,” where the gradients become very small and learning slows down. Despite these differences, both the sigmoid and tanh functions are useful for neural network architectures and are commonly used in different types of layers within those architectures.

## 4) Summary

In summary, the sigmoid function is a widely used activation function in artificial neural networks. It is a non-linear function that maps the input value onto a value between 0 and 1, allowing for probabilistic output values.

The sigmoid function has several important properties, including its S-shaped curve, its continuous and monotonically increasing output, and its non-linear behavior. The sigmoid function is one of several activation functions used in neural networks, with others including the tanh function.

While there are differences between these functions, both the sigmoid and tanh functions remain fundamental components of modern neural network architecture. In conclusion, the sigmoid activation function is a crucial component of artificial neural networks that provides probabilistic output values for binary classification problems.

Its S-shaped curve, continuous output, and non-linear behavior make it useful for efficient learning in neural network architectures. Additionally, the sigmoid function is one of several activation functions used in neural networks, including the tanh function.

Understanding the properties and behavior of the sigmoid activation function can help improve the accuracy and performance of neural networks. As the field of artificial intelligence and machine learning continues to grow, knowledge of activation functions like the sigmoid function will remain critical for future advancements.