A Beginner’s Guide to Neural Networks
Tags: beginners, ai, machinelearning, programming
Published: 2023-12-22 16:21:35

Neural networks, a fascinating blend of computer science and mathematics, mimic the workings of the human brain to solve complex problems that were once considered impossible for machines. 

Their ability to learn from vast amounts of data and recognize patterns sets them apart as a revolutionary force in artificial intelligence.

Neural networks are at the heart of numerous technological breakthroughs in recent years, powering everything from sophisticated image recognition to advanced natural language processing systems.

If you’ve followed our journey through [the emergence of autonomous agents](https://apidna.io/the-emergence-of-autonomous-agents/), you’ll find neural networks to be the critical technology enabling these agents to utilise [machine learning](https://apidna.io/simplifying-the-fundamentals-of-machine-learning/) and make decisions.

This guide will introduce you to the basic concepts of neural networks, illustrating their importance in shaping the future of tech.

## What Are Neural Networks?

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ft788r8abnxzsm9et4sd.jpg)

At their core, neural networks are a series of algorithms designed to recognize patterns, interpreting sensory data through a kind of machine perception, labelling, or clustering of raw input. 

They are structured in a way that mimics the human brain’s connections of neurons, hence the name ‘neural networks’. 

Just like neurons in the brain that transmit and process information, each ‘neuron’ in a neural network takes in data, processes it, and passes it on.

Imagine each neuron in a neural network as a switch that gets turned on or off based on the input it receives, much like how a light switch works. 

When these switches are connected in a vast network, they work together to solve complex problems, from identifying patterns to making decisions. 

This connectivity and processing ability make neural networks incredibly powerful in various applications.

Neural networks are widely used in numerous fields. 

In image recognition, they analyse visual data, identifying and classifying objects as accurately as, or even more accurately than, humans. 

In natural language processing, they understand and interpret human language, enabling technologies like voice assistants and language translation services. 

From self-driving cars to medical diagnosis, neural networks are revolutionising industries by providing deeper insights and more efficient solutions to complex problems.

## How Do Neural Networks Work?

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/n7h696h9c58sxnlwa5lk.jpg)

Their basic structure consists of layers of neurons connected in a network. 

Each neuron in these layers serves as a fundamental processing unit, working together to process input data and produce an output.

A neural network typically consists of three types of layers: the input layer, one or more hidden layers, and the output layer. 

The input layer receives the raw data, which is then processed through successive hidden layers and finally passed to the output layer. 

The magic of neural networks happens primarily in these hidden layers.

Let’s break down these layers further:

1. **Input Layer:** This is where the neural network receives its input data. Each neuron in this layer represents a unique piece of information from the input data, such as a pixel in an image or a word in a sentence.
2. **Hidden Layers:** Hidden layers lie between the input and output layers. Each neuron in these layers performs computations using weights and biases – these are parameters that the network learns during training. The neurons in these layers are interconnected, and each connection carries a weight. When data passes through a neuron, it is multiplied by these weights and offset by a bias, allowing the network to learn complex patterns and relationships in the data.
3. **Output Layer:** The final layer in a neural network, the output layer, produces the final results. For example, in a classification task, this could be the probabilities of the input belonging to various classes.

Imagine a simple neural network used for recognizing images of handwritten numbers. 

The input layer receives the pixel values of the image. 

These values are then passed through one or more hidden layers, where the network begins to recognize patterns and features, like edges or shapes. 

Finally, the output layer classifies the image as a digit between 0 and 9 based on the patterns recognized by the hidden layers.

Each neuron’s output is determined by an activation function, which decides whether the neuron should be activated or not. 

This function adds non-linearity to the network, enabling it to learn more complex patterns.

## Training a Neural Network

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/pxvptubpvvg4cri94w4r.jpg)

Training a neural network is like teaching it how to make accurate predictions or decisions based on input data. 

This training process hinges on two key elements: training data and labels.

Training data is a dataset used to train the neural network. 

It consists of numerous examples, each paired with a label. 

For instance, in image recognition, each image (the input) would have a corresponding label identifying what it depicts. 

These labels are crucial as they provide the ground truth that the network aims to predict.

The heart of a neural network’s learning ability lies in its weights and biases. 

Weights are parameters that determine the strength of the connection between neurons in different layers, while biases are additional parameters that allow each neuron to adjust its output. 

Initially, these weights and biases are set to random values and are gradually adjusted through training to minimise the difference between the network’s predictions and the actual labels.

Now that we have our training data, labels, weights and biases established, here is the four step process to train a neural network:

- **Forward Propagation:** The process begins with forward propagation, where input data is passed through the network, layer by layer, until it reaches the output layer. At each neuron, the incoming data is processed by multiplying it with the neuron’s weights, adding a bias, and applying an activation function. This produces the network’s prediction.
- **Activation Function:** The activation function in each neuron decides whether it should be activated (or how much it should contribute to the network’s output). Common activation functions include sigmoid, tanh, and ReLU (Rectified Linear Unit). These functions introduce non-linearity, enabling the network to learn complex patterns.
- **Backward Propagation (Backpropagation):** This is where the network learns from its errors. After forward propagation, the network assesses its performance by comparing its output with the actual labels, using a loss function. The loss function calculates the error, which is then propagated back through the network. This backward pass helps the network understand where it made errors and how to adjust its weights and biases to reduce these errors. The process of adjusting weights and biases is done through optimization algorithms like gradient descent.
- **Iterative Learning:** The forward and backward propagation processes are repeated over many iterations (or epochs) across the training data. With each iteration, the network fine-tunes its weights and biases to minimise the error, gradually learning to make more accurate predictions or decisions.

Training a neural network is a delicate balancing act – it requires sufficient iterations to learn effectively, but too many can lead to overfitting, where the network becomes too tailored to the training data and performs poorly on new, unseen data. 

This training process is crucial for the neural network to develop its predictive or decision-making abilities, making it a fundamental aspect of neural network implementation.

## Types of Neural Networks
Neural networks come in various architectures, each suited to specific types of problems and data. 

Understanding these different types of neural networks and their specific applications helps in choosing the right model for a given problem. 

Each type has its unique architecture and learning abilities, making them suitable for various tasks in the vast domain of artificial intelligence and machine learning.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/jk2n0jo46of58vmsivp8.jpg)

### Feedforward Neural Networks (FNNs)
In FNNs, the information moves in only one direction – forward – from the input nodes, through the hidden nodes (if any), and to the output nodes. 

There are no cycles or loops in the network.

FNNs are the simplest type of neural network architecture and are widely used for general purposes. 

They’re often employed in tasks like sales forecasting, customer research, and risk assessment.

### Convolutional Neural Networks (CNNs)
CNNs are designed to process data in the form of multiple arrays, such as a colour image composed of three 2D arrays containing pixel intensities in the RGB colour model. 

They include convolutional layers that apply a convolution operation to the input, passing the result to the next layer.

CNNs excel in processing visual data and are predominantly used in image recognition and processing tasks. 

They can identify faces, objects, and traffic signs, and are used in applications like self-driving cars and medical image analysis.

### Recurrent Neural Networks (RNNs)
RNNs have loops to allow information to persist. In an RNN, the output from one step is fed back as input for the next step. 

This structure makes them effectively ‘remember’ some of the information about what has been processed so far.

RNNs are used for sequential data like time series, speech, text, financial data, audio, video, weather, and more. 

They are fundamental in applications like language modelling and translation, speech recognition, and even in generating captions for images.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/v6hcxmpzpvwmjr3mrx2t.jpg)

### Long Short-Term Memory Networks (LSTMs)
A special kind of RNN, LSTMs are capable of learning long-term dependencies. 

They remember information for long periods as their default behaviour, addressing the limitation of traditional RNNs.

LSTMs are useful for a variety of sequence prediction problems, especially when the network needs to learn from important experiences that happened many steps back in the sequence. 

This makes them effective for complex tasks like predicting the next word in a sentence.

### Autoencoders
An autoencoder is a type of neural network used to learn efficient codings of unlabelled data. 

The network is trained to use its encoding layers to compress the input into a latent-space representation and then reconstruct the output from this representation through its decoding layers.

Autoencoders are primarily used for feature extraction, image reconstruction, and as a pre-processing step for more complex tasks like anomaly detection.

## Conclusion
Neural networks, with their unique ability to learn and adapt, are becoming integral in shaping advancements in areas like image recognition, natural language processing, and beyond. 

They are not just tools for experts but are increasingly accessible for enthusiasts and junior developers eager to explore the possibilities of AI.

As you move forward, remember that the field of neural networks is vast and continuously evolving. 

The journey of learning and experimentation never truly ends. 

With each project and experiment, you will gain a deeper understanding and appreciation for the capabilities of these incredible models.

## Further Reading
[Machine Learning for Beginners: An Introduction to Neural Networks](https://towardsdatascience.com/machine-learning-for-beginners-an-introduction-to-neural-networks-d49f22d238f9)

[A Beginner’s Guide to Important Topics in AI, Machine Learning, and Deep Learning](https://wiki.pathmind.com/neural-network)

[An Ultimate Tutorial to Neural Networks](https://www.simplilearn.com/tutorials/deep-learning-tutorial/neural-network)

[Beginners Guide to Artificial Neural Network](https://www.analyticsvidhya.com/blog/2021/05/beginners-guide-to-artificial-neural-network/)