Introduction to Deep Learning and Neural Networks

Introduction to Deep Learning and Neural Networks

1. Introduction to Deep Learning and Neural Networks

Deep Learning involves the training of Neural Networks, often encompassing very large and complex structures. At its core, a Neural Network is designed to simulate the way human brains operate, allowing machines to solve problems in ways that mimic human thought processes.

2. Understanding Neural Networks Through a Housing Price Prediction Example

2.1 Linear Regression and Its Limitations

A foundational approach to predicting housing prices involves linear regression, where a straight line is fitted to data points representing house sizes and their corresponding prices. However, this method's limitation becomes apparent as it can predict negative prices, which are practically impossible.

2.2 Introduction to the ReLU Function

To overcome the limitations of linear regression, the Rectified Linear Unit (ReLU) function is introduced. This function ensures that the output is zero for negative input values, addressing the issue of impossible negative predictions in our housing price example.

3. Building Blocks of Neural Networks: Neurons and Layers

3.1 The Single Neuron: The Basic Unit of Neural Networks

A single neuron can be visualized as a node that takes in an input, processes it through a function (like ReLU), and outputs a prediction. This is the simplest form of a neural network.

3.2 Stacking Neurons: From Single Neurons to Layers

Larger neural networks are built by stacking these single neurons together. This is similar to connecting multiple Lego bricks to form complex structures, allowing for the processing of more detailed and nuanced information.

Wait WHAT? Neurons? Linear Regression?

3.3 What is the connection?

It's a common question and a great topic of observation! Neural Networks and Linear Regression might seem quite different at first glance; one is a foundational statistical method, and the other is a complex model inspired by the human brain. However, they are more closely related than they might appear, especially in terms of the foundational concepts they are built upon. Let's break down how they are connected:

4. Linear Regression Basics

4.1 Linear Regression

  • Linear Regression is one of the simplest forms of predictive modelling techniques. It assumes a linear relationship between the input variables (X) and the single output variable (y). When you have one input variable, it's called simple linear regression; for more than one, it's called multiple linear regression.

  • The goal in linear regression is to find the best-fitting line (in 2D) or hyperplane (in higher dimensions) that predicts the output variable.

4.2 Neural Networks Basics

  • Neural Networks, on the other hand, consist of layers of neurons, with the simplest form being a single-layer perceptron. They can model complex nonlinear relationships between inputs and outputs by adjusting weights and biases through a process called backpropagation.

4.3 The Connection

  1. Linear Modeling as a Building Block: At their core, the neurons (or nodes) in neural networks perform a weighted sum of their inputs, which is a linear operation. This is fundamentally what happens in linear regression too. The difference is that in neural networks, this linear output can then be passed through a nonlinear activation function, like the ReLU function, to introduce non-linearity.

  2. Single-Layer Perceptron as Linear Regression: A single-layer neural network without any activation function (or with a linear activation function) is, mathematically, doing exactly what linear regression does. It's trying to find the weights (coefficients in linear regression terminology) that best map the inputs to the output. So, you can think of linear regression as a special case of neural networks.

  3. Complexity and Flexibility: While linear regression can only model linear relationships, neural networks can model both linear and nonlinear relationships. This is because neural networks can add layers and neurons and use different activation functions to capture the complexity of data.

  4. Nonlinear Activation Functions: The introduction of nonlinear activation functions is what allows neural networks to go far beyond what linear regression can model. This is how neural networks can learn complex patterns that linear models like regression cannot.

  5. From Simple to Complex: The progression from linear regression to neural networks can be seen as moving from understanding simple linear relationships to modelling complex and highly nonlinear dynamics. Each neuron in a neural network can be thought of as performing a linear regression-like operation on its inputs, but the collective operation across multiple layers and neurons allows for much more complex mappings.

While linear regression and neural networks can seem very different due to their applications and capabilities, the basic operation at the heart of a neuron in a neural network has similarities with linear regression. This foundational connection is what makes it easier for people familiar with linear regression to grasp the initial concepts of neural networks. As you add more layers and non-linearity, neural networks become capable of capturing complex patterns far beyond the scope of linear regression, yet the starting point shares a conceptual link.

5. Expanding the Neural Network: Incorporating Multiple Features

5.1 Predicting with Multiple Inputs

A more sophisticated neural network can take multiple features into account (e.g., house size, number of bedrooms, zip code, neighbourhood wealth) to make more accurate predictions regarding housing prices.

5.2 The Architecture of a Multi-Feature Neural Network

In this expanded network, each feature is connected to multiple neurons, each potentially representing different aspects of the housing market (e.g., family size, walkability, school quality). This structure allows the neural network to make comprehensive predictions based on a wide array of inputs.

6. The Power of Neural Networks in Supervised Learning

6.1 Training Neural Networks with Data

Neural networks learn to make predictions by being trained on a dataset that includes both the input features (X) and the output (Y). The network learns the optimal way to map inputs to outputs through this training process.

6.2 Neural Networks’ Ability to Map Inputs to Outputs

One of the most remarkable aspects of neural networks is their ability to discover the underlying function that accurately maps inputs to outputs, given enough training data. This makes them extremely powerful tools for supervised learning tasks.

7. Conclusion and Look Forward

We've explored the basics of neural networks and their applications in predicting housing prices. As we delve deeper into deep learning, we'll discover even more applications and the incredible potential of neural networks in solving complex problems.

This blog serves as an introduction to the fundamental concepts of neural networks and deep learning, setting the stage for more advanced discussions on this transformative technology.


Source of information:
DeepLearning.AI: Start or Advance Your Career in AI