# Back-Propagation

Back-Propagation is a method used in **Artificial Neural Networks** during **Supervised Learning**. It is used to calculate the error contribution of each neuron after a batch of data. This popular algorithm is used to train multi-layer neural networks and is the backbone of many machine learning models.

{% embed url="https://youtu.be/YVy8BxN3nBI?si=VTiQBBD5kbjjgyvN" %}

## Back-Propagation: Introduction

| Domains          | Learning Methods | Type                      |
| ---------------- | ---------------- | ------------------------- |
| Machine Learning | Supervised       | Artificial Neural Network |

Back-Propagation is a widely used learning algorithm in the field of Artificial Neural Networks. It is a type of supervised learning method that allows for the calculation of the error contribution of each neuron after a batch of data is processed. This algorithm has proven to be highly effective in training neural networks to recognize patterns and make predictions.

## Back-Propagation: Use Cases & Examples

Back-Propagation is a popular method used in artificial neural networks, specifically in the training process, to calculate the error contribution of each neuron after a batch of data. This algorithm is commonly used in supervised learning, where the neural network is trained on a dataset with labeled examples.

One use case of Back-Propagation is in image classification. The neural network is trained on a dataset of images with corresponding labels. During the training process, the weights of the network are adjusted using Back- Propagation to minimize the error between the predicted labels and the true labels. Once the network is trained, it can be used to classify new images with high accuracy.

Another example of Back-Propagation is in natural language processing. In this use case, the neural network is trained on a dataset of text with corresponding labels, such as sentiment analysis or part-of-speech tagging. The Back-Propagation algorithm is used to adjust the weights of the network to minimize the error between the predicted labels and the true labels. Once the network is trained, it can be used to analyze new text data.

Back-Propagation is also used in speech recognition. The neural network is trained on a dataset of audio recordings with corresponding labels, such as transcriptions of the spoken words. The Back-Propagation algorithm is used to adjust the weights of the network to minimize the error between the predicted transcriptions and the true transcriptions. Once the network is trained, it can be used to transcribe new audio recordings with high accuracy.

Lastly, Back-Propagation is used in recommendation systems. The neural network is trained on a dataset of user behavior, such as past purchases or clicks, and corresponding labels, such as recommended products or articles. The Back- Propagation algorithm is used to adjust the weights of the network to minimize the error between the predicted recommendations and the true recommendations. Once the network is trained, it can be used to make personalized recommendations to users.

## Getting Started

Back-Propagation is a method used in artificial neural networks to calculate the error contribution of each neuron after a batch of data. It is a type of supervised learning method.

To get started with Back-Propagation, you will need to have a basic understanding of artificial neural networks and how they work. Once you have that, you can start implementing Back-Propagation in your code.

```
import numpy as np
import torch
from sklearn.datasets import make_classification
from sklearn.model_selection import train_test_split

# Generate some random data for classification
X, y = make_classification(n_samples=1000, n_features=10, n_classes=2)

# Split the data into training and testing sets
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2)

# Convert the data to PyTorch tensors
X_train = torch.from_numpy(X_train).float()
X_test = torch.from_numpy(X_test).float()
y_train = torch.from_numpy(y_train).float()
y_test = torch.from_numpy(y_test).float()

# Define the neural network architecture
class NeuralNet(torch.nn.Module):
    def __init__(self):
        super(NeuralNet, self).__init__()
        self.layer1 = torch.nn.Linear(10, 5)
        self.layer2 = torch.nn.Linear(5, 1)
        self.sigmoid = torch.nn.Sigmoid()

    def forward(self, x):
        x = self.layer1(x)
        x = self.sigmoid(x)
        x = self.layer2(x)
        x = self.sigmoid(x)
        return x

# Initialize the neural network
model = NeuralNet()

# Define the loss function and optimizer
criterion = torch.nn.BCELoss()
optimizer = torch.optim.SGD(model.parameters(), lr=0.01)

# Train the neural network
for epoch in range(100):
    # Forward pass
    y_pred = model(X_train)
    loss = criterion(y_pred, y_train)

    # Backward pass and optimization
    optimizer.zero_grad()
    loss.backward()
    optimizer.step()

    # Print the loss every 10 epochs
    if (epoch+1) % 10 == 0:
        print(f'Epoch [{epoch+1}/100], Loss: {loss.item():.4f}')

# Test the neural network
with torch.no_grad():
    y_pred = model(X_test)
    y_pred = np.round(y_pred.numpy())
    accuracy = (y_pred == y_test.numpy()).mean()
    print(f'Test Accuracy: {accuracy:.2f}')

```

## FAQs

### What is Back-Propagation?

Back-Propagation is a method used in artificial neural networks to calculate the error contribution of each neuron after a batch of data. It is a supervised learning method.

### How does Back-Propagation work?

The Back-Propagation algorithm works by calculating the gradient of the loss function with respect to each weight by application of the chain rule. This gradient is then used to update the weights in the network, with the goal of minimizing the loss function.

### What are the advantages of using Back-Propagation?

Back-Propagation is widely used because it is a very effective algorithm for training artificial neural networks. It is a relatively simple algorithm to implement, and can be used to train networks with many layers.

### What are the limitations of Back-Propagation?

Back-Propagation has several limitations. One limitation is that it can be slow to converge when used with large data sets. Another limitation is that it can get stuck in local minima, which can be a problem when training deep neural networks.

### How is Back-Propagation used in practice?

Back-Propagation is used in a wide variety of applications, including image and speech recognition, natural language processing, and robotics. It is an important tool for any machine learning engineer working with artificial neural networks.

## Back-Propagation: ELI5

Back-Propagation is like a teacher grading a student's homework. The teacher looks at each question in the homework and calculates how much the student got right or wrong. The teacher does this for every question, and then calculates the total score for the homework.

In artificial neural networks, Back-Propagation does something similar. It looks at each neuron in the network and calculates how much it contributed to the error in the network's output. Back-Propagation does this for every neuron, and then adjusts the weights of the connections between neurons to reduce the overall error in the output.

Think of Back-Propagation like a chef tasting a dish and adjusting the seasoning. Just as a chef tastes a dish, identifies what is missing, and then adds seasoning to make it taste better, Back-Propagation looks at the output of the neural network, identifies where it is incorrect, and then adjusts the weights of the connections between neurons to make it more accurate.

Another way to think of Back-Propagation is like a detective solving a crime. The detective looks at all the evidence, identifies where the crime was committed, and then uses that information to find the culprit. Similarly, Back-Propagation looks at all the neurons in the network, identifies where the error is being introduced, and then adjusts the weights of the connections between neurons to solve the problem.

In short, Back-Propagation is an algorithm used in artificial neural networks to identify and correct errors in the network's output. It is like a teacher grading homework, a chef adjusting seasoning, or a detective solving a crime. [Back Propagation](https://serp.ai/back-propagation/)
