# Label Propagation Algorithm

Examples & Code

The Label Propagation Algorithm (LPA) is a **graph-based** semi-supervised machine learning algorithm that assigns labels to previously unlabeled data points. LPA works by propagating labels from a subset of data points that are initially labeled to the unlabeled points. This is done throughout the course of the algorithm, with the labels being kept fixed unlike the closely related algorithm, label spreading. LPA is commonly used in various applications such as community detection and image segmentation.

{% embed url="https://youtu.be/NZ_sLh4c-cM?si=cYAZpUkwWhcIBFvJ" %}

## Label Propagation Algorithm: Introduction

| Domains          | Learning Methods | Type        |
| ---------------- | ---------------- | ----------- |
| Machine Learning | Semi-Supervised  | Graph-based |

The Label Propagation Algorithm (LPA) is a graph-based semi-supervised machine learning algorithm that assigns labels to previously unlabeled data points. Unlike the closely related algorithm label spreading, LPA keeps the labels fixed at the start of the algorithm for a subset of the data points and propagates these labels to the unlabeled points throughout the course of the algorithm.

## Label Propagation Algorithm: Use Cases & Examples

The Label Propagation Algorithm (LPA) is a graph-based semi-supervised machine learning algorithm that assigns labels to previously unlabeled data points.

One use case of LPA is in community detection, where the algorithm can be used to identify communities or clusters within a graph. LPA can also be used in image segmentation to group pixels with similar properties, such as color or texture.

Another example of LPA is in recommendation systems, where the algorithm can be used to suggest products or services to users based on their past behavior and preferences. LPA can also be used in social network analysis to identify influential nodes or communities within a network.

Furthermore, LPA has been used in natural language processing to classify text documents based on their content. The algorithm can also be used in bioinformatics to identify functional modules in protein interaction networks.

## Getting Started

To get started with Label Propagation Algorithm (LPA), you will need to have a basic understanding of graph-based algorithms and semi-supervised learning. LPA is a semi-supervised machine learning algorithm that assigns labels to previously unlabeled data points. At the start of the algorithm, a subset of the data points have labels. These labels are propagated to the unlabeled points throughout the course of the algorithm. LPA keeps the labels fixed unlike the closely related algorithm label spreading.

Here is an example code using Python and the NumPy, PyTorch, and Scikit-learn libraries:

```
import numpy as np
from sklearn import datasets
from sklearn.semi_supervised import LabelPropagation
from sklearn.metrics import accuracy_score

# Load the iris dataset
iris = datasets.load_iris()

# Split the dataset into features and labels
X = iris.data
y = iris.target

# Set the first 10 labels as known
y_train = np.copy(y)
y_train[10:] = -1

# Create the LabelPropagation model
lp_model = LabelPropagation(kernel='knn', n_neighbors=10)

# Fit the model
lp_model.fit(X, y_train)

# Predict the labels of the remaining data points
y_pred = lp_model.predict(X)

# Calculate the accuracy score
accuracy = accuracy_score(y, y_pred)

print("Accuracy:", accuracy)

```

## FAQs

### Name: Label Propagation Algorithm

Abbreviation: LPA

Definition: Label propagation is a semi-supervised machine learning algorithm that assigns labels to previously unlabeled data points. At the start of the algorithm, a subset of the data points have labels. These labels are propagated to the unlabeled points throughout the course of the algorithm. LPA keeps the labels fixed unlike the closely related algorithm label spreading.

Type: Graph-based

Learning Methods:

* Semi-Supervised Learning

## Label Propagation Algorithm: ELI5

The Label Propagation Algorithm (LPA) is a fancy machinespectacular that can help computers give names to things. Think of it like a group of people trying to name a new puppy. At first, some people might suggest names they like, but not everyone will agree - just like how not all the data points have labels in LPA.

As the group talks more, they start to suggest names that are similar to each other, and over time, the group agrees on a name that fits the puppy's personality. In LPA, labeled data points are used as a starting point and the algorithm tries to find similar unlabeled points and give them a label too.

But how does LPA decide which labels to give to which data points? The algorithm takes into account the labels of neighboring data points, just like how the people in the group listen to each other's name suggestions to come to a consensus. With LPA, a data point's label is influenced by the labels of the other data points it's connected to. This way, the algorithm can propagate labels throughout the entire dataset.

LPA is a type of graph-based algorithm that falls under the category of semi- supervised machine learning. It's a powerful tool that can help make sense of large, complex datasets where not all the data points are labeled. [Label Propagation Algorithm](https://serp.ai/label-propagation-algorithm/)
