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Non-Negative Matrix Factorization (NMF) in Python

Non-Negative Matrix Factorization (NMF) is a dimensionality reduction technique used in machine learning and data analysis. It is a factorization technique that decomposes a high-dimensional matrix into two lower-dimensional matrices, with the constraint that all elements in the matrices are non-negative.

Purpose of NMF

The primary purpose of NMF is to identify patterns and features in high-dimensional data by reducing the dimensionality of the data while preserving the most important information. NMF is particularly useful in applications where the data is non-negative, such as:

  • Text analysis: NMF can be used to extract topics from a large corpus of text documents.
  • Image analysis: NMF can be used to extract features from images, such as object recognition.
  • Recommendation systems: NMF can be used to build recommendation systems based on user behavior.
  • Audio analysis: NMF can be used to extract features from audio signals.

How NMF Works

NMF works by decomposing a high-dimensional matrix V into two lower-dimensional matrices W and H, such that V ≈ WH. The matrices W and H are constrained to have non-negative elements, which ensures that the factorization is interpretable and meaningful.

The NMF algorithm iteratively updates the matrices W and H to minimize the difference between V and WH. The update rules are based on the following equations:


W = W * (V / (W * H)) / (W * (H / H))
H = H * (V / (W * H)) / (H * (W / W))

NMF in Python

Python provides several libraries that implement NMF, including scikit-learn and TensorFlow. The following example uses scikit-learn to perform NMF on a sample dataset:


import numpy as np
from sklearn.decomposition import NMF

# Create a sample dataset
V = np.array([[1, 0, 0, 1], [0, 1, 1, 0], [1, 1, 0, 1]])

# Create an NMF model with 2 components
model = NMF(n_components=2, init='random', random_state=0)

# Fit the model to the data
W = model.fit_transform(V)
H = model.components_

# Print the factorized matrices
print("W:")
print(W)
print("H:")
print(H)

This example demonstrates how to use NMF to decompose a high-dimensional matrix into two lower-dimensional matrices. The resulting matrices W and H can be used for further analysis, such as clustering or visualization.

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