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Subspace Clustering

Subspace Clustering. Ali Sekmen Computer Science College of Engineering Tennessee State University. 1 st Annual Workshop on Data Sciences. Outline. Subspace Segmentation Problem Motion Segmentation Principal Component Analysis Dimensionality Reduction Spectral Clustering Presenter

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Subspace Clustering

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  1. Subspace Clustering Ali Sekmen Computer Science College of Engineering Tennessee State University 1st Annual Workshop on Data Sciences

  2. Outline • Subspace Segmentation Problem • Motion Segmentation • Principal Component Analysis • Dimensionality Reduction • Spectral Clustering • Presenter • Dr. Ali Sekmen

  3. Subspace Segmentation • In many engineering and mathematics applications, data lives in a union of low dimensional subspaces • Motion segmentation • Facial images of a person with the same expression under different illumination approximately lie on the same subspace

  4. Face Recognition

  5. Problem Statement

  6. Problem Statement

  7. Problem Statement

  8. What are we trying to solve?

  9. Example – Motion Segmentation

  10. Motion Segmentation Motion segmentation problem can simply be defined as identifying independently moving rigid objects in a video.

  11. Motion Segmentation We will show that all trajectories lie in a 4-dim subspace of

  12. Motion Segmentation Z Z p z x Y Y X y X

  13. Motion Segmentation Z p z x Y X y

  14. Motion Segmentation Z p z x Y X y

  15. Motion Segmentation

  16. Motion Segmentation Y X

  17. Motion Segmentation Motion Segmentation Y X

  18. Motion Segmentation

  19. Motion Segmentation

  20. Principal Component Analysis • The goal is to reduce dimension of dataset with minimal loss of information • We project a feature space onto a smaller subspace that represent data well • Search for a subspace which maximizes the variance of projected points • This is equivalent to linear least square fitting • Minimize the sum of squared distances between points and subspace • We find directions (components) that maximizes variance in dataset • PCA can be done by • Eigenvalue decomposition of a data covariance matrix • Or SVD of a data matrix

  21. Least Square Approximation

  22. Principal Component Analysis

  23. Principal Component Analysis

  24. PCA with SVD Coordinates w.r.t. new basis

  25. Principal Component Analysis inch cm

  26. Principal Component Analysis

  27. Solution with SVD

  28. PCA: Pre-Processing

  29. PCA: Optimization

  30. PCA: Reduce Dimensionality

  31. PCA: Reduce Dimensionality

  32. General PCA

  33. Spectral Clustering • A very powerful clustering algorithm • Easy to implement • Outperforms traditional clustering algorithms • Example: k-means • It is not easy to understand why it works • Given a set of data points and some similarity measure between all pairs of data points, we divide data into groups • Points in the same group are similar • Points in different groups are dissimilar

  34. Spectral Clustering • Most of subspace clustering algorithms employ spectral clustering as the last step

  35. Similarity

  36. Spectral Clustering

  37. Spectral Clustering

  38. Spectral Clustering

  39. Spectral Clustering Example From Lecture Notes of Ulrike von Luxburg

  40. Spectral Clustering Example From Lecture Notes of Ulrike von Luxburg

  41. Spectral Clustering Example From Lecture Notes of Ulrike von Luxburg

  42. Spectral Clustering Example From Lecture Notes of Ulrike von Luxburg

  43. Spectral Clustering Example From Lecture Notes of Ulrike von Luxburg

  44. Spectral Clustering Example

  45. Spectral Clustering Example

  46. Spectral Clustering Example

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