spectral clustering

Data
spectral clustering algorithm

  1. Diagonalize A=VΛVT
  2. Order the eigenvectors by decreasing eigenvalue magnitude
    This yields $$V_{c} = \begin{bmatrix}v_{1} & v_{2} & \dots & v_{c}\end{bmatrix}, v_{i} \in \mathbb{R}^n = \begin{bmatrix}u_{1} \
    u_{2} \
    \vdots \
    u_{n}
    \end{bmatrix}, u_{j} \in \mathbb{R}^c$$
    we can see the rows uj as embeddings of the notes in Rc (community space)
  3. yay we can cluster (k-means or whatever you want. can also use like gaussian mixture models)

This is the unsupervised version of spectral embedding.

See also graph fourier transform

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spectral embedding
2025-02-10 graphs lecture 6
2025-02-12 graphs lecture 7