A place to find a wealth of examples is in graph signal processing, where spectral decomposition of the Laplacian is known as the graph Fourier transform.
- A. Ortega, Introduction to Graph Signal Processing. Cambridge (2022), chapter 3 for the GFT and chapter 7 for examples.
Spectral graph theoretic examples are discussed in various places for example:
This finds applications in graph and convolution based machine learning, and neuroimaging/brain connectivity, and perhaps as a illustrative example on road traffic data.
There is also work in TDA and Applied Topology/Persistence along these lines such as persistent laplacians:
There are applications in protein engineering, covid variant forcasting and genomics.
- Wei, Xiaoqi, and Guo-Wei Wei. "Persistent Topological Laplacians--a
Survey." arXiv preprint arXiv:2312.07563 (2023).