Graph Signal Processing, Fourier Transform, Graph Fourier Transform, Eigenvectors, Spectral Analysis.
https://www.youtube.com/watch?v=MOvn9DNZeAg [5] https://en.wikipedia.org/wiki/Eigendecomposition_of_a_matrix [6] https://en.wikipedia.org/wiki/Circulant_matrix [7] Sandryhaila et al (2013) Discrete signal processing on graphs [8] https://en.wikipedia.org/wiki/DFT_matrix [9]