The circulant orbit–eigenvalue conjecture

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Let GG be an uncoloured circulant graph. Write V∗VV*V for the set of unordered pairs of vertices of GG, and let Aut⁡(G)\operatorname{Aut}(G) act on V∗VV*V through its action on vertices. Let rr be the number of orbits of this action and let ss be the number of distinct eigenvalues of the adjacency matrix of GG.

Circulant orbit–eigenvalue conjecture. The number of orbits of the action of Aut⁡(G)\operatorname{Aut}(G) on V∗VV*V coincides with the number of distinct eigenvalues of its adjacency matrix; equivalently, r=sr=s.

This is stated as equivalent to the preceding conjecture in the uniform-coloured setting. The source gives no resolution, so the claim remains open here.

References

Primary source

Isobel Davies and Orlando Marigliano, “Coloured Graphical Models and their Symmetries”, arXiv:2012.01905 (2025).

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