Designs, Codes and Cryptography

, Volume 65, Issue 1, pp 65–69

Spectral characterization of a graph on the flags of the eleven point biplane


  • A. Blokhuis
    • Eindhoven University of Technology
    • Eindhoven University of Technology

DOI: 10.1007/s10623-011-9570-5


We characterize a 55-point graph by its spectrum \({4^1, (-2)^{10}, (-1 \pm \sqrt{3})^{10}, ((3 \pm \sqrt{5})/2)^{12}}\) . No interlacing is used: examination of tr A m for m ≤ 7 together with study of the representation in the eigenspace for the eigenvalue −2 suffices.


Spectral characterization Euclidean representation Graph representation Iofinova-Ivanov graph

Mathematics Subject Classification (2000)

05C40 05Bxx 05Exx 05C38

Open Access

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© The Author(s) 2011