====== Thomas Zaslavsky (Binghamton) ======

====== Root Systems, Angle Representations, and Signed Graphs ======

===== Abstract for the Combinatorics Seminar 2013 February 19, 26 =====

Equiangular lines are lines that all make the same angle with each other. Take a unit vector in each line. The matrix of inner products of these vectors is (except for the units in its diagonal) a fixed multiple of a signed-graph adjacency matrix. Examples are the classical root systems A<sub>n</sub> and D<sub>n</sub>. I will ramble on about these topics and their connection with signed graphs and regular two-graphs for an hour or so.


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