Bilinear forms graph smallest eigenvalue conjecture

Let Hq(d,e)H_q(d,e) be the bilinear forms scheme on the d×ed\times e matrices over Fq\mathbb{F}_q, where ded\leq e. In its distance-jj graph, write Bj(i)B_j(i) for the eigenvalue indexed by ii, with 0i,jd0\leq i,j\leq d.

Bilinear forms eigenvalue conjecture. For q3q\geq 3, or q=2q=2 and ded\neq e, Bj(dj+1)B_j(d-j+1) is the smallest eigenvalue in the distance-jj graph for 1jd1\leq j\leq d.

The conjecture was previously proved for q4q\geq 4 and is proved in this paper for all q2q\geq 2, so the claim is now resolved.

Sources & referencesView supporting material

Primary source

Sebastian M. Cioabă and Himanshu Gupta, “On the eigenvalues of Grassmann graphs, Bilinear forms graphs and Hermitian forms graphs”, arXiv:2102.10155 (2021).

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