Protasov's conjecture on spectrum-maximizing and spectrum-minimizing products

From papers

Let rr be an odd integer, and let A1,A2A_1,A_2 be the (r1)×(r1)(r-1)\times(r-1) matrices defined by

(As)ij=1if 2s2jirs+1,(A_s)_{ij}=1\quad\text{if }2-s\leq 2j-i\leq r-s+1,

and (As)ij=0(A_s)_{ij}=0 otherwise, for s=1,2s=1,2. A product is an s.m.p. if it is a spectrum-maximizing product, and an s.l.p. if it is a spectrum-minimizing product. Protasov's conjecture. For every odd rr, one of the two products A1A_1 and A1A2A_1A_2 is an s.m.p. and the other is an s.l.p. The conjecture concerns exact extremal products for the joint and lower spectral radii of this matrix family; the supplied source states it as unresolved.

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Primary source

Nicola Guglielmi and Vladimir Protasov, “Exact computation of joint spectral characteristics of linear operators”, arXiv:1106.3755 (2011).

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