For ρ > 1 >1, let A A be a ρ -contraction on a Hilbert space H H. Letting n ≥ 1 n 1 and x x be a unit vector in H H, we show that (a) if ‖ A x ‖ = ‖ A 2 x ‖ = ⋯ = ‖ A n x ‖ ≡ c \|Ax\|=\|A²x\|= =\|Aⁿx\| c, then c ≤ ρ (ρ + n − 1) / n c (+n-1) /n, and (b) ‖ A x ‖ = ‖ A
Gau et al. (Thu,) studied this question.