The critical point and the p-norm of the Hilbert L-matrix

Abstract The Hilbert L-matrix A s = [ a i j ( s ) ] , where a i j ( s ) = 1 / ( max ⁡ { i , j } + s ) with i , j ≥ 0 , was introduced in [3] . As a surprising property, we showed that its 2-norm is constant for s ≥ s 0 , where the critical point s 0 is unknown but relies in the interval ( 1 / 4 , 1 / 2 ) . In this note, using some delicate calculations we sharpen this result by improving the upper and lower bounds of the interval surrounding s 0 . Moreover, we establish that the same property persists for the p-norm of A s matrices.