The matrix $Z_n$ is an $n \times n$ tricirculant matrix with 1's on the sub-diagonal and super-diagonal, and also on the $(1, n)$ and $(n, 1)$ positions. This means that $Z_n$ is a circulant matrix where the first row is of the form $[0, 1, 0, \dots, 0, 1]$, and
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