A “1-2-1” matrix is tridiagonal with a diagonal of all twos and sub- and super-diagonals of all ones.
OneTwoOne
ElOneTwoOne_i
ElOneTwoOne_s
ElOneTwoOne_d
ElOneTwoOne_c
ElOneTwoOne_z
ElOneTwoOneDist_i
ElOneTwoOneDist_s
ElOneTwoOneDist_d
ElOneTwoOneDist_c
ElOneTwoOneDist_z