Matrix t2*K(2) in Subspace 18 with Dimension 12

(K(2) is the second-order Grosse operator)

(-13*t*U)/2 -(8*t^2 + U^2)/(2*Sqrt[3]) -(Sqrt[3/2]*t*U) (4*t^2)/Sqrt[3] (Sqrt[3]*t*U)/2 -(U^2/Sqrt[3]) (3*t*U)/Sqrt[2] -(t*U)/2 Sqrt[2]*t*U (5*(2 + Sqrt[6])*t*U)/(2*Sqrt[18 - 3*Sqrt[6]]) (5*(3*Sqrt[2] - 2*Sqrt[3])*t*U)/(6*Sqrt[6 + Sqrt[6]]) -(Sqrt[3]*U^2)/2
-(8*t^2 + U^2)/(2*Sqrt[3]) (-5*t*U)/2 0 (t*U)/2 -2*t^2 t*U 0 2*Sqrt[3]*t^2 Sqrt[2/3]*(-4*t^2 + U^2) 0 0 (-3*t*U)/2
-(Sqrt[3/2]*t*U) 0 -2*t*U -(U^2/Sqrt[2]) Sqrt[2]*t*U 2*Sqrt[2]*t^2 0 0 0 0 0 0
(4*t^2)/Sqrt[3] (t*U)/2 -(U^2/Sqrt[2]) (-15*t*U)/2 t^2*(2 + U^2/(2*t^2)) 0 -(Sqrt[3/2]*U^2) (Sqrt[3]*(-4*t^2 + U^2))/2 4*Sqrt[2/3]*t^2 0 0 (3*t*U)/2
(Sqrt[3]*t*U)/2 -2*t^2 Sqrt[2]*t*U t^2*(2 + U^2/(2*t^2)) -3*t*U 0 0 Sqrt[3]*t*U -(Sqrt[6]*t*U) 0 0 0
-(U^2/Sqrt[3]) t*U 2*Sqrt[2]*t^2 0 0 -5*t*U 2*Sqrt[6]*t^2 0 -(Sqrt[2/3]*U^2) (-4*(-1 + Sqrt[6])*t^2)/Sqrt[6 - Sqrt[6]] (-4*(1 + Sqrt[6])*t^2)/Sqrt[6 + Sqrt[6]] t*U
(3*t*U)/Sqrt[2] 0 0 -(Sqrt[3/2]*U^2) 0 2*Sqrt[6]*t^2 -6*t*U 3*Sqrt[2]*t*U 0 0 0 0
-(t*U)/2 2*Sqrt[3]*t^2 0 (Sqrt[3]*(-4*t^2 + U^2))/2 Sqrt[3]*t*U 0 3*Sqrt[2]*t*U -3*t*U Sqrt[2]*t*U 0 0 0
Sqrt[2]*t*U Sqrt[2/3]*(-4*t^2 + U^2) 0 4*Sqrt[2/3]*t^2 -(Sqrt[6]*t*U) -(Sqrt[2/3]*U^2) 0 Sqrt[2]*t*U -4*t*U (-2*Sqrt[6 - Sqrt[6]]*t*U)/3 (-2*Sqrt[6 + Sqrt[6]]*t*U)/3 0
(5*(2 + Sqrt[6])*t*U)/(2*Sqrt[18 - 3*Sqrt[6]]) 0 0 0 0 (-4*(-1 + Sqrt[6])*t^2)/Sqrt[6 - Sqrt[6]] 0 0 (-2*Sqrt[6 - Sqrt[6]]*t*U)/3 (25*t^2*U)/(-6*t + Sqrt[6]*t) -(Sqrt[5/6]*t*U) 0
(5*(3*Sqrt[2] - 2*Sqrt[3])*t*U)/(6*Sqrt[6 + Sqrt[6]]) 0 0 0 0 (-4*(1 + Sqrt[6])*t^2)/Sqrt[6 + Sqrt[6]] 0 0 (-2*Sqrt[6 + Sqrt[6]]*t*U)/3 -(Sqrt[5/6]*t*U) (-25*t*U)/(6 + Sqrt[6]) 0
-(Sqrt[3]*U^2)/2 (-3*t*U)/2 0 (3*t*U)/2 0 t*U 0 0 0 0 0 (-9*t*U)/2