The curve line is the contour line on the height of half amplitude. The two black points are the end points, and the two red lines are the tangent lines perpendicular to the y axis. Parameters: α=1, η 1 0 = 0 , k 1 = − 3 / 4 , p 1 = 1 , t = 0. (a) The contour line is Eq. (24), and the tangent lines are Eq. (25); (b) The contour line is Eq. (27), and the tangent lines are Eq. (28).