18.9. Reflectionless points At = /n (n = 1, 2, . . .), the amplitude SR of the SineGordon vanishes and the scattering of

18.9. Reflectionless points At ξ = π/n (n = 1, 2, . . .), the amplitude SR of the Sine–Gordon vanishes and the scattering of the soliton–anti-soliton reduces to a pure transmission. Use the properties of the function to prove that at these values of the coupling constant the transmission amplitude becomes ST (θ) = einπ

n−1 k=1 eθ−i(πk/n) +1 eθ +e−i(πk/n)

.