2-soliton solution of the sine-Gordon equation via Bianchi permutability:

s1= 1
s2= 2
 

                                 (e^(u + t) - e^(2u + t/2))
w(u,t) =  2arctan[-3 --------------------------]
                                    (1 + e^(3u + (3/2)t))

Time steps: t= -5, -4, ..., 0, ..., 5