“…In the current soliton theory, the problem of rogue wave on a periodic background is a subject with considerable attention. By means of the nonlinearization of spectral problem [14] and Darboux transformation approach [15][16][17][18][19], periodic standing waves of various equations have been investigated, such as mKdV equation [20], the NLS equation [21][22][23][24][25][26], the Hirota equation [27], the sine-Gordon equation [28] and the fifth-order Ito equation [29]. However, all the above mentioned are equations with constant coefficients, and in this paper we focus on a variable-coefficient equation.…”