2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/107812We consider the Lagrangian formalism of the deformations of Whitham systems having Dubrovin-Zhang form. As an example the case of modulated one-phase solutions of the non-linear "V-Gordon" equation is considered.24 pages, Latex, 2 figuresExactly Solvable and Integrable Systemstext