INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS, vol.26, no.5, pp.567-584, 1991 (Journal Indexed in SCI)
The symmetry groups associated with the quasi-linear wave equation u(tt) = [f(u(x), u(t), u, x, t)]x are investigated by employing techniques of the exterior calculus. Certain special cases corresponding to particular choices of the function f are studied in detail and some similarity solutions (invariant solutions) are constructed explicitly.