The integrable initial-boundary value problem on a semiline: nonlinear Schrodinger and sine-Gordon equations

The initial-boundary value problem on a semiline for the nonlinear Schrodinger or sine-Gordon equation is reduced to the problem on a line with special symmetry conditions. These conditions can be written in terms of scattering data in the framework of the inverse scattering transform. The reduction is done by means of a Backlund transform.