'Positon' and 'dromion' solutions of the (2+1) dimensional long wave-shortwave resonance interaction equations

'Positon' and 'dromion' solutions are derived for the long wave-short wave interaction equations in a two-layer fluid. Positons are new, exact solutio ns of nonlinear evolution equations that exhibit algebraic decay in the far field. A positon solution can be generated by taking a special limit of mu lti-soliton expansion. Variation of the limiting process yields different s olutions. Dromions are exact, localized solutions of (2 + 1) dimensional (2 spatial, 1 temporal) nonlinear evolution equations that decay exponentiall y in all directions. One and higher dromion solutions are investigated, and a particular case of higher dromion solutions is considered in details. By applying another limiting procedure a new solution is generated. This meth od of 'coalescence of eigenvalues' or 'wavenumbers' is thus quite universal , and can he applied to a wide variety of expansions, not just the multi-so liton type. Finally, the case of propagation solutions on a continuous wave background is also studied.