  It is known that exact traveling wave solutions exist for families of
(n+1)-states stochastic one-dimensional non-equilibrium lattice models with
open boundaries provided that some constraints on the reaction rates are
fulfilled. These solutions describe the diffusive motion of a product shock or
a domain wall with the dynamics of a simple biased random walker. The steady
state of these systems can be written in terms of linear superposition of such
shocks or domain walls. These steady states can also be expressed in a matrix
product form. We show that in this case the associated quadratic algebra of the
system has always a two-dimensional representation with a generic structure. A
couple of examples for n=1 and n=2 cases are presented.
