“…It can be seen from the literature that the PIP system can support these conditions: [17,18,55]), and m 2 < m 1 (i.e., Ar + − F − [10,13]). Equation (41) shows that under consideration of U 0 > 0 and C > 0, no shock wave will exist if A = 0 as the amplitude of the wave becomes infinite, which clearly violates the reductive perturbation method [56][57][58][59]. Thus, A can be positive (i.e., A > 0) or negative (i.e., A < 0), according to the value of other plasma parameters.…”