The Riemann Problem for the Main Model Cases of the Euler–Poisson Equations

In this paper, we construct a solution to the Riemann problem for an inhomogeneous non-strictly hyperbolic system of two equations, which is a corollary of the Euler–Poisson equations without pressure [5]. These equations can be considered for cases of attractive and repulsive forces as well as for cases of zero and nonzero underlying density background. The solution to the Riemann problem for each case is nonstandard and contains a delta-shaped singularity in the density component. In [14], solutions were constructed for the combination corresponding to the cold plasma model (repulsive force and nonzero background density). In this paper, we consider the three remaining cases.