  Scalar cosmological perturbations are investigated in the framework of a
model with interacting dark energy and dark matter. In addition to these
constituents, the inhomogeneous Universe is supposed to be filled with the
standard noninteracting constituents corresponding to the conventional
$\Lambda$CDM model. The interaction term is chosen in the form of a linear
combination of dark sector energy densities with evolving coefficients. The
methods of discrete cosmology are applied, and strong theoretical constraints
on the parameters of the model are derived. A brief comparison with
observational data is performed.

General Relativity and Quantum Cosmology;Cosmology and Nongalactic Astrophysics;High Energy Physics - Phenomenology;High Energy Physics - Theory