Strong shock in a uniform expanding universe. Approximate and exact
  solutions of self-similar equations
  Self-similar solution is obtained for propagation of a strong shock, in a
flat expanding dusty Friedman universe. Approximate analytic solution was
obtained earlier, using relation between self-similar variables, equivalent to
the exact energy conservation integral, which was obtained by L.I. Sedov for
the strong explosion in the static uniform medium. Numerical integration of
self-similar equation is made here, giving an exact solution of the problem,
which is rather close to the approximate analytic one. The differences between
these solutions are most apparent in the vicinity of the shock. For polytropic
equation of state, self-similar solutions exist in more narrow interval of the
adiabatic power than in the static case.
