  The presence of complex hierarchical gravitational structures is one of the
main features of the observed universe. Here, structure formation is studied
both for the standard ($\Lambda \rm CDM$) cosmological model and for the
Dirac-Milne universe, a matter-antimatter symmetric universe that was {\gm
recently} proposed as an alternative "coasting" cosmological scenario.
One-dimensional numerical simulations reveal the analogies and differences
between the two models. Although structure formation is faster in the
Dirac-Milne universe, both models predict that it ends shortly before the
present epoch, at cosmological redshift $z \approx 3$ for the Dirac-Milne
cosmology, and at $z \approx 0.5$ for the $\Lambda \rm CDM$ universe. The
present results suggest that the matter power spectrum observed by the Sloan
Digital Sky Survey might be entirely due to the nonlinear evolution of matter
and antimatter domains of relatively small initial dimensions, of the order of
a few tens of parsecs comoving at cosmological redshift $z =1080$.
