  We find clusters and superclusters of galaxies using the Data Release 1 of
the Sloan Digital Sky Survey. We determine the luminosity function of clusters
and find that clusters in a high-density environment have a luminosity a factor
of ~5 higher than in a low-density environment. We also study clusters and
superclusters in numerical simulations. Simulated clusters in a high-density
environment are also more massive than those in a low-density environment.
Comparison of the density distribution at various epochs in simulations shows
that in large low-density regions (voids) dynamical evolution is very slow and
stops at an early epoch. In contrast, in large regions of higher density
(superclusters) dynamical evolution starts early and continues until the
present; here particles cluster early, and by merging of smaller groups very
rich systems of galaxies form.
