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## Hierarchical Clustering in Scale-Free Universes: Caption

These two animations show a projection of matter-density in two numerical
simulations of gravitational clustering in an expanding universe. They
represent the time evolution of the matter in a fixed volume of each
simulated universe. Millions of particles of pure dark matter were tracked in these 3-dimensional simulations, but the movies presented here are 2-D projections of the resulting data.
Two distinct though related algorithmic approaches to modelling were
attempted.

### Gravitational instability with n=-2, "scale-Free" spectrum; P3M code; 128^3 particles

In the first simulation, a P3M code was run on NCSA's Convex C-3880, using 2 millions particles,
with a power spectrum corresponding to P = 1/K^2.
### Gravitational instability with n=0, "scale-free" spectrum; PM code; 256^3
particles on a 512^3 mesh

The second simulation was more computationally intensive. 16 million particles were used and the calculations were performed on NCSA's CM-5.
The starting conditions or"initial power spectrum" were also different in that P = a constant.

- Researcher: Edmund Bertschinger, Dept. of Physics, Massachusetts
Institute of Technology
- Visualization: Edmund Bertschinger
- Post-Production: NSCA Media Technology Resources Group
- Copyright (c)1994 and 1995, Massachusetts Institute of Technology

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#### Copyright, (c) 1995: Board of Trustees, University of
Illinois

NCSA. Last modified, 10/11/95