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We present an algorithm which is designed to allow the efficient identification and preliminary dynamical analysis of thousands of structures and substructures in large N-body simulations. First we utilise a refined density gradient system (based on DENMAX) to identify the structures, and then apply an iterative approximate method to identify unbound particles, allowing fast calculation of bound substructures. After producing a catalog of separate energetically bound substructures we check to see which of these are energetically bound to adjacent substructures. For such bound complex subhalos, we combine components and check if additional free particles are also bound to the union, repeating the process iteratively until no further changes are found. Thus our subhalos can contain more than one density maximum, but the scheme is stable: starting with a small smoothing length initially produces small structures which must be combined later, and starting with a large smoothing length produces large structures within which sub-substructure is found. We apply this algorithm to three simulations. Two which are using the TPM algorithm by Bode et al. (2000) and one on a simulated halo by Diemand (2004). For all these halos we find about 5-8% of the mass in substructures.
Direct $N$-body simulations of star clusters are accurate but expensive, largely due to the numerous $mathcal{O} (N^2)$ pairwise force calculations. To solve the post-million-body problem, it will be necessary to use approximate force solvers, such a
We discuss the relation between the output of Newtonian N-body simulations on scales that approach or exceed the particle horizon to the description of General Relativity. At leading order, the Zeldovich approximation is correct on large scales, coin
In the next decade, cosmological surveys will have the statistical power to detect the absolute neutrino mass scale. N-body simulations of large-scale structure formation play a central role in interpreting data from such surveys. Yet these simulatio
The aim of this paper is to clarify the notion and cause of overmerging in N-body simulations, and to present analytical estimates for its timescale. Overmerging is the disruption of subhaloes within embedding haloes due to {it numerical} problems co
Gravitational N-body simulations, that is numerical solutions of the equations of motions for N particles interacting gravitationally, are widely used tools in astrophysics, with applications from few body or solar system like systems all the way up