2 00 3 FLY . A parallel tree N - body code for cosmological simulations . Reference Guide

FLY is a parallel treecode which makes heavy use of the one-sided communication paradigm to handle the management of the tree structure. In its public version the code implements the equations for cosmological evolution, and can be run for different cosmological models. This reference guide describes the actual implementation of the algorithms of the public version of FLY, and suggests how to modify them to implement other types of equations (for instance the Newtonian ones). Computer for which the program is designed and others on which it has been tested: Cray T3E, Sgi Origin 3000, IBM SP Operating systems or monitors under which the program has been tested: Uni-cos 2. Memory required to execute with typical data: about 100 Mwords with 2 million-particles Number of bits in a word: 32 Number of processors used: parallel program. The user can select the number of processors ≥ 1 Has the code been vectorised or parallelized?: parallelized Number of bytes in distributed program, including test data, etc: 110 Mbytes Distribution format: tar gzip file Keywords: Parallel tree N-body code for cosmological simulations Nature of physical problem: FLY is a parallel collisionless N-body code for the calculation of the gravitational force Method of solution: It is based on the hierarchical oct-tree domain decomposition introduced by Barnes and Hut (1986) Restrictions on the complexity of the program: The program uses the leapfrog integrator schema, but could be changed by the user Typical running time : 50 seconds for each time-step, running a 2-million-particles simulation on an Sgi Origin 3800 system with 8 processors having 512 Mbytes Ram for each processor Unusual features of the program : FLY uses the one-side communications libraries: the shmem library on the Cray T3E system and Sgi Origin system, and the lapi library on IBM SP system