A TreePM code for Cosmological N-Body simulations

We describe a hybrid technique for carrying out large N-Body simulations to study formation and evolution of the large scale structure in the Universe. This hybrid code, called the treePM code, is a combination of Barnes and Hut (1986) tree code and Particle-Mesh code. Such a code combines the speed of PM simulations and the automatic inclusion of periodic boundary conditions with the high resolution of tree codes. We describe the splitting of force between the PM and the tree part, and estimate errors in force for various possible combinations. We use the error analysis to suggest an optimum configuration of the code. We present some example applications to estimate the efficacy of this code for realistic applications. We also discuss the possibility of parallelising this code