Table of contents
Arepo is a massively parallel code for gravitational N-body systems and magnetohydrodynamics, both on Newtonian as well as cosmological backgrounds. It is a flexible code that can be applied to a variety of different types of problems, offering a number of sophisticated simulation algorithms. A description of the numerical algorithms employed by the code is given in the public release code paper. For a more in depth discussion about these algorithms, the original code paper and subsequent publications are the best resource. This documentation only addresses the question how to use the different numerical algorithms.
Arepo was written by Volker Springel (firstname.lastname@example.org) with further development by Rüdiger Pakmor (email@example.com) and contributions by many other authors (www.arepo-code.org/people). The public version of the code was compiled by Rainer Weinberger (firstname.lastname@example.org).
The Arepo code was initially developed to combine the advantages of finite-volume hydrodynamics with the Lagrangian convenience of smoothed particle hydrodynamics (SPH). To this end, Arepo makes use of an unstructured Voronoi-mesh which is, in the standard mode of operating the code, moving with the fluid in a quasi-Lagrangian fashion. The fluxes between cells are computed using a finite-volume approach, and additional spatial adaptivity is provided by the possibility to add and remove cells from the mesh according to user-defined criteria. In addition to gas dynamics, Arepo allows for additional collisionless particle types which interact only gravitationally. Besides self-gravity, forces from external gravitational potentials can also be included.
Arepo is optimized for, but not limited to, cosmological simulations of galaxy formation, and consequently can used for simulations with high dynamic range in space and time. This is in particular supported by Arepo's ability to employ adaptive local timestepping for each individual cell or particle, as well as a dynamic load and memory balancing domain decomposition. The current version of Arepo is fully MPI parallel, and has been tested in runs with >10,000 MPI tasks. The exact performance is, however, highly problem- and machine-dependent.
It is important to note that the performance and accuracy of the code is a sensitive function of some of the code parameters. We also stress that Arepo comes without any warranty, and without any guarantee that it produces correct results. If in doubt about something, reading (and potentially improving) the source code is always the best strategy to understand what is going on!
Please also note the following:
The numerical parameter values used in the examples contained in the code distribution do not represent a specific recommendation by the authors! In particular, we do not endorse these parameter settings in any way as standard values, nor do we claim that they will provide fully converged results for the example problems, or for other initial conditions. We think that it is extremely difficult to make general statements about what accuracy is sufficient for certain scientific goals, especially when one desires to achieve it with the smallest possible computational effort. For this reason we refrain from making such recommendations. We encourage every simulator to find out for herself/himself what integration settings are needed to achieve sufficient accuracy for the system under study. We strongly recommend to make convergence and resolution studies to establish the range of validity and the uncertainty of any numerical result obtained with Arepo.