> For the complete documentation index, see [llms.txt](https://docs.caterpillarproject.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.caterpillarproject.org/technical/initial-conditions.md).

# Initial Conditions

## Overview

We use the multi-scale cosmological initial conditions creator `MUSIC`. `MUSIC` is a computer program to generate nested grid initial conditions for high-resolution “zoom” cosmological simulations. A detailed description of the algorithms can be found in Hahn & Abel (2011). You can download the user’s guide [here](https://bitbucket.org/ohahn/music/downloads/MUSIC_Users_Guide.pdf) or obtain a copy of the code [here](https://people.phys.ethz.ch/~hahn/MUSIC/). Any questions should be directed to [Brendan Griffen](mailto:brendan.f.griffen%40gmail.com) and then if that fails, [Oliver Hahn](mailto:hahn%40phys.ethz.ch).

## Parameters

These are the parameter files which were used to generate the initial conditions for the *Caterpillar* project. We adopt the raw Planck (2013) cosmology and do not use 2nd order Lagrangian perturbation theory. The [user guide](https://bitbucket.org/ohahn/music/downloads/MUSIC_Users_Guide.pdf) contains all the information required to understand the following parameter files. Within each simulation directory, there is a file named `OUTPUTmusic` which gives the log of the construction of the initial conditions.