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Welcome to the GRTresna wiki!

We have put together the following set of documentation which we hope will help you to get started using GRTresna. A contents bar should be shown on the right hand side of the wiki (or below if you are on a small screen) to help you navigate the documentation.

Here are some suggestions on where to start depending on what you want to know:

• I want to know if GRTresna is the right code for my research project

The current capabilities of the GRTresna code are detailed on the page Capabilities. Note that GRTresna is not really designed to be used as a "black box" code for generating initial data - you will need to be willing to take time to understand how the code works, and to write new tools for your specific application if required. The code is designed so as to be easy and robust to adapt to new problems, but that adaptability inevitability comes at a cost in terms of simplicity of use.

In particular, if you are a supervisor planning to ask your student to work with GRTresna, please consider whether you have sufficient background in numerical relativity and C++ coding to support them properly. We are unable to provide in depth support and whilst we have done our best to make it accessible, the code is far from straightforward for new users, especially those without an HPC background.

• I want to know how to compile and run some examples to see how it works, like binary black hole or cosmology initial data

You will need to follow the Getting started and Making your own examples parts of the wiki. It is designed to be worked through sequentially and assumes only a basic knowledge of the command line at the level of a new PhD student (we've all been there...). The two existing examples in GRTresna - a scalar field profile around a BH and a cosmological scalar field spacetime - both interface directly with particular Examples in the GRChombo NR code, so that you should be able to take the hdf5 output of this code, and provide it as the restart file for the evolution code in these examples. You might also be able to restart from a GRTresna output if you are using a different NR evolution code than GRChombo. However, this will depend on the specific details of your code.

Note that although some guidance on laptop compilation is given, to run any kind of meaningful example you will need access to a high performance computing cluster as the files generated are very large and memory intensive.

• I have some experience in numerical relativity and want to understand how to use and amend the code for my research project

You will probably still need to follow the compilation instructions in Getting started before moving on to the sections on Making your own examples. We then give more detailed guidance on the code structure and particular aspects you may want to modify in Structure of GRTresna. These pages only give a broad outline of the structure of the code and our design philosophy for new examples. If you need further guidance you should contact us, and we will do our best to help. (However, note that the informal GRTL motto is "if you want it, you build it".) Please note our License and Citation guidance.

• I use GRTresna and I want to report a bug

Please file an issue in GitHub detailing the exact version of the code you are using (ideally identified with the commit hash) and provide sufficient detail for us to recreate the problem. You can also Contact us, but raising an issue is preferred if the problem is code related.

• I use GRTresna and I want to contribute to the code

Great! Please see Contributing to GRTresna for more details.

DISCLAIMER: Whilst we have done our best to only include things which are well tested, we can't guarantee that everything works perfectly. Use of GRTresna is at your own risk!