Frequently Asked Questions

This is a list of Frequently Asked Questions about EOS. Feel free to suggest new entries!

How Do I …

… use EOS within a virtual Python environment?

We highly recommend to use EOS within a virtual Python environment. To do so, you need to install the virtualenv package, and then create a new virtual environment:

pip3 install virtualenv
virtualenv --python=python3 ~/eos

The new virtual environment will now be activated. That means, the python (and pip) command will now execute the local binary instead of a system-wide one. At any later point, you can (re-)activate the virtual environment by running the following command:

source ~/eos/bin/activate

While activated, you can install a binary distribution of EOS using pip install eoshep. If you plan to install EOS from source, as discussed in the installation section, you must set the prefix to match the path to your virtual environment, here: ~/eos.

You most likely want to install jupyter and notebook. To be able to access the virtual environment from the notebook interface, you also need to install it (details here). While activated, execute the following:

pip install jupyter notebook
python -m ipykernel install --user --name venv-eos --display-name "python3 with EOS"

You can now use jupyter with python -m jupyter notebook and choose python3 with EOS as a kernel.

To deactivate the virtual environment, run


Of course, you can choose a different directory than ~/eos to host your virtual environment. Please see the virtualenv documentation for more information.

… use EOS remotely?

Since EOS can be used from within a Jupyter notebook, you can use it on a remote Linux computer. We assume that remote computer has the hostname `REMOTE_HOST`. We further assume that you can connect to that computer through a secure shell, via `ssh REMOTE_HOST` or some similar command. Last but not least, we assume that you have installed EOS on the remote computer, e.g. via the Python Package Index (PyPI): `pip3 install eoshep`. To use EOS on the remote computer through your local computer’s browser, you need to slightly change your connection details. Use `ssh -L 8888:localhost:8888 REMOTE_HOST` to connect. Now you can run `jupyter-notebook --no-browser`, which will provide you with some output that looks as follows

To access the notebook, open this file in a browser:
Or copy and paste one of these URLs:

Copy one of these links, making sure to include the lengthy token, and navigate to it in the web browser on your local computer. You will be able to use EOS within an interactive Python environment.

You can make this more persistent by configuring your SSH connection to `REMOTE_HOST`. Please see the documentation of your local computer’s secure shell program.

… use and develop EOS on Windows?

EOS can be used on Windows through the Windows Subsystem for Linux (WSL), which is offered and developed by Microsoft themselves. The installation of WSL is described in detail here. The installation provides you with a Linux container in a virtual machine. From here on, you can follow the instructions for the installation method of your choosing described for EOS under Linux. If you would like to make adaptions to the code for a project using EOS and/or contribute to its development, we recommend using the Visual Studio Code editor as your development environment. It supports connecting natively to the WSL container if you follow these steps.

… check the installation?

You can test with a single command that EOS is available as a python module:

python3 -c "import eos; print(eos.__doc__)"

Please verify that the command prints a description of the EOS module:

EOS is a software package that addresses several use cases in the field of high-energy flavor physics (HEP). [...]

If you built and installed from the source code and the import fails, i.e. you see ModuleNotFoundError: No module named 'eos', the module was either not installed with make install or the PYTHONPATH is not configured correctly.

If you installed via pip and the output description is incorrect or None, you have another module installed that is also named eos. Mind that the package name for the pip3 install command is eoshep.

… choose which tag to use for \(b \to s \ell \ell\) observables

The contributions from non-local operators in \(b \to s \ell \ell\) observables can be estimated with different theoretical approaches, usually not valid in the same energy range, based on different input parameters and different theoretical assumptions. Depending on the analysis under consideration, the user can choose between these approaches by specifying an option called tag. As different tags hide completely different assumptions, we have made this option mandatory.

We collect here the different tags used in EOS and the corresponding references.





Absence of any non-local contributions.


Calculation of the non-local contribution based on the framework of QCD factorization and a perturbative treatment of the intermediate quark states. This approach is expected to yield sensible results only for \(q^2 \ll 4 m_c^2\).

[BFS:2001A], [BFS:2004A]


Calculation of the non-local contributions in a local OPE. This approach is expected to yield sensible results only for \(q^2\)-integrated observables above the open-charm threshold.



Parametrization based on unitarity and analyticity valid for small dilepton masses below the \(\psi(2S)\) state.

[GvDV:2020A], [GRvDV:2022A]