Pythia 8 Guidelines for Code Contributions and Authorship

Contributions to the Pythia 8 source code

On the Pythia web pages and documentation, contributions to the development of Pythia 8 are acknowledged in four categories (described in more detail under the respective headings below):

Contributions of the first type are documented in the program’s Update History. The latter three are also acknowledged on the front page of Pythia’s HTML manual.

Bug fixes and incremental updates

Many people have contributed to bug fixes and incremental updates of Pythia 8. Such contributions are usually acknowledged in direct connection with the corresponding entry in Pythia’s Update History.

Frequent examples are reports by users of unexpected “suspicious behaviour” encountered in the context of some specific study. This is often due to the use case simply going beyond Pythia’s intended limits of applicability, but does sometimes point to genuine bugs in the program. We are grateful for such reports, which can help to weed out bugs that would otherwise live on in the code, or can help us document Pythia’s intended uses and limits of applicability better.

Other examples include more technical reports that a piece of code fails to conform to a specified standard, produces undefined behaviour in some context, or violates thread safety, for instance. Such reports have even occasionally been accompanied by explicit patches that correct the problem. When that is possible, it is a major help, vastly reducing the workload on our side.

In cases where further examination is likely to be needed by the authors, standalone main programs that reproduce the behaviour are crucially important, so we request that such programs be included when users report suspicious behaviour, along with relevant input cards/settings and/or (small) examples of input files, as appropriate.

Further Contributions

Further Contributions are typically results of standalone research or development projects by non-authors, deemed of sufficient interest and quality to include in the main Pythia distribution, assuming the contributors want to do this and are willing to help make it happen. Further Contributions can also represent permission to include into Pythia a piece of code that exists separately, with permission to distribute that code together with Pythia.

After the contribution has been merged into Pythia (including relevant documentation), the original contributor is “off the hook”; the Pythia team agrees to assume the main responsibility for further maintenance and support of the contributed code, and unless agreed otherwise there is no expectation of continued development on the part of the original contributor. They may of course still be consulted in case of questions.

Further Contributions can span from extended student projects to smaller, more targeted code contributions such as interfaces to external libraries.


Authors, in addition to making substantial contributions to the code, also accept ongoing active responsibility for the development, support, and maintenance of Pythia. Each author agrees to one or more areas of scientific, technical, and/or administrative responsibilities, for which they are the main go-to person, so that:

Collegiate, collaborative, and inclusive conduct is expected at all times.

When joining the collaboration, a new author’s area of responsibility is typically limited to the substantial contribution that qualifies them for authorship in the first place. In such cases, authorship would typically be considered after the substantial contribution has passed review by a (non-supervisor) collaboration member and is being included in a public release, though individual cases may vary.

Since Pythia is a collaborative effort, the need sometimes also arises for authors to accept responsibilities for further areas, e.g., when new “further contributions” are added, or when current authors leave the collaboration.

Changes to the author list and to areas of responsibilities for existing authors are discussed with and agreed upon collectively by the Triumvirate (see Organisation below).

Former Authors

Former Authors are authors whose active/ongoing responsibilities have ceased and who have therefore effectively left the collaboration.

There is no expectation of continued development on the part of the former author, though they may be contacted in case of questions.

Typically, former authors are expected to remain on the author list for a period of roughly a year after leaving the collaboration, but final decisions will be made between the Triumvirate and the leaving author.

Authors can of course also request to leave the collaboration at any time.

Benefits of Contributing to Pythia 8

This section collects some brief points highlighting beneficial aspects of being a Pythia contributor.

A vessel for bringing your science to others. Implementing a physics model in a publicly accessible event generator like Pythia means it will be available for others to use and base their own studies on.

Science that you can use and build on. A sustained engagement means you can build on your previous work (and that of your collaborators) to make further advances with higher degrees of complexity / accuracy / detail / efficiency.

Improving Pythia for others. Since Pythia is used by many people for many purposes, improving it by even a simple bug fix has follow-on effects improving it for the next person(s) to use it. Likewise, tuning and similar studies can help ensure that lessons learned are passed on.

Review of code, modelling assumptions, implementation, and documentation. If you are a contributor, your contribution will be reviewed, both in terms of physics and in terms of code quality and implementation, documentation, and examples. It will also be subjected to validation checks. All of this may improve it, and often you learn in the process. As a Pythia author, you will both review and be reviewed. This also exposes you to new physics ideas, new algorithmic tools and tricks, new ways of writing and interfacing codes, new mathematical techniques, etc.

Collaboration network. You can engage in collaborative science projects with the Pythia team and participate in Pythia meetings and events, and/or with the wider MC community. The latter is represented in particular by the multi-institute MCnet collaboration which also includes the Herwig, Sherpa, and MadGraph_aMC@NLO projects, in addition to Rivet and a few other, more specialised projects.

Opportunities for talks. Sometimes we receive external requests for Pythia talks at workshops and at summer schools, which are allocated among the author team and contributors.

Opportunities for training. For example, attending event-generator summer schools and/or doing studentship projects with Pythia authors.

Opportunities for teaching experience. For example, giving summer school lectures and/or leading Pythia tutorials.

Organisation of Pythia 8

The Pythia collaboration has the following three main administrative / managerial roles (also called the “triumvirate”): Spokesperson, Codemaster, and Webmaster. There can also be deputies to these roles. Their main duties are as follows:


Technical lead/Codemaster


Experimental Contact Persons In addition to the roles above, Pythia Collaboration members can act as designated contacts for specific experiments. Typically, this involves actively engaging with the MC and analysis groups in the corresponding experiment to understand if there are Pythia-related issues that should be brought up with the Pythia Collaboration, and facilitating the propagation of new Pythia developments back to the experiment.

Pythia Meetings