Astrophysics Source Code Library (ASCL)

You don’t know me, but if you’ve written an astrophysics code useful for producing published results, I’d like to know you, or at least know of your code. I’m Alice Allen, primary editor of the Astrophysics Source Code Library (ASCL). The ASCL is a free online reference library of (wait for it…. ) …yes! Astrophysics codes! Founded in 1999 by Robert Nemiroff and John F. Wallin, the ASCL has been dusted off, moved to a new site, and over the past year, greatly expanded. In fact, we (those of us working on the ASCL; we have an Advisory Committee and everything!) believe the ASCL is the largest collection of astrophysics codes anywhere. And the ASCL is still growing, with codes added every month.

Why a library of codes? Aside from the importance of ensuring reproducibility of one’s work (that scientific method stuff, you know), increasing falsifiability, demonstrating the integrity of a method or methods used to produce results, and increasing communication between researchers and those who study their research, working on it keeps me in at night (always a good thing). The ASCL also provides a way for astrophysicists to find codes that may be useful to their projects. We hope to provide a way for astrophysicist coders to get a little more recognition for their work, too, and are looking for a way to make the ASCL citable.

The ASCL is housed on Starship Asterisk*, the discussion forum for APOD, in its own forum called “The Engineering Deck: Astrophysics Source Code Library.” The first three threads on the ASCL’s forum front page are informational. The first is a guide to the resource; the table of contents for this thread, contained in the first post on the thread, is shown below.


Each downloadable code listed in the ASCL has its own thread; the first post of each code thread contains the following information:

  • Name of code
  • Abstract or description of code
  • Person(s) credited with writing the code
  • Link to the source code site
  • Link to a paper which discusses or uses the code
  • Unique ASCL identifier

Most entries do not house the codes themselves, but instead, list the location of a code’s information and download site. Most developers who make their codes available prefer to maintain their own websites for codes, as one of the (big!) advantages of doing so is version control. Few codes are stored on ASCL itself at this point; the ability to do so is recent. Codes which don’t have a download site can be made available on the ASCL by attaching an archive file (i.e., .zip or .gz) to the thread. Whether codes are stored on developers’ sites or on the ASCL, we want to make codes, and code sites, easier for astrophysicists to find.

Questions about and discussion of a code can be posted right on the code thread. It is not necessary to register for the APOD Starship Asterisk* forum to read and post on the ASCL site, but there is an advantage to doing so: registered users can subscribe to the forum and/or a particular thread on the forum, which alerts them via email when the thread or forum has been updated.

Codes are listed in the ASCL alphabetically by name, 100 threads to a page. Well-established codes such as Aarseth’s N-BODY codes, used now for 40 years, are included, as are new codes such as SHERA, which was introduced last month. (We paw through papers looking for codes so you don’t have to!) A full-text search capability is available; searches can be refined by iterative searching on the results. Because the ASCL has multiple pages of codes, which can be written in any language, the ability to search easily is increasingly important.

Do you know of or have a downloadable code that isn’t listed? Tell! Tell! (Please!) To get a code added, contact me at alice.allen1 at or post the suggestion on the New codes welcome thread. (Sending cookies is totally optional!)

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