GNU Dionysus

This project has been decommissioned. This web page is kept here for historical purposes only.

Help Wanted!

We are currently looking for volunteers that would like to contribute to the Dionysus project. In particular, we are looking for people that would like to insert new constants in the database. Everybody is very welcome!

If you are interested, please contact jeanmichel [dot] sellier [at] gmail [dot] com

Introduction to Dionysus

Dionysus is a local machine search engine for universal constants and parameters of scientific and engineering relevance. If you develop a code and need any kind of well known constant you do not need to hard code them anymore. Just use Dionysus and it will do the job for you.

Dionysus is also useful if you need to know some well known constant but you do not have an Internet connection or you do not want to access to hundreds web pages to a simple value.

Dionysus has been developed as most carefully as possible and the author expects the package to be reliable for the plenty of values already included there.

Anytime you need a value, do not hard code it. Just ask Dionysus and it will give you the right answer. It is high consuming to look for parameters values, especially because those values are usually scattered among papers and websites, some of them being very old and/or impossible to find anymore.

Downloading Dionysus

Dionysus is available from the GNU download server via HTTP(S) and FTP. It can also be found on the GNU mirrors; please use a mirror if possible.


Let us suppose one wants to know the value of the elementary charge (i.e. the absolute value of the electron charge). One has several ways of finding this number:

  1. going to a library and look for that constant in a book
  2. browsing the web pages to find it
  3. asking Dionysus!!

The third way is actually the easiest!

Usually, this constant is denoted by the letter "e" (among engineers) or by the letter "q" (among physicists). So, one can ask Dionysus the exact value by typing one of the following commands:

  > dionysus universal.ddb elementary_charge value
  > dionysus universal.ddb q value
  > dionysus universal.ddb e value

where "universal.ddb" is a database ASCII file provided along with the current version. The value returned is:


It's REALLY easy like that! And you can ask much more than that to Dionysus!

Databases in the current version

The current version of Dionysus provides three databases:

  1. universal.ddb
    which contains the value of 46 well-known universal constants;
  2. chemistry.ddb
    which contains the atomic number of 104 chemical elements;
  3. semiconductors.ddb
    which contains 40 semiconductors constants.

Mailing lists

Announcements about Dionysus and most other GNU software are made on <>.

To subscribe to these or any GNU mailing lists, please send an empty mail with a Subject header of just “subscribe” to the relevant -request list. For example, to subscribe yourself to the GNU announcement list, you would send mail to <>. Or you can use the mailing list web interface.

Getting involved

Development of Dionysus, and GNU in general, is a volunteer effort, and you can contribute. For information, please read How to help GNU. If you'd like to get involved, it's a good idea to join the discussion mailing list (see above).


For development sources, bug and patch trackers, and other information, please see the Dionysus project page at


Dionysus is a GNU package mainly developed by Jean Michel Sellier. If you have any request or suggestion about this package you are very welcome. You can send them to: jeanmichel [dot] sellier [at] gmail [dot] com


Dionysus is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.