Genius is a general purpose calculator program similiar in some aspects to BC, Matlab or Maple. It is useful both as a simple calculator and as a research or educational tool. The syntax is very intuitive and is designed to mimic how mathematics is usually written. GEL is the name of its extention language (stands for "Genius Extension Language", clever huh?), in fact, a large part of the standard genius functions are written in GEL itself.
