## 1âA first session

To run xcas ,

- under Windows
  you must select the xcasen program in the Xcas program group,
- under Linux
  type xcas in a terminal (xterm, rxvt, ...), or from a Gnome session, select Xcas in the Education menu,
- under Mac OS X.4, 5
  click on the xcas icon in Applications.

You should see a new window with a menubar on the top (the main menubar), a tab, a line with buttons (including a status button) and a large space for this session. The cursor should be in what we call the first level of the session; that is, in the white space at the right of the number 1 just below the session menubar (otherwise click in this white space). Type, for example, 30! then hit the return key. You should see the answer and a new white space (with a number 2 at the left) ready for another entry. Try a few more operations; e.g., type 1/3+1/6 and hit return, or use the Graphic menu, Curves then plotfunc, etc.

You should now have a session with a few numbered pairs of input/answers, each pair is named a level. The levels created so far are all command lines (a command line is where you type a command following the computer algebra system syntax). Inside Xcas, there are other kinds of levels, the most frequently used being comments, programs, geometry (2-d or 3-d) and spreadsheet levels.

The most important editing operations are:

- Using the main menubar to enter an Xcas function name, for example
  Cmds->Integer->is_prime
  A dialog box will appear with short help on the function, some examples and related commands.
- Modifying an existing input field and reevaluating it after it has been modified by hitting the return key.
- Selecting a level or a group of levels with the mouse. Selected level(s) may be moved or erased.
- Using copy-paste, which follows Windows rules (Ctrl-C copy, Ctrl-X cut, Ctrl-V paste) or Linux rules (select with the mouse to copy, paste with the middle mouse button or with the paste button at the bottom).

Online help may be accessed using the main menubar Help->Index (short help, click on Details for more help inside your browser) and Help->Manuals. If you know a function name, you can also type the beginning and hit the tab key (at the left of the Q key on a qwerty keyboard).

You can save your work using the Save button or the File menu; this menu provides other disk and printing operations.

The software configuration parameters are grouped in three sections: Cas (computer algebra system), Graph (geometry and graphics), and General (everything else). The main menubar Cfg items will help you modify the configuration (for the Cas configuration you may also hit the status button, in the middle of the buttons line at the top of the session).

The buttons at the top of the session, just below the tab are:

- at the left, the help button,
- in the middle left, the Save button for quick session saving,
- in the middle, the status button (displaying Config followed by the number of digits, the angle unit, etc.), you can click on it to modify the cas configuration,
- in the middle right, a STOP button to interrupt a computation,
- at the right, a Kbd button that makes a scientific keyboard appear or disappear.
- at the far right, a x that closes the session.

In the next sections, we will explain in more detail the capabilities of the Xcas interface: online help, the different kinds of levels, the management of sessions and the configuration.