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<h1><font color="#663300">Documentation</font></h1>
<h3>The user interface</h3>
<p>EULER uses two windows : a text window and a graphics window.</p>
<p align="justify">The <strong>text window</strong> contains the menu and is designed for user input and output of
EULER. It is a scrollable window. You can use the scrollbar to scroll through
available text or the page up and down keys. All user input is preceded by a
prompt (>). Furthermore, there are output and comments (preceded by %). The size of the window
is saved at exit so that the window will have the same size the next time you
run EULER. (see below for <a href="#prefs">preferences</a>)</p>
<p><center><img src="images/shot1.gif"></center></p>
<p align="justify">The <strong>graphics window</strong> is used, whenever EULER <i>draws</i>
output. Unless the graphics screen has been cleared, EULER will redraw the
screen automatically. The size of the graphics window is saved at exit so that
you will get the same size the next time you run EULER (see below for
<a href="#prefs">preferences</a>).</p>
<p><center><img src="images/shot2.gif"></center></p>
<p align="justify">You can switch between both screens with the tabulator key while editing
input.</p>
<h3>Using Notebooks (.en files)</h3>
<p align="justify">The interface works as a terminal, allowing command editing, and
then interpret the commands by an <tt>return</tt> key stroke. The cursor is
shifted to the next command line. The line, on which the cursor is, is the
active command line : this is the line that is interpreted by Euler when the
<tt>return</tt> key is stroken. This version of EULER uses notebooks. i.e.,
old commands can be edited and changed, than interpreted again. Comments may be
added to commands to explain them. This is a smooth and flexible interface.</p>
<p align="justify"><strong>Note :</strong>
The most important fact about notebooks is that EULER still uses the sequence
of commands as they are executed. So if you change the value of a variable and
go to previous command, the changed value is used. You may also change a
previous command and execute it again. Its output is then replaced with the new
output and EULER proceeds to the next command.</p>
<p align="justify">Furthermore, the list of command inputs, outputs and
comments can be saved as notebook files (they are saved as <i>text files</i>) so
that they can be given to other people or can be kept as documented computations.
These files can be loaded with the <tt>Open</tt> menu command or, just by
dragging the file from an XDND protocol compatible file manager (Rox, Nautilus).
For now, I have a problem with Konqueror (??) - to be fixed. The directory
where the notebook file is located is the working directory. Euler module
file in the same directory can be loaded with the <tt>load</tt> command</p>
<p align="justify">Notebook files are different from Euler module files
(<strong>*.e</strong> files), which are collections of functions programmed
euler language , and which may be loaded with the <tt>load</tt> command.</p>
<p align="justify">You may not only change previous commands, but also delete them or insert new
commands. Use the edit menu to do this and to learn about the keyboard
shortcuts.</p>
<h3>The line editor</h3>
<p align="justify">Text can be entered after the prompt (<tt>></tt>) using the keyboard. If a letter is
wrong, it can be canceled with the <tt>backspace</tt> key or the <tt>delete</tt> key. The cursor
<tt>left</tt> and <tt>right</tt> keys position the cursor back and forth in the line. The line
editor is always in insert mode, so any character is inserted at the cursor
position. The <tt>home</tt> key positions the cursor to the beginning of the line,
and the <tt>end</tt> key to the end of the line. <tt>Escape</tt> clears all input. <tt>Shift cursor
left</tt> or <tt>right</tt> position the cursor one word to the right or left.
You can also select with the mouse, copy, cut and paste text through the X
clipboard. Finally, the
input is entered by pressing <tt>return</tt>. Then EULER will start to interpret the
command. The cursor can be at any position of the input line, when Return is
pressed.</p>
<p align="justify">Euler records the previous executed commands in an history. Previous input can be recalled in the current line with <tt>shift cursor-up</tt> and <tt>shift cursor-down</tt>.</p>
<p align="justify">Pressing the <tt>insert</tt> key extends incomplete commands. Pressing this key again
gives another extension, if there is one. The search goes through the command
history, the implemented functions, the user defined functions and the built-in
commands in that order.</p>
<p align="justify">There are some other special keys. The <tt>tabulator</tt> key switches to the
graphics screen and from there any key switches back. The <tt>escape</tt> key stops any
running EULER program and some internal functions, like the 3-dimensional
plots, the linear equation solver and the polynomial root finder.</p>
<p align="justify"><tt>Cursor-up</tt> and <tt>cursor-down</tt> position the input line to the
next or previous input. If you
execute this line, its output will be replaced by the new output. <tt>Page-up</tt> and
<tt>page-down</tt> go several pages back or forth, but do not change the cursor position.
If you want to set the cursor to a command, you can click at the correct
position with your mouse.</p>
<p align="justify">You may add comments to a command. This comment will be printed before the
command. Each line of the comment will start with <tt>%</tt>.</p>
<p align="justify">EULER input can spread over several lines by the use of "..". The two dots are
allowed at any place, where a space is acceptable. E.g.</p>
<pre>>3+ .. some comment
>4
7
>3+4
7</pre>
<p align="justify">Comments can follow the ".." and are skipped.</p>
<h3>Editing user defined functions</h3>
<p align="justify">when the <tt>function</tt> keyword is encountered at the
beginning of a line, the editor is sent in a user defined editor mode which
allows function body editing.</p>
<pre>>function f(x)
$ return x^2-1;
$endfunction
></pre>
<p align="justify">By the way, the notebook interface uses the <tt>escape</tt> key to end a function
definition, which is entered directly into the line editor. I.e., it will clear
the input line and print <tt>$endfunction</tt>. Pressing <tt>return</tt> will end the function
definition.</p>
<p align="justify">For more information about the euler functions, read the euler reference.</p>
<h3>Menus</h3>
<p align="justify">Most menu items are self explaining. However, here is a short
description of the less obvious things.</p>
<p align="justify">The <b>File</b> menu contains commands to load and save notebooks, and to create new
notebooks. This should not be mixed up with the loading of EULER files (*.e), which
contain commands to be executed, whereas notebooks contain complete sessions
with output and comments. More over, this command lets you save the graphics to
Postscript. the size of the postscript picture depends on the graphics window
size (just try and see).</p>
<p align="justify">As mentioned, each notebook command may have a comment, which you can edit
with the <b>Edit</b> menu command. It will appear in green. Paragraphs are
marked by empty lines. You may cut and paste in this window with the usual
commands (<tt>Ctrl-X</tt>, <tt>Ctrl-V</tt>, <tt>Ctrl-C</tt>). All outputs can
be deleted. Finally, you may
insert or delete the current command (including comments and output) or insert
a new command here.</p>
<p align="justify">The <b>Misc</b> menu gives access to the preference dialog and to the
<b>Demo</b> sub menu. This submenu allows you to load quickly the demo notebook
files provided with euler. The program scans the default install directory (INSTALL_DIR/share/euler/progs/)
and watch for notebook files. So, if you copy a notebook in this directory, it will
appear in the demo menu the next time euler is run.</p>
<p align="justify">The <b>Help</b> menu lets you view the documentation. There is also the
traditionnal about box.</p>
<h3><a name="prefs">The preference dialog</a></h3>
<p align="justify">The Option menu lets you set the preferences up. By default, the preferences
will be saved at EULER exit so these settings will affect the next session of
EULER as well.</p>
<p align="justify">You can set the stack size and the size of the internal graphics storage here.
Changes will be effective at the next start of EULER.</p>
<center><img src="images/pref1.gif"></center>
<p align="justify">On the next page, you can choose the number of lines per screen for the graphics
font. The higher this number, the smaller the font.</p>
<div align=center><img src="images/pref2.gif"></div>
<p align="justify">Next, you can adjust the 16 colours of EULER. These colours are used for the
text editor, the plot command, the 3D plots etc. E.g., color(n) will set the
colour for the next plot. Other commands are wirecolor, fillcolor. You may want
to put these commands into euler.cfg, which is loaded at program start.
Note that the density plots and shaded 3D plots use a different colour scheme,
which is only affected by the color nb 1.<p>
<div align=center><img src="images/pref3.gif"></div>
<p align="justify">Finally, You can set a flag to let Euler save preferences at exit (the default).
You may choose another browser than the one suggested (netscape by default). And
You can also reset the preferences to the default values.</p>
<div align=center><img src="images/pref4.gif"></div>
<h3>The resource and config files</h3>
<p align="justify">Euler uses a resource file and a config file. Both are saved in the .euler/
directory in the user's home.</p>
<p align="justify">You don't have to worry about these files since they are created by euler
itself if they don't exist.</p>
<p align="justify">The preferences are saved in the resource file named <tt>eulerrc</tt>. You may
change the values with the preference dialog or by editing the file with any text
editor.</p>
<p align="justify">The config file <tt>euler.cfg</tt> contains euler commands to be executed at
start up, like defining default path for euler files, loading default packages ...</p>
<p align="justify">The first time you run euler, a default config file is created, but you may
edit it to meet your needs. Any valid euler command will be executed.</p>
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