<html><head><title>[xgap] 2.2 What you can do with XGAP</title></head>
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<h1>2.2 What you can do with XGAP</h1><p>
<p>
XGAP graphic sheets work graphic object oriented. This means that the
basic graphic objects are not pixels but lines, rectangles, circles and so
on. Although technically everything on the screen consists of pixels
XGAP remembers the structure of your graphics via higher objects. This
has advantages as well as disadvantages. Do not expect to be able to
place pixel images into your XGAP graphic sheets. That is as of now
<strong>not possible</strong> with XGAP and probably will never be, because it is not
the idea of the design.
<p>
What you can do is create, move around and change lines, circles, text and
so forth in graphic sheets. Your programs can communicate with the user via
graphical user interfaces like mouse, menus, dialogs, and so on.
<p>
It is very easy to link this graphical environment with your programs in
the mathematical environment of <font face="Gill Sans,Helvetica,Arial">GAP</font>. So you can very quickly implement
visualizations of the mathematical objects you study. The user can select
objects, choose functions from menus and ask for more information with a
few mouse clicks.
<p>
A good example for this approach is the implementation of the interactive
Todd-Coxeter-Algorithm to compute coset tables in finitely presented
groups. It uses the graphical features of XGAP to give the user quick
and easy access to the algorithm by a few mouse clicks. This program was
written by Ludger Hippe in Aachen using XGAP3 and is currently ported to
XGAP4 and extended by Volkmar Felsch.
<p>
Another nice little example is in the <code>examples</code> subdirectory in the
XGAP distribution. It was written by Thomas Breuer (Aachen) to
demonstrate the features of XGAP. The user gets a small window with a
puzzle and can solve it using the mouse. You can test this example by
starting XGAP and <code>Read</code>ing the file <code>pkg/xgap/examples/puzzle.g</code>.
You can do this by using
<p>
<pre>
gap> ReadPkg("xgap","examples/puzzle.g");
gap> p := Puzzle(4,4);
</pre>
<p>
You do not have to invent the wheel many times. For certain mathematical
concepts like graphs, posets or lattices XGAP provides implementations
which can
be adapted to your special situation. You can use those parts of the code
you like and substitute the other parts to adapt the behaviour of the user
interface to your wishes.
<p>
<p>
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<P>
<address>xgap manual<br>Mai 2003
</address></body></html>
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