
What is CrystGap?
-----------------

CrystGap is GAP share package, which allows to perform various
computations with crystallographic groups, in particular space 
groups. Among other things, you can compute the Wyckoff positions 
and all maximal subgroups for any space group, as well as all 
space group types for a given point group. CrystGap also provides 
a fairly complete operations record for crystallographic groups, 
which allows you to do most of what you could do with other groups 
in GAP (one has to keep in mind, however, that crystallographic 
groups are usually not finite, and so certain things are not possible,
such as obtaining the list of all elements of a space group and similar 
things). Finally, CrystGaps also provides routines for dealing with
color groups, in particular color space groups.


Installation of CrystGap
------------------------

CrystGap runs on GAP 3.4.4. On some earlier versions of GAP, in 
particular those which have not all bugfixes applied, CrystGap 
does not work properly, and may return wrong results without further 
notice. We recommend that it is used only with GAP 3.4.4.

The routine WyckoffLattice only runs under XGAP, which in turn requires
Unix and the X window system. The rest of CrystGap runs on any machine
supporting GAP.

CrystGap is distributed either together with GAP 3.4.4, in which case
it also gets installed together with GAP 3.4.4, or as a separate file
cryst.zoo. In this latter case you have to unpack CrystGap in the main
GAP directory with the command

     zoo -extract cryst.zoo

If you don't have write permission in the GAP directory, you will
have to ask your system manager to install CrystGap.

After unpacking, an additional directory "cryst" should have been
created in the "pkg" subdirectory of the main GAP directory. This
is CrystGap's main directory, and should contain the file "README"
(this file), the file "init.g", and the directories "lib" (containing
the CrystGap code) and "doc" (containing the documentation).


Loading CrystGap
----------------

CrystGap is initialized by the GAP command

     RequirePackage("cryst");

After this, all CrystGap functions are available.


Documentation 
-------------

The manual of CrystGap is already included in the manual of GAP 3.4.4,
and online help for CrystGap functions is available without further
action. In the "doc" subdirectory of the CrystGap directory "cryst"
there is also a standalone version of the CrystGap manual (manual.dvi). 
The same directory contains also a preprint of a paper which describes
some of the algoritms used in CrystGap (paper.dvi). This paper will 
appear in Acta Cryst A (1997).


Problems or comments
--------------------

If you have problems with this package, wish to make comments or
suggestions, or if you find bugs, please send e-mail to any of the 
following addresses:

     Franz.Gaehler@pth.polytechnique.fr
     Bettina.Eick@math.rwth-aachen.de
     Werner.Nickel@st-and.ac.uk



