The GAP 4 package "Interface to CARAT", briefly called just Carat, 
provides GAP interface routines to some of the stand-alone programs 
in the package CARAT, developed by J. Opgenorth, W. Plesken, and 
T. Schulz at Lehrstuhl B f\"ur Mathematik, RWTH Aachen. CARAT is a 
package for the computation with crystallographic groups. It is 
implemented in C, and thus needs to be compiled. It runs on Unix 
systems only.

CARAT is to a large extent complementary to the GAP 4 package
Cryst. In particular, it provides routines for the computation 
of normalizers and conjugators of finite unimodular groups in GL(n,Z),
and routines for the computation of Bravais groups, which are all 
missing in Cryst.  Furthermore, it provides also a catalogue of 
Bravais groups up to dimension 6. Cryst automatically loads Carat
when it is available, and makes use of its functions where necessary. 
The Carat package thereby extends the functionality of the package 
Cryst considerably.

Please note that the Carat package consists of the GAP interface
routines to CARAT, even though a copy of CARAT itself is included in
the distribution. All rights and responsibilities regarding CARAT
remain with its authors. The most recent version of CARAT can be
obtained at the CARAT Home Page

    http://wwwb.math.rwth-aachen.de/carat/

Questions and bug reports regarding CARAT itself should be addressed 
to the CARAT authors at

    carat@momo.math.rwth-aachen.de.

The GAP interface routines to CARAT have been written by

    Franz G\"ahler
    Fakult\"at f\"ur Mathematik 
    Universit\"at Bielefeld 
    Postfach 10 01 31 
    D-33501 Bielefeld

    gaehler@math.uni-bielefeld.de

to whom bug reports regarding these interface routines should be
addressed.


INSTALLATION

This package must be installed in the pkg subdirectory of any of
the GAP 4 root directories. We assume here that this is /gap4/pkg.

    cd /gap4/pkg
    unzoo -x carat-2.1.zoo

This creates a subdirectory carat, the home directory of this interface
package. CARAT itself can be installed anywhere on your system. 
You only have to make sure GAP finds the CARAT binaries, by making 
a symbolic link from the bin subdirectory in the home directory
of this interface package to the bin subdirectory of CARAT itself. 
In our example, we install Carat in /gap4/pkg/carat (the CARAT tar 
file should already be there):

    cd /gap4/pkg/carat
    zcat carat-2.1b1.tgz | tar pxf -
    ln -s carat-2.1b1/bin bin
    cd carat-2.1b1

This creates a subdirectory /gap4/pkg/carat/carat-2.1b1, the CARAT top level
directory. You have to edit the Makefile in that directory. In particular,
you have to set the variables TOPDIR (to /gap4/pkg/carat/carat-2.1b1), CC, 
and CFLAGS (to your favourite set of compiler options). Then do 

    make

If you build for more than one architecture, make sure to do a 
'make clean' in between.

Like any other GAP 4 package, Carat is then loaded in GAP with

    LoadPackage("carat");

This package, together with CARAT itself, takes some 210Mb of disk space,
or more, depending on the system. Some 170Mb is taken by the catalog
of Q-classes of integer matrix groups up to dimension 6. If you want
to avoid unpacking this catalog, you can create empty subdirectories

    cd /gap4/pkg/carat/carat-2.1b1
    mkdir tables
    mkdir tables/qcatalog

before making CARAT. If you want to unpack the catalog later, just
remove the empty directory tables/qcatalog, and do

    make Qcatalog