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# 1 Introduction

This package contains GAP interface routines to CARAT, a package of programs for the computation with crystallographic groups. CARAT is implemented in C, and has been developed by J. Opgenorth, W. Plesken, and T. Schulz at Lehrstuhl B für Mathematik, RWTH Aachen. The algorithms used by CARAT are described in OPS98.

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, CARAT 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 present package thereby extends the functionality of Cryst considerably.

CARAT itself is NOT part of this package. However, for your convenience, and with the permission of the CARAT authors, a copy of CARAT has been included. It is this version with which the interface routines have been tested. The most recent version of CARAT can be obtained at the CARAT Home Page

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

The GAP interface routines to CARAT have been written by

  Franz Gähler
  Fakultät für Mathematik
  Universität Bielefeld
  Postfach 10 01 31
  D-33501 Bielefeld
  gaehler@math.uni-bielefeld.de

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

Bug reports regarding CARAT itself should be sent to carat@momo.math.rwth-aachen.de.

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