Coxeter

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Coxeter is a computer program for the study of combinatorial aspects of Coxeter group theory, particularly those related to the Bruhat ordering and Kazhdan-Lusztig polynomials. It is written in C++, and should run on the main types of workstation under linux or unix. The current version is now version 3.0, which is now available for beta testing.

The main capabilities of the program are the following :

• Reduced expression and normal form computations;
• Bruhat ordering;
• Ordinary Kazhdan-Lusztig polynomials;
• Kazhdan-Lusztig polynomials with unequal parameters;
• Inverse Kazhdan-Lusztig polynomials;
• Cells and W-graphs;

The program doesn't have very much in common anymore with version 1, which has been in existence for many years. The main differences, from the user's viewpoint, are the following:

• The program now works for essentially any Coxeter group (with some mild restrictions on the rank and the coefficients of the Coxeter matrix); in contrast, version 1 only worked for finite groups. Of course this doesn't mean that all computations are possible for all groups!
• Kazhdan-Lusztig polynomials are computed "on demand", instead of all at once, as version 1 did;
• The modularity of the program is very much improved, and it should be possible for a user familiar with C++ to rather easily add his own extensions; unfortunately, the quality level of the code is still a far cry from what it should be to qualify as real library. A project for the future!
• As shown by the above list, the capabilites of the program are much extended;
• A number of output formats are available, and in particular there is a GAP output format, which produces files that are directly readable by GAP/CHEVIE. The TeX output mode has been dropped, however (for now, at least.)

The author would like to stress that Coxeter was written primarily with his own research interests in mind, and that it is made available without any promise of technical or other assistance, nor of further development. It is distributed under the copyleft license of the Free Software Foundation; therefore it is not in the public domain, but may be freely copied, distributed, modified, and incorporated into other software, provided only that the modified versions be clearly identified as such, and that programs incorporating all or part of this code be in turn distributed under the copyleft license.