/* klc - for computations of type A Kazhdan-Lusztig polys
 * Copyright (C) 2010 Gregory S. Warrington
 * email: gwar@alumni.princeton.edu 
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
 * 02111-1307, USA.
 */

Compile to a binary via "gcc -O3 *.c" or its equivalent.
Run as 
  ./a.out n filename
where 
  n - determines which symmetric group S_n we are computing in.
  filename - identifies a file consisting of pairs x,w, one pair
    per line for which we wish to compute the K-L polynomial 
    P_{x,w}. 

For example, given the file "test-file" in this folder, running
  ./a.out 10 test-file 
will produce the output:

~/code/ccode/fr2/kl% ./a.out 10 test-file
0432187659 4678091235 MU 4 wlen: 23 xlen: 12 1,14,60,96,43,4 
0432817659 4678901235 MU 4 wlen: 24 xlen: 13 1,15,67,109,50,4 
0532187649 5678091234 MU 4 wlen: 24 xlen: 13 1,15,67,109,50,4 
0532817649 5678901234 MU 4 wlen: 25 xlen: 14 1,16,75,124,58,4 
4321098765 9467182350 MU 4 wlen: 31 xlen: 20 1,7,19,26,17,4 
4321908765 9467812350 MU 4 wlen: 32 xlen: 21 1,8,24,34,22,4 
5321098764 9567182340 MU 4 wlen: 32 xlen: 21 1,8,24,34,22,4 
5321908764 9567812340 MU 4 wlen: 33 xlen: 22 1,9,30,45,28,4 
0123456789 3458760129 wlen: 21 xlen: 0 1,6,13,10,1 
9876543210 0123456789 wlen: 0 xlen: 45 0
0123456789 0213456789 MU 1 wlen: 1 xlen: 0 1 

We describe the entries in the first line:
  0432187659        = x
  4678091235        = w
  MU                only included if mu(x,w) > 0
  4                 mu(x,w) if > 0, otherwise not listed
  wlen: 23          l(w)
  xlen: 12          l(x)
  1,14,60,96,43,4   P_{x,w} = 1 + 14q + 60q^2 + 96q^3 + 43q^4 + 4q^5 
  
Note that in this case mu(x,w) > 0 and indeed, 
  deg(P_{x,w}) = (23 - 12 - 1)/2 = 5.

For working in S_n, n > 10, use the corresponding ASCII symbols just
above 9, so
  10 <--> :
  11 <--> ;
  12 <--> <
  13 <--> =
  14 <--> >
  15 <--> ?
  ...
The input code could easily be rewritten to use 10 <--> a, 11 <--> b, etc., 
but I haven't bothered.