Add Coxeter3, a llibrary for the study of combinatorial aspects of Coxeter group

theory, to be used by SageMath 9.3.

1 files changed, 63 insertions, 0 deletions

diff --git a/math/coxeter3/files/patch-sage.cpp b/math/coxeter3/files/patch-sage.cpp
new file mode 100644
index 000000000000..e77896ba2233
--- /dev/null
+++ b/math/coxeter3/files/patch-sage.cpp
@@ -0,0 +1,63 @@
+--- sage.cpp.orig	2021-01-24 16:21:00 UTC
++++ sage.cpp
+@@ -0,0 +1,60 @@
++/*
++  Coxeter version 3.0 Copyright (C) 2009 Mike Hansen
++  See file main.cpp for full copyright notice
++
++  Patch from Jeroen Demeyer <jdemeyer@cage.ugent.be>,
++  borrowed by SageMath: Add Sage interface.
++
++*/
++
++#include "sage.h"
++
++namespace sage {
++
++  void interval(List<CoxWord>& list, CoxGroup& W, const CoxWord& g, const CoxWord& h)
++
++  /*
++     Returns a list of the elements in the Bruhat interval between g and h.
++     Note that this assumes that g and h are in order.
++   */
++  {
++    if (not W.inOrder(g,h)) {
++      return;
++    }
++
++    W.extendContext(h);
++
++    CoxNbr x = W.contextNumber(g);
++    CoxNbr y = W.contextNumber(h);
++
++    BitMap b(W.contextSize());
++    W.extractClosure(b,y);
++
++    BitMap::ReverseIterator b_rend = b.rend();
++    List<CoxNbr> res(0);
++
++    for (BitMap::ReverseIterator i = b.rbegin(); i != b_rend; ++i)
++      if (not W.inOrder(x,*i)) {
++        BitMap bi(W.contextSize());
++        W.extractClosure(bi,*i);
++        CoxNbr z = *i; // andnot will invalidate iterator
++        b.andnot(bi);
++        b.setBit(z);   // otherwise the decrement will not be correct
++      } else
++        res.append(*i);
++
++    schubert::NFCompare nfc(W.schubert(),W.ordering());
++    Permutation a(res.size());
++    sortI(res,nfc,a);
++
++    list.setSize(0);
++    for (size_t j = 0; j < res.size(); ++j) {
++      CoxWord w(0);
++      W.schubert().append(w, res[a[j]]);
++      list.append(w);
++    }
++
++    return;
++  }
++
++}