- added symmetrize() and antisymmetrize() functions

[ginac.git] / ginac / inifcns.cpp

diff --git a/ginac/inifcns.cpp b/ginac/inifcns.cpp
index b55261eb1a0072939b0a1bb43a2a317d681778ec..2667215416129be392b21891aa2d16ed6bf89139 100644 (file)
--- a/ginac/inifcns.cpp
+++ b/ginac/inifcns.cpp
@@ -523,6 +523,71 @@ ex ncpow(const ex & basis, unsigned exponent)
        return ncmul(v, true);
 }
 
+// Symmetrize/antisymmetrize over a vector of objects
+static ex symm(const ex & e, exvector::const_iterator first, exvector::const_iterator last, bool asymmetric)
+{
+       // Need at least 2 objects for this operation
+       int num = last - first;
+       if (num < 2)
+               return e;
+
+       // Sort object vector, transform it into a list, and make a copy so we
+       // will know which objects get substituted for which
+       exvector iv(first, last);
+       sort(iv.begin(), iv.end(), ex_is_less());
+       exlist iv_lst;
+       iv_lst.insert(iv_lst.begin(), iv.begin(), iv.end());
+       lst orig_lst(iv_lst);
+
+       // With n objects there are n! possible permutations
+       int num_perms = factorial(numeric(num)).to_int();
+
+       // Loop over all permutations (the first permutation, which is the
+       // identity, is unrolled)
+       ex sum = e;
+       int i = 1;
+       do {
+               next_permutation(iv_lst.begin(), iv_lst.end(), ex_is_less());
+               ex term = e.subs(orig_lst, lst(iv_lst));
+               if (asymmetric) {
+                       exlist test_lst = iv_lst;
+                       term *= permutation_sign(test_lst.begin(), test_lst.end(), ex_is_less());
+               }
+               sum += term;
+               i++;
+       } while (i < num_perms);
+
+       return sum / num_perms;
+}
+
+ex symmetrize(const ex & e, exvector::const_iterator first, exvector::const_iterator last)
+{
+       return symm(e, first, last, false);
+}
+
+ex antisymmetrize(const ex & e, exvector::const_iterator first, exvector::const_iterator last)
+{
+       return symm(e, first, last, true);
+}
+
+ex symmetrize(const ex & e, const lst & l)
+{
+       exvector v;
+       v.reserve(l.nops());
+       for (unsigned i=0; i<l.nops(); i++)
+               v.push_back(l.op(i));
+       return symm(e, v.begin(), v.end(), false);
+}
+
+ex antisymmetrize(const ex & e, const lst & l)
+{
+       exvector v;
+       v.reserve(l.nops());
+       for (unsigned i=0; i<l.nops(); i++)
+               v.push_back(l.op(i));
+       return symm(e, v.begin(), v.end(), true);
+}
+
 /** Force inclusion of functions from initcns_gamma and inifcns_zeta
  *  for static lib (so ginsh will see them). */
 unsigned force_include_tgamma = function_index_tgamma;