X-Git-Url: https://ginac.de/ginac.git//ginac.git?a=blobdiff_plain;f=ginac%2Futils.h;h=7018bc9511a02584ffb885b81bf0cffb9d183a1b;hb=42ae6db8ba904362337098c508d168cffb9280eb;hp=fa6f54a589483a739600796a588541cf9252e42b;hpb=97af29c12bb3074cfb4e674d71000f0712c51ba2;p=ginac.git

diff --git a/ginac/utils.h b/ginac/utils.h
index fa6f54a5..7018bc95 100644
--- a/ginac/utils.h
+++ b/ginac/utils.h
@@ -138,6 +138,26 @@ OutputIterator mymerge3(InputIterator1 first1, InputIterator1 last1,
     }
 }
 
+// Compute the sign of a permutation of a vector of things.
+template <typename T>
+int permutation_sign(vector<T> s)
+{
+    if (s.size() < 2)
+        return 0;
+    int sigma = 1;
+    for (typename vector<T>::iterator i=s.begin(); i!=s.end()-1; ++i) {
+        for (typename vector<T>::iterator j=i+1; j!=s.end(); ++j) {
+            if (*i == *j)
+                return 0;
+            if (*i > *j) {
+                iter_swap(i,j);
+                sigma = -sigma;
+            }
+        }
+    }
+    return sigma;
+}
+
 // Collection of `construct on first use' wrappers for safely avoiding
 // internal object replication without running into the `static
 // initialization order fiasco'.  This chest of numbers helps speed up