Fix little missed optimization.

diff --git a/ginac/power.cpp b/ginac/power.cpp
index 485fa06..491f2d3 100644 (file)
--- a/ginac/power.cpp
+++ b/ginac/power.cpp
@@ -1091,7 +1091,7 @@ public:
  *  where n = p1+p2+...+pk, i.e. p is a partition of n.
  */
 const numeric
-multinomial_coefficient(const std::vector<int> p)
+multinomial_coefficient(const std::vector<int> & p)
 {
        numeric n = 0, d = 1;
        for (auto & it : p) {