Clean up combinatorial helpers.

[ginac.git] / ginac / utils.cpp

diff --git a/ginac/utils.cpp b/ginac/utils.cpp
index 1900e1b30ca20188eceb3d78b6e6dbed718493e1..8085ba3bdeb38673b7d0d3fadf2282765a4901ee 100644 (file)
--- a/ginac/utils.cpp
+++ b/ginac/utils.cpp
@@ -53,6 +53,19 @@ unsigned log2(unsigned n)
        return k;
 }
 
+/** Compute the multinomial coefficient n!/(p1!*p2!*...*pk!) where
+ *  n = p1+p2+...+pk, i.e. p is a partition of n.
+ */
+const numeric
+multinomial_coefficient(const std::vector<unsigned> & p)
+{
+       numeric n = 0, d = 1;
+       for (auto & it : p) {
+               n = n.add(numeric(it));
+               d = d.mul(factorial(numeric(it)));
+       }
+       return factorial(n).div(d);
+}
 
 //////////
 // flyweight chest of numbers is initialized here: