trunk preprocessor: fixed bug with normcdf derivative (introduced in r2596)

git-svn-id: https://www.dynare.org/svn/dynare/trunk@2598 ac1d8469-bf42-47a9-8791-bf33cf982152

ExprNode.cc

@@ -1541,7 +1541,7 @@ TrinaryOpNode::computeDerivative(int deriv_id)
       // -(x-mu)^2/sigma^2
       t13 = datatree.AddUMinus(t12);
       // -((x-mu)^2/sigma^2)/2
-      t12 = datatree.AddDivide(t13,t11);
+      t12 = datatree.AddDivide(t13, datatree.Two);
       // exp(-((x-mu)^2/sigma^2)/2)
       t13 = datatree.AddExp(t12);
       // derivative of a standardized normal