add definition of product_tag

Eigen/src/Core/GeneralProduct.h

@@ -98,6 +98,31 @@ public:
 #endif
 };
 
+template<typename Lhs, typename Rhs> struct product_tag
+{
+private:
+  
+  typedef typename remove_all<Lhs>::type _Lhs;
+  typedef typename remove_all<Rhs>::type _Rhs;
+  enum {
+    Rows  = _Lhs::RowsAtCompileTime,
+    Cols  = _Rhs::ColsAtCompileTime,
+    Depth = EIGEN_SIZE_MIN_PREFER_FIXED(_Lhs::ColsAtCompileTime, _Rhs::RowsAtCompileTime)
+  };
+
+  enum {
+    rows_select = Rows==1 ? int(Rows) : int(Large),
+    cols_select = Cols==1 ? int(Cols) : int(Large),
+    depth_select = Depth==1 ? int(Depth) : int(Large)
+  };
+  typedef product_type_selector<rows_select, cols_select, depth_select> selector;
+
+public:
+  enum {
+    ret = selector::ret
+  };
+
+};
 
 /* The following allows to select the kind of product at compile time
  * based on the three dimensions of the product.