-add set...() methods and their documentation; remove Generic

-use row-major traversal when the number of columns is fixed
 and the number of rows is dynamic
-other minor changes

Eigen/src/Core/Identity.h

@@ -60,7 +60,7 @@ template<typename MatrixType> class Identity : NoOperatorEquals,
     }
     
   protected:
-    int m_rows;
+    const int m_rows;
 };
 
 /** \returns an expression of the identity matrix of given type and size.
@@ -108,5 +108,18 @@ bool MatrixBase<Scalar, Derived>::isIdentity
   return true;
 }
 
+/** Writes the identity expression into *this.
+  *
+  * Example: \include MatrixBase_setIdentity.cpp
+  * Output: \verbinclude MatrixBase_setIdentity.out
+  *
+  * \sa class Identity, identity()
+  */
+template<typename Scalar, typename Derived>
+Derived& MatrixBase<Scalar, Derived>::setIdentity()
+{
+  return *this = Identity<Derived>(rows());
+}
+
 
 #endif // EIGEN_IDENTITY_H