-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/Zero.h

@@ -64,7 +64,7 @@ template<typename MatrixType> class Zero : NoOperatorEquals,
     }
     
   protected:
-    int m_rows, m_cols;
+    const int m_rows, m_cols;
 };
 
 /** \returns an expression of a zero matrix.
@@ -146,4 +146,17 @@ bool MatrixBase<Scalar, Derived>::isZero
   return true;
 }
 
+/** Sets all coefficients in this expression to zero.
+  *
+  * Example: \include MatrixBase_setZero.cpp
+  * Output: \verbinclude MatrixBase_setZero.out
+  *
+  * \sa class Zero, zero()
+  */
+template<typename Scalar, typename Derived>
+Derived& MatrixBase<Scalar, Derived>::setZero()
+{
+  return *this = Zero<Derived>(rows(), cols());
+}
+
 #endif // EIGEN_ZERO_H