and here is the fixed-size Block class

src/Core.h

@@ -21,6 +21,7 @@ namespace Eigen {
 #include "Core/Row.h"
 #include "Core/Column.h"
 #include "Core/DynBlock.h"
+#include "Core/Block.h"
 #include "Core/Minor.h"
 #include "Core/Transpose.h"
 #include "Core/Conjugate.h"

src/Core/DynBlock.h

@@ -23,8 +23,8 @@
 // License. This exception does not invalidate any other reasons why a work
 // based on this file might be covered by the GNU General Public License.
 
-#ifndef EIGEN_BLOCK_H
-#define EIGEN_BLOCK_H
+#ifndef EIGEN_DYNBLOCK_H
+#define EIGEN_DYNBLOCK_H
 
 template<typename MatrixType> class DynBlock
   : public MatrixBase<typename MatrixType::Scalar, DynBlock<MatrixType> >
@@ -82,4 +82,4 @@ DynBlock<Derived> MatrixBase<Scalar, Derived>
                         startRow, startCol, blockRows, blockCols);
 }
 
-#endif // EIGEN_BLOCK_H
+#endif // EIGEN_DYNBLOCK_H

src/Core/MatrixBase.h

@@ -85,8 +85,8 @@ template<typename Scalar, typename Derived> class MatrixBase
     
     DynBlock<Derived> dynBlock(int startRow, int startCol,
                                int blockRows, int blockCols) const;
-    //template<int BlockRows, int BlockCols> Block<Derived, BlockRows, BlockCols>
-    //block(int startRow, int startCol) const;
+    template<int BlockRows, int BlockCols>
+    Block<Derived, BlockRows, BlockCols> block(int startRow, int startCol) const;
     
     Transpose<Derived> transpose() const;
     Conjugate<Derived> conjugate() const;

src/Core/Util.h

@@ -48,6 +48,7 @@ template<typename MatrixType> class Row;
 template<typename MatrixType> class Column;
 template<typename MatrixType> class Minor;
 template<typename MatrixType> class DynBlock;
+template<typename MatrixType, int BlockRows, int BlockCols> class Block;
 template<typename MatrixType> class Transpose;
 template<typename MatrixType> class Conjugate;
 template<typename MatrixType> class Opposite;