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diff --git a/src/Core/Block.h b/src/Core/Block.h
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+++ b/src/Core/Block.h
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+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra. Eigen itself is part of the KDE project.
+//
+// Copyright (C) 2006-2007 Benoit Jacob <jacob@math.jussieu.fr>
+//
+// Eigen is free software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the Free Software
+// Foundation; either version 2 or (at your option) any later version.
+//
+// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+// details.
+//
+// You should have received a copy of the GNU General Public License along
+// with Eigen; if not, write to the Free Software Foundation, Inc., 51
+// Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+//
+// As a special exception, if other files instantiate templates or use macros
+// or functions from this file, or you compile this file and link it
+// with other works to produce a work based on this file, this file does not
+// by itself cause the resulting work to be covered by the GNU General Public
+// 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
+
+template<typename MatrixType, int BlockRows, int BlockCols> class Block
+  : public MatrixBase<typename MatrixType::Scalar,
+                      Block<MatrixType, BlockRows, BlockCols> >
+{
+  public:
+    typedef typename MatrixType::Scalar Scalar;
+    typedef typename MatrixType::Ref MatRef;
+    friend class MatrixBase<Scalar, Block<MatrixType, BlockRows, BlockCols> >;
+    
+    static const int RowsAtCompileTime = BlockRows,
+                     ColsAtCompileTime = BlockCols;
+
+    Block(const MatRef& matrix, int startRow, int startCol)
+      : m_matrix(matrix), m_startRow(startRow), m_startCol(startCol)
+    {
+      assert(startRow >= 0 && BlockRows >= 1 && startRow + BlockRows <= matrix.rows()
+          && startCol >= 0 && BlockCols >= 1 && startCol + BlockCols <= matrix.rows());
+    }
+    
+    Block(const Block& other)
+      : m_matrix(other.m_matrix),
+        m_startRow(other.m_startRow), m_startCol(other.m_startCol) {}
+    
+    EIGEN_INHERIT_ASSIGNMENT_OPERATORS(Block)
+    
+  private:
+    const Block& _ref() const { return *this; }
+    int _rows() const { return BlockRows; }
+    int _cols() const { return BlockCols; }
+    
+    Scalar& _write(int row, int col)
+    {
+      return m_matrix.write(row + m_startRow, col + m_startCol);
+    }
+    
+    Scalar _read(int row, int col) const
+    {
+      return m_matrix.read(row + m_startRow, col + m_startCol);
+    }
+    
+  protected:
+    MatRef m_matrix;
+    const int m_startRow, m_startCol;
+};
+
+template<typename Scalar, typename Derived>
+template<int BlockRows, int BlockCols>
+Block<Derived, BlockRows, BlockCols> MatrixBase<Scalar, Derived>
+  ::block(int startRow, int startCol) const
+{
+  return Block<Derived, BlockRows, BlockCols>
+    (static_cast<Derived*>(const_cast<MatrixBase*>(this))->ref(), startRow, startCol);
+}
+
+#endif // EIGEN_BLOCK_H