deferred class MATRIX [T->NUMERIC]
feature -- Attributes
   nrow: INTEGER      -- Number of rows
   ncolumn: INTEGER   -- Number of columns

feature -- Accessors
   item (i, j: INTEGER): T is
	 -- Return current value of item(i, j)
      require
	 valid_i:  (i > 0) and (i <= nrow)
	 valid_j:  (j > 0) and (j <= ncolumn)
      deferred
      end -- item
   put (v: T; i, j: INTEGER) is
	 -- Put value v into item(i, j)
      require
	 valid_i:  (i > 0) and (i <= nrow)
	 valid_j:  (j > 0) and (j <= ncolumn)
      deferred
      ensure
	 item (i, j) = v
      end -- put

   row (i: INTEGER): VECTOR [T] is
	 -- Returns i-th row of matrix
      require
	 valid_i:  (i > 0) and (i <= nrow)
      do -- ...
      ensure
         Result_not_void: (Result /= Void)
      end -- row
   column (j: INTEGER): VECTOR [T] is
	 -- Returns j-th column of matrix
      require
	 valid_j:  (j > 0) and (j <= ncolumn)
      do -- ...
      ensure
         Result_not_void: (Result /= Void)
      end -- column
   diagonal (k: INTEGER): VECTOR [T] is
	 -- Returns k-th diagonal of matrix
      require
	 valid_k:  (k > -nrow ) and (k < ncolumn)
      do -- ...
      ensure
         Result_not_void: (Result /= Void)
      end -- diagonal
   submatrix (i, j, k, l: INTEGER): SUB_MATRIX [T] is
	 -- Returns submatrix as defined by arguments
      do -- ...
      ensure
         Result_not_void: (Result /= Void)
      end -- submatrix

feature -- Operators
   trace:  T is do ...  end
   random (min, max: T) is do ...  end
   add (B: MATRIX [T]) is do ...  end
   mult (A, B: MATRIX [T]) is do ...  end
   LU is do ...  end
   LDLt is do ...  end
   Cholesky is do ...  end
   -- ...
end -- class MATRIX