local
      A, B, C: MATRIX [DOUBLE]
      do
	 !LOCAL_MATRIX!A.make (...)
	 !DBLOCK_MATRIX!B.make (...)
	 !DBLOCK_MATRIX!C.make (...)
	 ...
	 B.add (A)	-- 'add_default' is selected
	 B.add (C)	-- 'add_dblock' is selected if B and C
			-- have the same block size.  Otherwise
			-- 'add_default' is selected
      end