(defmethod (setf mref) ((value double-float) (matrix matrix-dfr) i j)
  (declare
   (type double-float value)
   (type fixnum i j)
   (optimize (debug 0) (safety 0) (speed 3)))
  (with-matrix-indexes (matrix i j)
    (multiple-value-bind (segment-id element-id) (floor j (the fixnum (segment-width matrix)))
      (let ((segment (aref (the (simple-array (simple-array double-float)) (segments matrix))
			   (+ (the fixnum (* i (the fixnum (number-of-segments matrix)))) segment-id))))
	(declare
	 (type fixnum segment-id element-id)
	 (type (simple-array double-float) segment))
	(setf (aref segment element-id) value)))))

;;;;;
; in: DEFMETHOD (SETF MREF) (DOUBLE-FLOAT MATRIX-DFR T T)
;     (SETF (AREF LINEAR-ALGEBRA::SEGMENT LINEAR-ALGEBRA::ELEMENT-ID)
;             LINEAR-ALGEBRA::VALUE)
; --> LET* FUNCALL SB-C::%FUNCALL (SETF AREF) SB-KERNEL:HAIRY-DATA-VECTOR-SET
; --> MULTIPLE-VALUE-BIND MULTIPLE-VALUE-CALL
; ==>
;   #'(LAMBDA (&OPTIONAL (ARRAY) (SB-INT:INDEX) &REST #:G21)
;       (DECLARE (IGNORE #:G21))
;       (DECLARE (TYPE (SIMPLE-ARRAY DOUBLE-FLOAT 1) ARRAY)
;                (TYPE DOUBLE-FLOAT SB-C::NEW-VALUE))
;       (SB-KERNEL:DATA-VECTOR-SET ARRAY SB-INT:INDEX SB-C::NEW-VALUE))
;
; note: doing float to pointer coercion (cost 13) to "<return value>"
;
; compilation unit finished
;   printed 1 note