anchor.diff:            (set fcn (aref f (+ j nx))))
         (set (aref fn j) (+ (* c0 (+ fce fcw))
                             (* c1 (+ fcn fcs))
  -                          (* c2 fcc))))))
  +                          (* c2 fcc)))))))
   
   (defun initialize-device-memory (nx ny dx dy f)
     (let ((alpha 30.0))
  
positive.code:   (values))
  
  
  ;;; timer functions
  
  (defun start-timer ()
    (cl-stopwatch:stopwatch-reset :diffuse)
    (cl-stopwatch:stopwatch-start :diffuse))
  
  (defun stop-timer ()
    (cl-stopwatch:stopwatch-stop :diffuse))
  
  (defun elapsed-time ()
    (cl-stopwatch:stopwatch-read :diffuse))
  
  
  ;;; print functions
  
  (defun print-elapsed-time ()
    (let ((time (* (elapsed-time) 1.0e-3)))
      (format t "Elapsed Time = ~,3F [sec]~%" time)))
  
  (defun print-performance (flo)
    (let ((time (* (elapsed-time) 1.0e-3)))
      (format t "Performance = ~,2F [MFlops]~%" (* (/ flo time) 1.0e-6))))
  
  (defun print-time (cnt time)
  
negative.code:         (let ((j (index nx jx jy))
                (x (- (* dx (+ (float jx 1.0) 0.5)) 0.5))
                (y (- (* dy (+ (float jy 1.0) 0.5)) 0.5)))
            (setf (memory-block-aref f j)
                  (exp (* (- alpha)
                          (+ (* x x) (* y y)))))))))
    (sync-memory-block f :host-to-device))
  
  (defvar +block-dim-x+ 256)
  (defvar +block-dim-y+ 1)
  