anchor.diff:                             (prs 'float  n))
         ;; with neighbor map
         (with-neighbor-map (nbr info box-min box-max delta capacity)
  +        ;; print # of particles
  +        (format t "~A particles~%" n)
           ;; apply given initial condition
           (initialize x v particles)
           ;; copy initial position and velocity to device memory
  
positive.code: 
  (defkernel poly6-kernel (float ((x float4)))
    (let ((r (norm x)))
      (return (* (/ 315.0 (* 64.0 pi (pow h 9.0)))
                 (pow (- (* h h) (* r r)) 3.0)))))
  
  (defun poly6-kernel-cpu (x)
    (let ((r (norm-cpu x)))
  
negative.code: 
  (defkernel rap-visc-kernel (float ((x float4)))
    (let ((r (norm x)))
      (return (* (/ 45.0 (* pi (pow h 6)))
                 (- h r)))))
  
  (defun rap-visc-kernel-cpu (x)
  