fluid-set-boundary   xtlang

;; I don't want to reflect at boundary points
;; so just average everything.
(bind-func fluid-set-boundary
  (lambda (b:i64 x:double* Ny:i64 N:i64)
    (let ((j 0)
    (i 0)
    (lastrow (* (- Ny 1) N)))
      (dotimes (i 1 (- N 2))
        (pset! x i
         (* 0.5 (+ (pref x i)
       (pref x (+ i N)))))
        (pset! x (+ i lastrow)
         (* .5 (+ (pref x (+ i lastrow))
      (pref x (+ i (- lastrow N)))))))
      (dotimes (j 1 (- Ny 2))
  (pset! x (* j N)
         (* .5  (+ (pref x (* j N))
       (pref x (+ 1 (* j N))))))
  (pset! x (+ (* j N) (- N 1))
         (* .5 (+ (pref x (+ (* j N) (- N 1)))
      (pref x (+ (* j N) (- N 2)))))))