# File lib/date.rb, line 369
  def self.jd_to_commercial(jd, sg=GREGORIAN)
    ns = ns?(jd, sg)
    a = jd_to_civil(jd - 3, ns)[0]
    y = if jd >= commercial_to_jd(a + 1, 1, 1, ns) then a + 1 else a end
    w = 1 + (jd - commercial_to_jd(y, 1, 1, ns)) / 7
    d = (jd + 1) % 7
    if d.zero? then d = 7 end
    return y, w, d
  end