code: def _ratio_enum(anchor, ratios):
          
          w, h, x_ctr, y_ctr = AnchorGenerator._whctrs(anchor)
          size = w * h
          size_ratios = size / ratios
          ws = np.round(np.sqrt(size_ratios))
          hs = np.round(ws * ratios)
          anchors = AnchorGenerator._mkanchors(ws, hs, x_ctr, y_ctr)
          return anchors
docs: Enumerate a set of anchors for each aspect ratio wrt an anchor.