code: def generate_anchors(base_size=16, ratios=[0.5, 1, 2],
                       scales=2**np.arange(3, 6)):
      
  
      base_anchor = np.array([1, 1, base_size, base_size], dtype='float32') - 1
      ratio_anchors = _ratio_enum(base_anchor, ratios)
      anchors = np.vstack([_scale_enum(ratio_anchors[i, :], scales)
                           for i in range(ratio_anchors.shape[0])])
      return anchors
docs: Generate anchor (reference) windows by enumerating aspect ratios X
      scales wrt a reference (0, 0, 15, 15) window.