docs: def plot_plate_limits(axis, ridges, trenches, ymin, ymax):
      """plot lines designating ridges and trenches"""
      for trench in trenches:
          axis.axvline(
              x=trench, ymin=ymin, ymax=ymax,
              color='red', ls='dashed', alpha=0.4)
      for ridge in ridges:
          axis.axvline(
              x=ridge, ymin=ymin, ymax=ymax,
              color='green', ls='dashed', alpha=0.4)
      axis.set_xlim(0, 2 * np.pi)
      axis.set_ylim(ymin, ymax)