Underline title

[scidam]

It is likely that tex/latex engine is not installed on your system.
Nevertheless, you can do the following: insert these lines just before rendering the figure
(plt.savefig):

# --- Insertion
from matplotlib import lines  #  put this line to header
rr = max(ax.get_ylim())
mm = np.mean(ax.get_xlim())
line = lines.Line2D([mm - 0.1, mm + 0.1], [1.05 * rr, 1.05 * rr], color='black')
line.set_clip_on(False)
ax.add_line(line)
# -------------