https://jakevdp.github.io/PythonDataScienceHandbook/04.08-multiple-subplots.html
## axes are in a two-dimensional array, indexed by [row, col]
fig, ax = plt.subplots(2, 3, sharex='col', sharey='row')
for i in range(2):
for j in range(3):
ax[i, j].text(0.5, 0.5, str((i, j)),
fontsize=18, ha='center')
In comparison to plt.subplot(), plt.subplots() is more consistent with Python's conventional 0-based indexing.
for i in range(1, 7):
plt.subplot(2, 3, i)
plt.text(0.5, 0.5, str((2, 3, i)),
fontsize=18, ha='center')