How to add third level of ticks in Python Matplotlib?

To add third level of ticks in Python Matplotlib, we can take the following steps −

• Set the figure size and adjust the padding between and around the subplots.
• Create t and s data points using numpy.
• Create a figure and a set of subplots.
• Plot t and s using plot() method.
• Create a twin Axes sharing the Y-axis.
• Plot t and s using plot() method, on axis one.
• Set X-axis tick position.
• Create majors, minors and third level of ticks value (thirds).
• Set major and minor ticks locator with majors, minors and third tick values (thirds)
• Set ticks length using tick_params().
• Plot a horizontal line with gray color.
• To display the figure, use show() method.

Example

import matplotlib.pyplot as plt
import numpy as np
import matplotlib.ticker

plt.rcParams["figure.figsize"] = [7.50, 3.50]
plt.rcParams["figure.autolayout"] = True

t = np.arange(0.0, 100.0, 0.1)
s = np.sin(0.1 * np.pi * t) * np.exp(-t * 0.01)
fig, ax = plt.subplots()
plt.plot(t, s)

ax1 = ax.twiny()
ax1.plot(t, s)
ax1.xaxis.set_ticks_position('bottom')

majors = np.linspace(0, 100, 6)
minors = np.linspace(0, 100, 11)
thirds = np.linspace(0, 100, 101)

ax.xaxis.set_major_locator(matplotlib.ticker.FixedLocator(majors))
ax.xaxis.set_minor_locator(matplotlib.ticker.FixedLocator(minors))
ax1.xaxis.set_major_locator(matplotlib.ticker.FixedLocator([]))
ax1.xaxis.set_minor_locator(matplotlib.ticker.FixedLocator(thirds))

ax1.tick_params(which='minor', length=2)
ax.tick_params(which='minor', length=4)
ax.tick_params(which='major', length=6)
ax.grid(which='both', axis='x', linestyle='--')

plt.axhline(color='gray')

plt.show()

Output