matplotlib.axes.Axes.fill_betweenx() in Python

Matplotlib is a library in Python and it is numerical – mathematical extension for NumPy library. The Axes Class contains most of the figure elements: Axis, Tick, Line2D, Text, Polygon, etc., and sets the coordinate system. And the instances of Axes supports callbacks through a callbacks attribute.

matplotlib.axes.Axes.fill_betweenx() Function

The Axes.fill_betweenx() function in axes module of matplotlib library is used to fill the area between two vertical curves.

Syntax: Axes.fill_betweenx(self, y, x1, x2=0, where=None, step=None, interpolate=False, *, data=None, **kwargs)

Parameters: This method accept the following parameters that are described below:

• y: This parameter contains the y coordinates of the data points which are used to define the curves.
• x1: This parameter contains the x coordinates of the data points which are used to define the first curves
• x2: This parameter contains the x coordinates of the data points which are used to define the second curves. It is an optional with default value of 0.
• where: This parameter is an optional parameter. And it is used to exclude some horizontal regions from being filled.
• interpolate: This parameter is also an optional parameter. And it is the linewidth of the errorbar lines with default value NONE.
• step: This parameter is also an optional parameter. And it is used to define if the filling should be a step function or not.

Returns: This returns a PolyCollection containing the plotted polygons.

Below examples illustrate the matplotlib.axes.Axes.fill_betweenx() function in matplotlib.axes:

Example-1:

# Implementation of matplotlib function

import numpy as np
import matplotlib.pyplot as plt

y = np.arange(-5, 5, 0.01)
x1 = -y * 2 + y + 10
x2 = 2 * y + y

fig, ax = plt.subplots()
ax.plot(y, x1, y, x2, color ='black')
ax.fill_betweenx(y, x1, x2, where = x2 >x1,
                 facecolor ='green', alpha = 0.8)

ax.fill_betweenx(y, x1, x2, where = x2 <= x1,
                 facecolor ='black', alpha = 0.8)

ax.set_title('matplotlib.axes.Axes.fill_betweenx Example1')
plt.show()

Output:

Example-2:

# Implementation of matplotlib function

import numpy as np
import matplotlib.pyplot as plt

y = np.arange(0.0, 2, 0.01)
x1 = np.sin(2 * np.pi * y)
x2 = 0.8 * np.sin(4 * np.pi * y)

fig, [ax1, ax2, ax3, ax4] = plt.subplots(1, 4,
                                         sharey = True,
                                         figsize =(6, 6))

ax1.fill_betweenx(y, 0, x1, facecolor ='green')
ax1.set_title('Fill_Betweenx x1 and 0')

ax2.fill_betweenx(y, x1, 1, facecolor ='green')
ax2.set_title('Fill_Betweenx x1 and 1')

ax3.fill_betweenx(y, x1, x2, facecolor ='green')
ax3.set_title('Fill_Betweenx x1 and y2')

ax4.fill_betweenx(y, x1, x2, where = x2 <= x1,
                  facecolor ='green')

ax4.set_title('Fill_Between x1 and x2 with x2<= x1 ' )
plt.show()

Output: