Matplotlib Infinite Line Visualization

Introduction

Matplotlib is a Python library used to create visualizations for data analysis. In this tutorial, we will learn how to use axvline, axhline, and axline to draw infinite lines in Matplotlib.

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Draw vertical and horizontal lines

We can use axvline and axhline to draw vertical and horizontal lines respectively. Let's draw three horizontal lines at y=0, y=0.5, and y=1.0.

import matplotlib.pyplot as plt
import numpy as np

## Generate data
t = np.linspace(-10, 10, 100)
sig = 1 / (1 + np.exp(-t))

## Draw horizontal lines
plt.axhline(y=0, color="black", linestyle="--")
plt.axhline(y=0.5, color="black", linestyle=":")
plt.axhline(y=1.0, color="black", linestyle="--")

## Plot sigmoid function
plt.plot(t, sig, linewidth=2, label=r"$\sigma(t) = \frac{1}{1 + e^{-t}}$")
plt.xlim(-10, 10)
plt.xlabel("t")
plt.legend(fontsize=14)
plt.show()

Draw vertical line

We can use axvline to draw a vertical line at a given x position. Let's draw a vertical line at x=0.

import matplotlib.pyplot as plt
import numpy as np

## Generate data
t = np.linspace(-10, 10, 100)
sig = 1 / (1 + np.exp(-t))

## Draw horizontal lines
plt.axhline(y=0, color="black", linestyle="--")
plt.axhline(y=0.5, color="black", linestyle=":")
plt.axhline(y=1.0, color="black", linestyle="--")

## Draw vertical line
plt.axvline(color="grey")

## Plot sigmoid function
plt.plot(t, sig, linewidth=2, label=r"$\sigma(t) = \frac{1}{1 + e^{-t}}$")
plt.xlim(-10, 10)
plt.xlabel("t")
plt.legend(fontsize=14)
plt.show()

Draw arbitrary line

We can use axline to draw a line in any direction. Let's draw a line with slope 0.25 passing through the point (0, 0.5).

import matplotlib.pyplot as plt
import numpy as np

## Generate data
t = np.linspace(-10, 10, 100)
sig = 1 / (1 + np.exp(-t))

## Draw horizontal lines
plt.axhline(y=0, color="black", linestyle="--")
plt.axhline(y=0.5, color="black", linestyle=":")
plt.axhline(y=1.0, color="black", linestyle="--")

## Draw vertical line
plt.axvline(color="grey")

## Draw arbitrary line
plt.axline((0, 0.5), slope=0.25, color="black", linestyle=(0, (5, 5)))

## Plot sigmoid function
plt.plot(t, sig, linewidth=2, label=r"$\sigma(t) = \frac{1}{1 + e^{-t}}$")
plt.xlim(-10, 10)
plt.xlabel("t")
plt.legend(fontsize=14)
plt.show()

Draw diagonal lines

We can use axline with the transform parameter to draw diagonal lines with a fixed slope. Let's draw diagonal grid lines with a fixed slope of 0.5.

import matplotlib.pyplot as plt
import numpy as np

## Draw diagonal lines
for pos in np.linspace(-2, 1, 10):
    plt.axline((pos, 0), slope=0.5, color='k', transform=plt.gca().transAxes)

plt.ylim([0, 1])
plt.xlim([0, 1])
plt.show()

Summary

In this tutorial, we learned how to draw infinite lines in Matplotlib using axvline, axhline, and axline. We learned how to draw vertical and horizontal lines, arbitrary lines, and diagonal lines with a fixed slope. These functions are useful for marking special data values or for drawing grid lines to aid in data analysis.