"""

======================================

Infinite horizontal and vertical lines

======================================

`~.axes.Axes.axvline` and `~.axes.Axes.axhline` draw infinite vertical /

horizontal lines, at given *x* / *y* positions. They are usually used to mark

special data values, e.g. in this example the center and limit values of the

sigmoid function.

"""

import numpy as np

import matplotlib.pyplot as plt

t = np.linspace(-10, 10, 100)

sig = 1 / (1 + np.exp(-t))

plt.axhline(y=0, color="black", linestyle="--")

plt.axhline(y=0.5, color="black", linestyle=":")

plt.axhline(y=1.0, color="black", linestyle="--")

plt.axvline(color="grey")

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()

#############################################################################

#

# ------------

#

# References

# """"""""""

#

# The use of the following functions, methods, classes and modules is shown

# in this example:

import matplotlib

matplotlib.pyplot.axhline

matplotlib.pyplot.axvline

matplotlib.axes.Axes.axhline

matplotlib.axes.Axes.axvline