"""
===========================
Centered spines with arrows
===========================

This example shows a way to draw a "math textbook" style plot, where the
spines ("axes lines") are drawn at ``x = 0`` and ``y = 0``, and have arrows at
their ends.
"""

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots()
# Move the left and bottom spines to x = 0 and y = 0, respectively.
ax.spines[["left", "bottom"]].set_position(("data", 0))
# Hide the top and right spines.
ax.spines[["top", "right"]].set_visible(False)

# Draw arrows (as black triangles: ">k"/"^k") at the end of the axes.  In each
# case, one of the coordinates (0) is a data coordinate (i.e., y = 0 or x = 0,
# respectively) and the other one (1) is an axes coordinate (i.e., at the very
# right/top of the axes).  Also, disable clipping (clip_on=False) as the marker
# actually spills out of the axes.
ax.plot(1, 0, ">k", transform=ax.get_yaxis_transform(), clip_on=False)
ax.plot(0, 1, "^k", transform=ax.get_xaxis_transform(), clip_on=False)

# Some sample data.
x = np.linspace(-0.5, 1., 100)
ax.plot(x, np.sin(x*np.pi))

plt.show()
