Doc: spines arrows example (#17180)

ImportanceOfBeingErnest · web-flow · commit f369b105e615 · 2020-04-18T14:15:49.000+02:00
diff --git a/examples/axisartist/demo_axisline_style.py b/examples/axisartist/demo_axisline_style.py
@@ -4,6 +4,11 @@
 ================
 
 This example shows some configurations for axis style.
+
+Note: The `mpl_toolkits.axisartist` axes classes may be confusing for new
+users. If the only aim is to obtain arrow heads at the ends of the axes,
+rather check out the :doc:`/gallery/recipes/centered_spines_with_arrows`
+example.
 """
 
 from mpl_toolkits.axisartist.axislines import SubplotZero
diff --git a/examples/recipes/centered_spines_with_arrows.py b/examples/recipes/centered_spines_with_arrows.py
@@ -0,0 +1,35 @@
+"""
+===========================
+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"].set_position(("data", 0))
+ax.spines["bottom"].set_position(("data", 0))
+# Hide the top and right spines.
+ax.spines["top"].set_visible(False)
+ax.spines["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()
diff --git a/examples/ticks_and_spines/spine_placement_demo.py b/examples/ticks_and_spines/spine_placement_demo.py
@@ -4,6 +4,9 @@
 ====================
 
 Adjusting the location and appearance of axis spines.
+
+Note: If you want to obtain arrow heads at the ends of the axes, also check
+out the :doc:`/gallery/recipes/centered_spines_with_arrows` example.
 """
 import numpy as np
 import matplotlib.pyplot as plt
