>>> """
=======================================
Advanced quiver and quiverkey functions
=======================================

Demonstrates some more advanced options for `~.axes.Axes.quiver`.  For a simple
example refer to :doc:`/gallery/images_contours_and_fields/quiver_simple_demo`.

Note: The plot autoscaling does not take into account the arrows, so
those on the boundaries may reach out of the picture.  This is not an easy
problem to solve in a perfectly general way.  The recommended workaround is to
manually set the Axes limits in such a case.
"""
... 
... import matplotlib.pyplot as plt
... import numpy as np
... 
... X, Y = np.meshgrid(np.arange(0, 2 * np.pi, .2), np.arange(0, 2 * np.pi, .2))
... U = np.cos(X)
... V = np.sin(Y)
... 
... ###############################################################################
... 
... fig1, ax1 = plt.subplots()
... ax1.set_title('Arrows scale with plot width, not view')
... Q = ax1.quiver(X, Y, U, V, units='width')
... qk = ax1.quiverkey(Q, 0.9, 0.9, 2, r'$2 \frac{m}{s}$', labelpos='E',
...                    coordinates='figure')
... 
... ###############################################################################
... 
... fig2, ax2 = plt.subplots()
... ax2.set_title("pivot='mid'; every third arrow; units='inches'")
... Q = ax2.quiver(X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
...                pivot='mid', units='inches')
... qk = ax2.quiverkey(Q, 0.9, 0.9, 1, r'$1 \frac{m}{s}$', labelpos='E',
...                    coordinates='figure')
... ax2.scatter(X[::3, ::3], Y[::3, ::3], color='r', s=5)
... 
... ###############################################################################
... 
... # sphinx_gallery_thumbnail_number = 3
... 
... fig3, ax3 = plt.subplots()
... ax3.set_title("pivot='tip'; scales with x view")
... M = np.hypot(U, V)
... Q = ax3.quiver(X, Y, U, V, M, units='x', pivot='tip', width=0.022,
...                scale=1 / 0.15)
... qk = ax3.quiverkey(Q, 0.9, 0.9, 1, r'$1 \frac{m}{s}$', labelpos='E',
...                    coordinates='figure')
... ax3.scatter(X, Y, color='0.5', s=1)
... 
... plt.show()
... 
... #############################################################################
... #
... # .. admonition:: References
... #
... #    The use of the following functions, methods, classes and modules is shown
... #    in this example:
... #
... #    - `matplotlib.axes.Axes.quiver` / `matplotlib.pyplot.quiver`
... #    - `matplotlib.axes.Axes.quiverkey` / `matplotlib.pyplot.quiverkey`
...