.. _pylab_examples-quiver_demo:

pylab_examples example code: quiver_demo.py
===========================================



.. plot:: /home/tcaswell/src/p/matplotlib/doc/mpl_examples/pylab_examples/quiver_demo.py

::

    '''
    ========================================================
    Demonstration of advanced quiver and quiverkey functions
    ========================================================
    
    Known problem: the plot autoscaling does not take into account
    the arrows, so those on the boundaries are often out of the picture.
    This is *not* an easy problem to solve in a perfectly general way.
    The workaround is to manually expand the axes.
    '''
    import matplotlib.pyplot as plt
    import numpy as np
    from numpy import ma
    
    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)
    
    plt.figure()
    plt.title('Arrows scale with plot width, not view')
    Q = plt.quiver(X, Y, U, V, units='width')
    qk = plt.quiverkey(Q, 0.9, 0.9, 2, r'$2 \frac{m}{s}$', labelpos='E',
                       coordinates='figure')
    
    plt.figure()
    plt.title("pivot='mid'; every third arrow; units='inches'")
    Q = plt.quiver(X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
                   pivot='mid', units='inches')
    qk = plt.quiverkey(Q, 0.9, 0.9, 1, r'$1 \frac{m}{s}$', labelpos='E',
                       coordinates='figure')
    plt.scatter(X[::3, ::3], Y[::3, ::3], color='r', s=5)
    
    plt.figure()
    plt.title("pivot='tip'; scales with x view")
    M = np.hypot(U, V)
    Q = plt.quiver(X, Y, U, V, M, units='x', pivot='tip', width=0.022,
                   scale=1 / 0.15)
    qk = plt.quiverkey(Q, 0.9, 0.9, 1, r'$1 \frac{m}{s}$', labelpos='E',
                       coordinates='figure')
    plt.scatter(X, Y, color='k', s=5)
    
    plt.show()
    

Keywords: python, matplotlib, pylab, example, codex (see :ref:`how-to-search-examples`)