.. _pylab_examples-quiver_demo:

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



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

::

    '''
    Demonstration of quiver and quiverkey functions. This is using the
    new version coming from the code in quiver.py.
    
    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)
    
    # 1
    plt.figure()
    Q = plt.quiver(U, V)
    qk = plt.quiverkey(Q, 0.5, 0.92, 2, r'$2 \frac{m}{s}$', labelpos='W',
                       fontproperties={'weight': 'bold'})
    l, r, b, t = plt.axis()
    dx, dy = r - l, t - b
    plt.axis([l - 0.05*dx, r + 0.05*dx, b - 0.05*dy, t + 0.05*dy])
    
    plt.title('Minimal arguments, no kwargs')
    
    # 2
    plt.figure()
    Q = plt.quiver(X, Y, U, V, units='width')
    qk = plt.quiverkey(Q, 0.9, 0.95, 2, r'$2 \frac{m}{s}$',
                       labelpos='E',
                       coordinates='figure',
                       fontproperties={'weight': 'bold'})
    plt.axis([-1, 7, -1, 7])
    plt.title('scales with plot width, not view')
    
    # 3
    plt.figure()
    Q = plt.quiver(X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
                   pivot='mid', color='r', units='inches')
    qk = plt.quiverkey(Q, 0.5, 0.03, 1, r'$1 \frac{m}{s}$',
                       fontproperties={'weight': 'bold'})
    plt.plot(X[::3, ::3], Y[::3, ::3], 'k.')
    plt.axis([-1, 7, -1, 7])
    plt.title("pivot='mid'; every third arrow; units='inches'")
    
    # 4
    plt.figure()
    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, 1.05, 1, r'$1 \frac{m}{s}$',
                       labelpos='E',
                       fontproperties={'weight': 'bold'})
    plt.plot(X, Y, 'k.')
    plt.axis([-1, 7, -1, 7])
    plt.title("scales with x view; pivot='tip'")
    
    # 5
    plt.figure()
    Q = plt.quiver(X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
                   color='r', units='x',
                   linewidths=(2,), edgecolors=('k'), headaxislength=5)
    qk = plt.quiverkey(Q, 0.5, 0.03, 1, r'$1 \frac{m}{s}$',
                       fontproperties={'weight': 'bold'})
    plt.axis([-1, 7, -1, 7])
    plt.title("triangular head; scale with x view; black edges")
    
    # 6
    plt.figure()
    M = np.zeros(U.shape, dtype='bool')
    M[U.shape[0]/3:2*U.shape[0]/3,
      U.shape[1]/3:2*U.shape[1]/3] = True
    U = ma.masked_array(U, mask=M)
    V = ma.masked_array(V, mask=M)
    Q = plt.quiver(U, V)
    qk = plt.quiverkey(Q, 0.5, 0.92, 2, r'$2 \frac{m}{s}$', labelpos='W',
                       fontproperties={'weight': 'bold'})
    l, r, b, t = plt.axis()
    dx, dy = r - l, t - b
    plt.axis([l - 0.05 * dx, r + 0.05 * dx, b - 0.05 * dy, t + 0.05 * dy])
    plt.title('Minimal arguments, no kwargs - masked values')
    
    
    plt.show()
    

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