.. _pylab_examples-quiver_demo:

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



.. plot:: /builddir/build/BUILD/matplotlib-1.2.0/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.
    
    '''
    from pylab import *
    from numpy import ma
    
    X,Y = meshgrid( arange(0,2*pi,.2),arange(0,2*pi,.2) )
    U = cos(X)
    V = sin(Y)
    
    #1
    figure()
    Q = quiver( U, V)
    qk = quiverkey(Q, 0.5, 0.92, 2, r'$2 \frac{m}{s}$', labelpos='W',
                   fontproperties={'weight': 'bold'})
    l,r,b,t = axis()
    dx, dy = r-l, t-b
    axis([l-0.05*dx, r+0.05*dx, b-0.05*dy, t+0.05*dy])
    
    title('Minimal arguments, no kwargs')
    
    #2
    figure()
    Q = quiver( X, Y, U, V, units='width')
    qk = quiverkey(Q, 0.9, 0.95, 2, r'$2 \frac{m}{s}$',
                   labelpos='E',
                   coordinates='figure',
                   fontproperties={'weight': 'bold'})
    axis([-1, 7, -1, 7])
    title('scales with plot width, not view')
    
    #3
    figure()
    Q = quiver( X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
                pivot='mid', color='r', units='inches' )
    qk = quiverkey(Q, 0.5, 0.03, 1, r'$1 \frac{m}{s}$', fontproperties={'weight': 'bold'})
    plot( X[::3, ::3], Y[::3, ::3], 'k.')
    axis([-1, 7, -1, 7])
    title("pivot='mid'; every third arrow; units='inches'")
    
    #4
    figure()
    M = sqrt(pow(U, 2) + pow(V, 2))
    Q = quiver( X, Y, U, V, M, units='x', pivot='tip', width=0.022, scale=1/0.15)
    qk = quiverkey(Q, 0.9, 1.05, 1, r'$1 \frac{m}{s}$',
                                labelpos='E',
                                fontproperties={'weight': 'bold'})
    plot(X, Y, 'k.')
    axis([-1, 7, -1, 7])
    title("scales with x view; pivot='tip'")
    
    #5
    figure()
    Q = quiver( X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
                 color='r', units='x',
                linewidths=(2,), edgecolors=('k'), headaxislength=5 )
    qk = quiverkey(Q, 0.5, 0.03, 1, r'$1 \frac{m}{s}$', fontproperties={'weight': 'bold'})
    axis([-1, 7, -1, 7])
    title("triangular head; scale with x view; black edges")
    
    #6
    figure()
    M = 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 = quiver( U, V)
    qk = quiverkey(Q, 0.5, 0.92, 2, r'$2 \frac{m}{s}$', labelpos='W',
                   fontproperties={'weight': 'bold'})
    l,r,b,t = axis()
    dx, dy = r-l, t-b
    axis([l-0.05*dx, r+0.05*dx, b-0.05*dy, t+0.05*dy])
    title('Minimal arguments, no kwargs - masked values')
    
    
    show()
    
    

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