.. _images_contours_and_fields-streamplot_demo_masking:

images_contours_and_fields example code: streamplot_demo_masking.py
===================================================================



.. plot:: /home/tcaswell/source/p/matplotlib/doc/mpl_examples/images_contours_and_fields/streamplot_demo_masking.py

::

    """
    Demo of the streamplot function with masking.
    
    This example shows how streamlines created by the streamplot function skips
    masked regions and NaN values.
    """
    import numpy as np
    import matplotlib.pyplot as plt
    
    w = 3
    Y, X = np.mgrid[-w:w:100j, -w:w:100j]
    U = -1 - X**2 + Y
    V = 1 + X - Y**2
    speed = np.sqrt(U*U + V*V)
    
    mask = np.zeros(U.shape, dtype=bool)
    mask[40:60, 40:60] = True
    U[:20, :20] = np.nan
    U = np.ma.array(U, mask=mask)
    
    fig, ax = plt.subplots()
    ax.streamplot(X, Y, U, V, color='r')
    
    ax.imshow(~mask, extent=(-w, w, -w, w), alpha=0.5,
              interpolation='nearest', cmap=plt.cm.gray)
    
    plt.show()
    

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