.. _pylab_examples-multicolored_line:

pylab_examples example code: multicolored_line.py
=================================================



.. plot:: /home/mandrake/rpm/BUILD/matplotlib-1.1.1/doc/mpl_examples/pylab_examples/multicolored_line.py

::

    #!/usr/bin/env python
    '''
    Color parts of a line based on its properties, e.g., slope.
    '''
    import numpy as np
    import matplotlib.pyplot as plt
    from matplotlib.collections import LineCollection
    from matplotlib.colors import ListedColormap, BoundaryNorm
    
    x = np.linspace(0, 3 * np.pi, 500)
    y = np.sin(x)
    z = np.cos(0.5 * (x[:-1] + x[1:]))  # first derivative
    
    # Create a colormap for red, green and blue and a norm to color
    # f' < -0.5 red, f' > 0.5 blue, and the rest green
    cmap = ListedColormap(['r', 'g', 'b'])
    norm = BoundaryNorm([-1, -0.5, 0.5, 1], cmap.N)
    
    # Create a set of line segments so that we can color them individually
    # This creates the points as a N x 1 x 2 array so that we can stack points
    # together easily to get the segments. The segments array for line collection
    # needs to be numlines x points per line x 2 (x and y)
    points = np.array([x, y]).T.reshape(-1, 1, 2)
    segments = np.concatenate([points[:-1], points[1:]], axis=1)
    
    # Create the line collection object, setting the colormapping parameters.
    # Have to set the actual values used for colormapping separately.
    lc = LineCollection(segments, cmap=cmap, norm=norm)
    lc.set_array(z)
    lc.set_linewidth(3)
    
    fig1 = plt.figure()
    plt.gca().add_collection(lc)
    plt.xlim(x.min(), x.max())
    plt.ylim(-1.1, 1.1)
    
    # Now do a second plot coloring the curve using a continuous colormap
    t = np.linspace(0, 10, 200)
    x = np.cos(np.pi * t)
    y = np.sin(t)
    points = np.array([x, y]).T.reshape(-1, 1, 2)
    segments = np.concatenate([points[:-1], points[1:]], axis=1)
    
    lc = LineCollection(segments, cmap=plt.get_cmap('copper'),
        norm=plt.Normalize(0, 10))
    lc.set_array(t)
    lc.set_linewidth(3)
    
    fig2 = plt.figure()
    plt.gca().add_collection(lc)
    plt.xlim(-1, 1)
    plt.ylim(-1, 1)
    plt.show()
    

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