You are reading an old version of the documentation (v1.4.3). For the latest version see

We're updating the default styles for Matplotlib 2.0

Learn what to expect in the new updates


Previous topic

pylab_examples example code:

Next topic

pylab_examples example code:

This Page

pylab_examples example code: multicolored_line.pyΒΆ

(Source code)

#!/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)

fig1 = plt.figure()
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))

fig2 = plt.figure()
plt.xlim(-1, 1)
plt.ylim(-1, 1)

Keywords: python, matplotlib, pylab, example, codex (see Search examples)