Matplotlib plot with variable line width

Question

Is it possible to plot a line with variable line width in matplotlib? For example:

from pylab import *
x = [1, 2, 3, 4, 5]
y = [1, 2, 2, 0, 0]
width = [.5, 1, 1.5, .75, .75]

plot(x, y, linewidth=width)

This doesn't work because linewidth expects a scalar.

Note: I'm aware of *fill_between()* and *fill_betweenx()*. Because these only fill in x or y direction, these do not do justice to cases where you have a slanted line. It is desirable for the fill to always be normal to the line. That is why a variable width line is sought.

Answer 1

Use LineCollections. A way to do it along the lines of this Matplotlib example is

import numpy as np from matplotlib.collections import LineCollection import matplotlib.pyplot as plt x = np.linspace(0,4*np.pi,10000) y = np.cos(x) lwidths=1+x[:-1] points = np.array([x, y]).T.reshape(-1, 1, 2) segments = np.concatenate([points[:-1], points[1:]], axis=1) lc = LineCollection(segments, linewidths=lwidths,color='blue') fig,a = plt.subplots() a.add_collection(lc) a.set_xlim(0,4*np.pi) a.set_ylim(-1.1,1.1) fig.show() 

Answer 2

An alternative to Giulio Ghirardo's answer which divides the lines in segments you can use matplotlib's in-built scatter function which construct the line by using circles instead:

from matplotlib import pyplot as plt import numpy as np  x = np.linspace(0,10,10000) y = 2 - 0.5*np.abs(x-4) lwidths = (1+x)**2 # scatter 'o' marker size is specified by area not radius  plt.scatter(x,y, s=lwidths, color='blue') plt.xlim(0,9) plt.ylim(0,2.1) plt.show() 

In my experience I have found two problems with dividing the line into segments:

1. For some reason the segments are always divided by very thin white lines. The colors of these lines get blended with the colors of the segments when using a very large amount of segments. Because of this the color of the line is not the same as the intended one.

2. It doesn't handle very well very sharp discontinuities.