I am trying to plot plot a function over a 2D domain using contourf. Unfortunately, my first attempt did not work out very well. There was a region in the plot that was unexpectedly not covered by any contours. For debugging purposes, I have reduced the problem to the smallest dataset that I could find that also reveals the issue with missing filled contours:

import matplotlib.pyplot as plt
import numpy as np

v = np.array([0, 1, 2, 3])
x, y = np.meshgrid(v, v)

z = np.array([[5.5e-14, 5.5e-14, 5.5e-14, 5.5e-14],
              [2e-13, 2e-13, 2e-13, 2e-13],
              [2.2e-13, 2.2e-13, 2.2e-13, 2.2e-13],
              [0, 0,0, 0]])
fig, ax = plt.subplots()
cntr = ax.contourf(x, y, z)
fig.colorbar(cntr, ax=ax)
plt.show()

as you can see there are missing contours from y = 1.5 to approximately y = 2.0.

Another strange thing I observed: If I normalize the z matrix by multiplying by e.g. 1e14 before plotting it works fine.

Matplotlib version

• Operating system: Ubuntu 18.04
• Matplotlib version: 2.2.2 (Installed with pip)
• Matplotlib backend: TkAgg
• Python version: 3.6.1

Note: This question was first asked on stackoverflow.com: Missing filled contours when using contourf