Matplotlib 2.x By Example

Symmetrical logarithmic scale

The logarithmic scale described in the previous section supports positive numbers only. Suppose y = ab, where a is positive; y must be also positive if b equals to any real number (positive, negative, whole numbers, and decimal numbers). When y approaches zero, the limit of the base a logarithm of y is minus infinity. Meanwhile, the base a logarithm of a negative number is undefined. If we try to supply non-positive numbers (≤0) to numpy.log(), we see the following errors:

import numpy as npnp.log(0)# Output: -infnp.log(-1)# Output: nan

Matplotlib provides three ways to address non-positive numbers in a logarithmic scale.

Firstly, Matplotlib can mask non-positive values as invalid. This is equivalent to specifying ...