A wide range of mathematical and physical constants are pre-defined by default. A complete list of these can be obtained by typing show variables or by consulting Chapter 3. Some of these, for example, e, pi and GoldenRatio are standard mathematical constants, the last of these being the default aspect ratio of plots produced by PyXPlot. Many of the others are physical constants, which are prefixed with phy_ to minimise clashes between their names and those of variables which the user may wish to define. Nonetheless, pre-defined constants are no different from any other variables in PyXPlot, and the user can freely re-define them.
Most of the pre-defined physical constants are not dimensionless quantities, and make use of PyXPlot’s native ability to keep track of the physical units of quantities and to convert them between different unit systems – for example, between inches and centimetres. This will be explained in more detail in Section 4.6.