Editing Characteristic polynomial (section)

===Secular function===

The term '''secular function''' has been used for what is now called ''characteristic polynomial'' (in some literature the term secular function is still used). The term comes from the fact that the characteristic polynomial was used to calculate [[Secular phenomena|secular perturbations]] (on a time scale of a century, that is, slow compared to annual motion) of planetary orbits, according to [[Joseph Louis Lagrange|Lagrange]]'s theory of oscillations.