Editing Characteristic polynomial (section)

==Secular function and secular equation==

===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.

===Secular equation===
''Secular equation'' may have several meanings.

* In [[linear algebra]] it is sometimes used in place of characteristic equation.
* In [[astronomy]] it is the algebraic or numerical expression of the magnitude of the inequalities in a planet's motion that remain after the inequalities of a short period have been allowed for.<ref>{{cite web
| url = http://dict.die.net/secular%20equation/
| title = secular equation
|access-date = January 21, 2010}}</ref>

* In [[molecular orbital]] calculations relating to the energy of the electron and its wave function it is also used instead of the characteristic equation.