Procedure of ordering a product operators
This article is about rearranging a product of operators in physics. For the well-orderings on mathematical terms, see
Path ordering (term rewriting).
In theoretical physics, path-ordering is the procedure (or a meta-operator ) that orders a product of operators according to the value of a chosen parameter:
Here p is a permutation that orders the parameters by value:
For example:
In many fields of physics, the most common type of path-ordering is time-ordering, which is discussed in detail below.