Editing Path-ordering (section)

== Examples ==

If an [[operator (physics)|operator]] is not simply expressed as a product, but as a function of another operator, we must first perform a [[Taylor expansion]] of this function. This is the case of the [[Wilson loop]], which is defined as a [[path-ordered exponential]] to guarantee that the Wilson loop encodes the [[holonomy]] of the [[gauge connection]]. The parameter ''σ'' that determines the ordering is a parameter describing the [[contour integration|contour]], and because the contour is closed, the Wilson loop must be defined as a [[trace (linear algebra)|trace]] in order to be [[gauge-invariant]].