A regular perturbation is a method in perturbation theory for a problem depending on a small parameter 
. It seeks the solution as an asymptotic series, commonly a power
series expansion
 |
whose successive terms remain valid throughout the domain of interest as 
.
Setting 
leaves the type, order, and number of conditions of the original problem unchanged,
and the correction terms are ordinarily found from a sequence of problems of the
same general kind. This contrasts with a singular
perturbation, for which the limiting problem changes character and the series
expansion is generally not uniform.
