Regular part

In mathematics, the regular part of a Laurent series consists of the series of terms with positive powers. That is, if

$f(z) = \sum_{n=-\infty}^{\infty} a_n (z - c)^n,$

then the regular part of this Laurent series is

$\sum_{n=0}^{\infty} a_n (z - c)^n.$

In contrast, the series of terms with negative powers is the principal part.