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.