Regular part

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

$f(z)=\sum _{n=-\mathrm{\infty }}^{\mathrm{\infty }}{a}_n(z-c{)}^n,$

then the regular part of this Laurent series is

$\sum _{n=0}^{\mathrm{\infty }}{a}_n(z-c{)}^n.$

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