In mathematics, the regular part of a Laurent series consists of the series of terms with positive powers. That is, if
f ( z ) = ∑ n = − ∞ ∞ a n ( z − c ) n , {\displaystyle f(z)=\sum _{n=-\infty }^{\infty }a_{n}(z-c)^{n},}
then the regular part of this Laurent series is
∑ n = 0 ∞ a n ( z − c ) n . {\displaystyle \sum _{n=0}^{\infty }a_{n}(z-c)^{n}.}
In contrast, the series of terms with negative powers is the principal part.
References