Principal argument
= Principal argument
{title2=$\operatorname{Arg}z\in(-\pi,\pi]$}
The <principal argument> selects a single <complex argument> of a nonzero <complex number>, conventionally in $(-\pi,\pi]$. It is the <imaginary part> of the <principal logarithm>. The alternative interval $[-\pi,\pi)$ changes the convention on the negative <real axis>. Neither convention makes the selected <complex argument> continuous across that axis.