convention about the definition of the principal value, sometimes its
                values
                are supposed to be in the interval $[0, 2\pi).$ This ambiguity is a perpetual source of
                misunderstandings and errors.</p>




            <hr>



            <p>The principal value $\textbf{Arg}(z)$ of a complex number $z=x+iy$ is normally given by
                $$\Theta=\arctan\left(\frac{y}{x}\right),$$
                where $y/x$ is the slope, and $\arctan$ converts slope to angl