Complementary error function
= Complementary error function
{title2=$\operatorname{erfc}z=1-\operatorname{erf}z$}
The complementary <error function> avoids subtracting a quantity close to one when describing a small <Gaussian integral> tail. For real $x>0$, $\operatorname{erfc}x=(2/\sqrt\pi)\int_x^\infty e^{-t^2}\,dt$; <analytic continuation> defines it for complex arguments.