I've come across several approximations for Mills ratio, but I haven't found any good ones for the Inverse Mills ratio. Is there any known closed-form approximation for the Inverse Mills ratio (link) specifically for a normal random variable, denoted as $\frac{\phi(x)}{\Phi(x)}$ for "$x>0$"? (ratio of normal pdf to normal cdf)
I am expecting to have closed form expression for positive arguments.
