Sigmoid functions for the smooth approximation to the absolute value function

Abstract

We present smooth approximations to the absolute value function |x| using sigmoid functions. In particular, x erf(x/μ) is proved to be a better smooth approximation for |x| than x tanh(x/μ) and x2+μ {{x2} + μ with respect to accuracy. To accomplish our goal we also provide sharp hyperbolic bounds for the error function.