WE_1 WEi WEn WLi WSpence

WEi() Function WEi ( X As  Double ) Exponential integral Ei(x) Purpose WEi computes the exponential integral Ei(x) for negative argument x and the Cauchy principal value for positive x. Ei(x) = -∫ exp(-t)/t dt [-x, ∞] = -E1(-x) Returns Exponential integral Ei(x). Parameters [in] X Argument x. (X <> 0) Reference boost/math/special_functions