WE_1 WEi WEn WLi WSpence

WE_1() Function WE_1 ( X As  Double ) Exponential integral E1(x) Purpose WE_1 computes the exponential integral E1(x) for positive argument x and the Cauchy principal value for negative x. E1(x) = ∫ exp(-xt)/t dt [1, ∞] = ∫ exp(-u)/u du [x, ∞] = -Ei(-x) Returns Exponential integral E1(x). Parameters [in] X Argument x. (X <> 0) Reference boost/math/special_functions