e1 ei li

e1() function e1 ( x::Real  ) Exponential integral E1(x) Purpose e1 computes the exponential integral E1(x) for the argument x. E1(x) = ∫ exp(-xt)/t dt [1, ∞] = ∫ exp(-u)/u du [x, ∞] = -Ei(-x) Returns Float64 Exponential integral E1(x). Parameters [in] x Argument x. (x != 0) Error handling If x = 0, inf is returned and range error (ERANGE) occurs. Other range error (ERANGE) may occur. Reference boost/math/special_functions