E1 E1_sub Ei Ei_sub En En_sub Li Li_sub Spence Spence_sub

E1_sub() Sub E1_sub ( Ret As  Double, X As  Double, Optional Info As  Long  ) Exponential integral E1(x) (Subroutine version) Purpose Computes the exponential integral E1(x). E1(x) = ∫ exp(-xt)/t dt [1, ∞] = ∫ exp(-u)/u du [x, ∞] = -Ei(-x) Parameters [out] Ret Exponential integral E1(x). [in] X Argument x. (X <> 0) [out] Info (Optional) = 0: Successful exit. = 1: Floating point range error. Reference boost/math/special_functions