E1 Ei En Li Spence

Ei() Function Ei ( X As  Double, Optional Info As  Long  ) Exponential integral Ei(x) Purpose This routine computes the exponential integral Ei(x) for the argument x. Ei(x) = -integral of exp(-t)/t dt [-x, inf] = -E1(-x) Returns Double Exponential integral Ei(x). Parameters [in] X Argument x. (X <> 0) [out] Info (Optional) = 0: Successful exit. = 1: Floating point range error. Reference boost/math/special_functions