chi ci shi si

ci() double ci ( double  x ) Cosine integral Ci(x) Purpose ci computes the cosine integral. Ci(x) = -∫ cos(t)/t dt [x, ∞] Returns Cosine integral Ci(x). Parameters [in] x Argument x. (x != 0) (If x < 0, returns the real part = Ci(|x|)) Error handling If x = 0, -inf is returned and range error (ERANGE) occurs. Other range error (ERANGE) may occur.