_cos_pi _powm1 _sin_pi _sqrt1pm1

_powm1() double _powm1 ( double  x, double  y  ) x^y - 1 Purpose powm1 evaluates x^y - 1 accurately in the sense of relative error when y is very small or x is close to 1. Returns x^y - 1. Parameters [in] x Argument x. [in] y Argument y. Error handling Range error (ERANGE) may occur. Reference boost/math/special_functions