6.4.10. Inverse hyperbolic
functions (acosh, asinh, atanh)
These functions are the inverses of the ISO-required cosh, sinh and tanh.
double acosh(double x);
double asinh(double x);
double atanh(double x);
Here:
acosh always
has a choice of two return values, one positive and one negative, because cosh is
a symmetric function (that is, it returns the same value when applied
to x or –x
acosh returns an EDOM error
if called with an argument less than 1.0.
atanh returns an EDOM error
if called with an argument whose absolute value exceeds 1.0.
PDF version