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#include <boost/math/special_functions/acosh.hpp>

template<class T> 
calculated-result-type acosh(const T x);

template<class T, class Policy> 
calculated-result-type acosh(const T x, const Policy&);

Computes the reciprocal of (the restriction to the range of [0;+∞[) the hyperbolic cosine function, at x. Values returned are positive. Generalised Taylor series are used near 1 and Laurent series are used near the infinity to ensure accuracy.

If x is in the range ]-∞;+1[ then returns the result of domain_error.

The return type of this function is computed using the result type calculation rules: the return type is double when T is an integer type, and T otherwise.

The final Policy argument is optional and can be used to control the behaviour of the function: how it handles errors, what level of precision to use etc. Refer to the policy documentation for more details.