//  (C) Copyright John Maddock 2005.

 //  Use, modification and distribution are subject to the

 //  Boost Software License, Version 1.0. (See accompanying file

 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

 #ifndef BOOST_MATH_COMPLEX_ACOSH_INCLUDED

 #define BOOST_MATH_COMPLEX_ACOSH_INCLUDED

 #ifndef BOOST_MATH_COMPLEX_DETAILS_INCLUDED

 #  include <boost/math/complex/details.hpp>

 #endif

 #ifndef BOOST_MATH_COMPLEX_ATANH_INCLUDED

 #  include <boost/math/complex/acos.hpp>

 #endif

 namespace boost{ namespace math{

 template<class T> 

 inline std::complex<T> acosh(const std::complex<T>& z)

 {

    //

    // We use the relation acosh(z) = +-i acos(z)

    // Choosing the sign of multiplier to give real(acosh(z)) >= 0

    // as well as compatibility with C99.

    //

    std::complex<T> result = boost::math::acos(z);

    if(!detail::test_is_nan(result.imag()) && result.imag() <= 0)

       return detail::mult_i(result);

    return detail::mult_minus_i(result);

 }

 } } // namespaces

 #endif // BOOST_MATH_COMPLEX_ACOSH_INCLUDED