acosh.hpp

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#ifndef STAN__AGRAD__REV__FUNCTIONS__ACOSH_HPP
#define STAN__AGRAD__REV__FUNCTIONS__ACOSH_HPP

#include <math.h>
#include <stan/agrad/rev/var.hpp>
#include <stan/agrad/rev/internal/v_vari.hpp>
#include <boost/math/special_functions/fpclassify.hpp>
#include <stan/agrad/rev/numeric_limits.hpp>
#include <stan/agrad/rev/operators/operator_greater_than.hpp>
#include <stan/agrad/rev/operators/operator_equal.hpp>
#include <stan/agrad/rev/operators/operator_unary_negative.hpp>

namespace stan {
  namespace agrad {

    namespace {
      class acosh_vari : public op_v_vari {
      public:
        acosh_vari(double val, vari* avi) :
          op_v_vari(val,avi) {
        }
        void chain() {
          avi_->adj_ += adj_ / std::sqrt(avi_->val_ * avi_->val_ - 1.0);
        }
      };
    }

    inline var acosh(const stan::agrad::var& a) {
      if (boost::math::isinf(a.val()) && a > 0.0)
        return var(new acosh_vari(a.val(),a.vi_));
      return var(new acosh_vari(::acosh(a.val()),a.vi_));
    }

  }
}

#endif