log_diff_exp.hpp

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#ifndef STAN__MATH__FUNCTIONS__LOG_DIFF_EXP_HPP
#define STAN__MATH__FUNCTIONS__LOG_DIFF_EXP_HPP

#include <boost/math/tools/promotion.hpp>
#include <stdexcept>
#include <boost/throw_exception.hpp>
#include <stan/math/functions/log1m_exp.hpp>

namespace stan {
  namespace math {

    template <typename T1, typename T2>
    inline typename boost::math::tools::promote_args<T1,T2>::type
    log_diff_exp(const T1 x, const T2 y) {
      if (x <= y)
        return std::numeric_limits<double>::quiet_NaN();
      return x + log1m_exp(y - x);
    }

  }
}

#endif