constants.hpp

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#ifndef STAN__MATH__CONSTANTS_HPP
#define STAN__MATH__CONSTANTS_HPP

#include <boost/math/constants/constants.hpp>

namespace stan {

  namespace math {

    const double E = boost::math::constants::e<double>();

    const double SQRT_2 = std::sqrt(2.0);

    const double INV_SQRT_2 = 1.0 / SQRT_2;

    const double LOG_2 = std::log(2.0);

    const double LOG_10 = std::log(10.0);

    const double INFTY = std::numeric_limits<double>::infinity();

    const double NEGATIVE_INFTY = - std::numeric_limits<double>::infinity();

    const double NOT_A_NUMBER = std::numeric_limits<double>::quiet_NaN();
    
    const double EPSILON = std::numeric_limits<double>::epsilon();

    const double NEGATIVE_EPSILON = - std::numeric_limits<double>::epsilon();


    /*
     * Log pi divided by 4
     * \f$ \log \pi / 4 \f$
     */
    const double LOG_PI_OVER_FOUR = std::log(boost::math::constants::pi<double>()) / 4.0;

    inline double pi() {
      return boost::math::constants::pi<double>();
    }

    inline double e() {
      return E;
    }

    inline double sqrt2() {
      return SQRT_2;
    }


    inline double log10() {
      return LOG_10;
    }

    inline double positive_infinity() {
      return INFTY;
    }

    inline double negative_infinity() {
      return NEGATIVE_INFTY;
    }

    inline double not_a_number() {
      return NOT_A_NUMBER;
    }

    inline double machine_precision() {
      return EPSILON;
    }

    const double TWO_OVER_SQRT_PI = 2.0 / std::sqrt(boost::math::constants::pi<double>());
    
    const double NEG_TWO_OVER_SQRT_PI = -TWO_OVER_SQRT_PI;
    
    const double INV_SQRT_TWO_PI = 1.0 / std::sqrt(2.0 * boost::math::constants::pi<double>());
    
  }
}

#endif