view release on metacpan or  search on metacpan

src/boost/math/special_functions/detail/bessel_j0.hpp  view on Meta::CPAN

    static const T QS[] = {
         static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 5.7105024128512061905e+03)),
         static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.1951131543434613647e+04)),
         static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 7.2642780169211018836e+03)),
         static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.4887231232283756582e+03)),
         static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 9.0593769594993125859e+01)),
         static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.0))
    };
    static const T x1  =  static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.4048255576957727686e+00)),
                   x2  =  static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 5.5200781102863106496e+00)),
                   x11 =  static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 6.160e+02)),
                   x12 =  static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.42444230422723137837e-03)),
                   x21 =  static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.4130e+03)),
                   x22 =  static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 5.46860286310649596604e-04));

    T value, factor, r, rc, rs;

    BOOST_MATH_STD_USING
    using namespace boost::math::tools;
    using namespace boost::math::constants;

    if (x < 0)
    {
        x = -x;                         // even function
    }
    if (x == 0)
    {
        return static_cast<T>(1);
    }
    if (x <= 4)                       // x in (0, 4]
    {
        T y = x * x;
        BOOST_ASSERT(sizeof(P1) == sizeof(Q1));
        r = evaluate_rational(P1, Q1, y);
        factor = (x + x1) * ((x - x11/256) - x12);
        value = factor * r;
    }
    else if (x <= 8.0)                  // x in (4, 8]
    {
        T y = 1 - (x * x)/64;
        BOOST_ASSERT(sizeof(P2) == sizeof(Q2));
        r = evaluate_rational(P2, Q2, y);
        factor = (x + x2) * ((x - x21/256) - x22);
        value = factor * r;
    }
    else                                // x in (8, \infty)
    {
        T y = 8 / x;
        T y2 = y * y;
        BOOST_ASSERT(sizeof(PC) == sizeof(QC));
        BOOST_ASSERT(sizeof(PS) == sizeof(QS));
        rc = evaluate_rational(PC, QC, y2);
        rs = evaluate_rational(PS, QS, y2);
        factor = sqrt(2 / (x * pi<T>()));
        //
        // What follows is really just:
        //
        // T z = x - pi/4;
        // value = factor * (rc * cos(z) - y * rs * sin(z));
        //
        // But using the addition formulae for sin and cos, plus
        // the special values for sin/cos of pi/4.
        //
        T sx = sin(x);
        T cx = cos(x);
        value = factor * (rc * (cx * constants::one_div_root_two<T>() + sx * constants::half_root_two<T>()) 
           - y * rs * (sx * constants::one_div_root_two<T>() - cx * constants::half_root_two<T>()));
    }

    return value;
}

}}} // namespaces

#endif // BOOST_MATH_BESSEL_J0_HPP