...one of the most highly
regarded and expertly designed C++ library projects in the
world.

— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards

#include <boost/math/special_functions/airy.hpp>

namespace boost { namespace math { template <class T>calculated-result-typeairy_bi(T x); template <class T, class Policy>calculated-result-typeairy_bi(T x, const Policy&); }} // namespaces

The function airy_bi calculates the Airy function Bi which is the second solution to the differential equation:

The final Policy argument is optional and can be used to control the behaviour of the function: how it handles errors, what level of precision to use etc. Refer to the policy documentation for more details.

The following graph illustrates how this function changes as *x*
changes: for negative *x* the function is cyclic, while
for positive *x* the value tends to infinity:

This function is implemented entirely in terms of the Bessel functions cyl_bessel_i and cyl_bessel_j - refer to those functions for detailed accuracy information.

In general though, the relative error is low (less than 100 ε) for *x
> 0* while only the absolute error is low for *x <
0* as the following error plot illustrate:

Since this function is implemented in terms of other special functions, there are only a few basic sanity checks, using test values from functions.wolfram.com.

This function is implemented in terms of the Bessel functions using the relations: