#include <math.h> double j0(double x); double j1(double x); double jn(int n, double x); double y0(double x); double y1(double x); double yn(int n, double x);
The y0() and y1() functions return Bessel functions of x of the second kind of orders 0 and 1, respectively. The yn() function returns the Bessel function of x of the second kind of order n.
For the functions y0(), y1() and yn(), the value of x must be positive. For negative values of x, these functions return -HUGE_VAL.