j0, j1, jn, y0, y1, yn - bessel functions

 #include <math.h> 

 double j0(x)  double x; 

 double j1(x)  double x; 

 double jn(n, x)  double x; 

 double y0(x)  double x; 

 double y1(x)  double x; 

 double yn(n, x)  double x; 

These functions calculate Bessel functions of the first and second kinds for real arguments and integer orders. intro(3M) Negative arguments cause y0, y1, and yn to return a huge negative value and set errno to EDOM.