BESSELY(x,order) returns the Bessel function of the second kind at x for the specified order. The Bessel functions of the second kind are defined as the solutions to the Bessel differential equation
which are singular at the origin.
The n-th order Bessel function of x is:
where J denotes the Bessel function of the first kind.
The plot below shows the Bessel function for n=0,1,2,3,4,5.
Order must be greater than or equal to 0. If order is not an integer, it is truncated. x must be greater than or equal to 0.
For more information on the Bessel function see the reference at MathWorld