besselJ0 beta combination factorial result

double special_functions::beta ( const double  x, const double  y  ) Function that computes the beta function. Author: Rochan R. Upadhyay Parameters: x : First parameter of Beta function. y : Second parameter of Beta function. From GSL manual : These routines compute the Beta Function, B(a,b) = Gamma(a)Gamma(b)/Gamma(a+b) subject to a and b not being negative integers. Date: 10/12/2010