%N bessi0 %F $MIR/src/subs/bessel.for
%D Compute modified Bessel function I0
%P nebk
%: utilities, numbers
%B
      double precision function bessi0 (x)

      implicit none
      double precision x

     Compute modified Bessel function I0(x) with polynomial
     approximation.   Valid for all arguments.
     Error is < 1.6e-7 for |x|< 3.75, else < 1.9e-7

     Algorithm from Handbook of Mathematical Functions, P 378

  Input
    x       Argument
  Output
    bessi0  Result
