incomplete Bessel function



 Hello,
 I need to calculate the incomplete Bessel function.
 The form of this function is defined by the formula
                 inf
   K  (x,y) = int   exp(-(xt+(y/t))) * (t**(n-1)) dt
    n            1
 with x and y .gt. 0 and arbitrary n.
 More particularly, I have to evaluate this for n=0.
 Does anybody have any information on the availability
 of algorithm(s) for this.
 Thanks in advance.
 Isabelle Flamant