Algorithm 926
Ian B. Thompson · ACM Transactions on Mathematical Software · 2013
An algorithm for accurately computing the lower incomplete gamma function γ ( a , t ) in the case where a = n + 1/2, n ∈ Z and t < 0 is described. Series expansions and analytic continuation are employed to compute the function for certain critical values of n , and these results are used to initiate stable recurrence. The algorithm has been implemented in Fortran 2003, with precompuations carried out in Maple.