A note on the recursive calculation of incomplete gamma functions

  • Authors:
  • Walter Gautschi

  • Affiliations:
  • Purdue Univ., West Lafayette, IN

  • Venue:
  • ACM Transactions on Mathematical Software (TOMS)
  • Year:
  • 1999

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Abstract

It is known that the recurrence relation for incomplete gamma functions {&ggr;(a + n, x)}, 0 ≤ a n = 0, 1, 2 ..., when x is positive, is unstable—more so the larger x. Nevertheless, the recursion can be used in the range 0 ≤ n ≤ x practically without error growth, and in larger ranges 0 ≤ n ≤ N with a loss of accuracy that can be controlled by suitably limiting N.