nag_incomplete_gamma (s14bac) Example Program Results
        a           x           p           q
      2.0000      3.0000      0.8009      0.1991
      7.0000      1.0000      0.0001      0.9999
      0.5000     99.0000      1.0000      0.0000
     20.0000     21.0000      0.6157      0.3843
     21.0000     20.0000      0.4409      0.5591