The topic is the inverse problem for gamma distribution, i.e., for given and , to find x such that
The author gives an algorithm and its FORTRAN program. The method is to solve the equation with a combination of the third-order Schröder iteration and the Newton-Raphson method. The initial value is given by the Wilson-Hilferty transformation (subroutine WILSON), and the incomplete gamma function (subroutine GAMAIN) is computed by using the algorithm of Moore [Algorithm AS187; Applied statistics 31(3), 330 (1982)]. The author shows an application example on the annual peak discharges of a water-fall, which gives a nice numerical result in few iterations.