Compute the discrete Weibull cumulative distribution function.
with q and denoting the shape parameters.
DIWHAZ = Compute the discrete Weibull hazard function.
DIWPDF = Compute the discrete Weibull probability mass function.
DIWPPF = Compute the discrete Weibull percent point function.
Johnson, Kemp, and Kotz (2005), "Univariate Discrete Distributions", Third Edition, Wiley, pp. 510-511.
Nakagawa and Osaki (1975), "The Discrete Weibull Distribution", IEEE Transactions on Reliability, R-24, pp. 300-301.