First, n values gi were drawn from a gamma distribution with mean m and dispersion parameter k. Second, each of these values was used as the intensity parameter for a Poisson random variate to yield a NB-distributed value xi, i.e. xi = Poisson(gi).

不太懂如何在R中产生上述随机数，dispersion parameter 怎么在R中体现呢？？？谢谢大家，感激不尽