?===================================================================

? Program to compute and plot Poisson and negative binomial        =

? probabilities. User sets ALPHAI and LAMBDAI then executes.       =

?===================================================================

PROCEDURE

  SAMPLE              ; 1 - 36$

  CREATE              ; i = trn(0,1)$

  CALC                ; thetai  = 1/alphai$

  SAMPLE              ; 1$

  CREATE              ; logpp   = -lambdai

                      ; logpn   = thetai*log(thetai/(thetai+lambdai))$

  SAMPLE              ; 2 - 51$

  CREATE              ; logpp = log(lambdai)-log(i)+logpp[-1]

                      ; logpn = log(lambdai/(thetai+lambdai))

                               +log(thetai+i-1)-log(i)+logpn[-1]$

  SAMPLE              ; 1 - 36$

  CREATE              ; pp = exp(logpp)

                      ; pn = exp(logpn)$

  PLOT                ; lhs=i;rhs=pp,pn;fill$

ENDPROC

?

? Set desired values of lambda and alpha.

?

CALC                ; lambdai = 10

                    ; alphai  = .2

EXECUTE