Can somebody help me how can I calculate a probability p from the Poisson equation (programming in R)? I know that there is the ppois function, but I'm not sure if I'm able to use it here somehow ... The equation:
Perhaps you can try uniroot
+ ppois
like below to solve p
> (p <- uniroot(function(p) ppois(5, 650 * p) - 0.5, c(0, 1), tol = 1e-10)$root)
[1] 0.008723325
and you can verify
> ppois(5, 650 * p)
[1] 0.5
or
> sum(dpois(0:5, 650*p))
[1] 0.5