Plots to show Poisson approximation to binomial.

pois-approx-binom.R

plot_pois = function(lambda = 1.4) {
  stop_graph = max(15, ceiling(lambda + 3 * sqrt(lambda)))
  x  = 0:stop_graph
  fx = dpois(x, lambda = lambda)
  barplot(fx, names.arg = x, space = 0,
          xlab = "values", ylab = "probabilites",
          col  = "darkorange", border = "dodgerblue",
          main = "Poisson Probabilities")
}

plot_binom = function(n = 10, p = 0.5) {
  stop_graph = max(15, ceiling(n * p + 3 * sqrt(n * p)))
  x  = 0:stop_graph
  fx = dbinom(x, size = n, prob = p)
  barplot(fx, names.arg = x, space = 0,
          xlab = "values", ylab = "probabilites",
          col  = "darkorange", border = "dodgerblue",
          main = "Binomial Probabilities")
}


n = 50
p = 0.01
lambda = n * p

par(mfrow = c(2, 1))
plot_pois(lambda = lambda)
plot_binom(n = n, p = p)