poisson.py

''' Probability mass function of a Poisson random variable, differing λ values '''

from IPython.core.pylabtools import figsize
from matplotlib import pyplot as plt
import scipy.stats as stats
import numpy as np

a = np.arange(16)
poi = stats.poisson
lambda_ = [1.5, 4.25]
colors = ['#348ABD', '#A60628']

plt.bar(a, poi.pmf(a, lambda_[0]), color=colors[0],
       label="$\lambda = %.1f$" % lambda_[0], alpha=0.60,
       edgecolor=colors[0], lw="3")

plt.bar(a, poi.pmf(a, lambda_[1]), color=colors[1],
       label="$\lambda = %.1f$" % lambda_[1], alpha=0.60,
       edgecolor=colors[1], lw="3")

plt.xticks(a + 0.4, a)
plt.legend()
plt.ylabel("Probability of $k$")
plt.xlabel("$k$")
plt.title("Probability mass function of a Poisson random variable, differing λ values")

plt.show()