poisson

lambda = 100*0.1; % rate parameter
x = 12; % particles under study
Px = poisspdf(x,lambda);% probability of exactly 12 particles
Px2 = poisscdf(x,lambda); % probability of 12 or fewer particles occuring

plot(0:1:15,poisspdf(0:1:15,lambda));
title('POISSON DISTRIBUTION');
xlabel('Number of particles under study --->');
ylabel('Probability --->');