lambda=1;
n=100;
alpha=3;
y = dgamma(n, shape=alpha, scale=lambda)

lambda = 1
n = 100
alpha = 3
y = rgamma(n, shape = alpha, scale = lambda)
hist(y, freq = FALSE, ylim=c(0,0.3))
domain = seq(from = 0, to = 8, by = 0.01)
pdf = dgamma(domain, shape = alpha, scale = lambda)
lines(density(y), col='red')
lines(domain, pdf, col='blue')