绘制伽玛概率密度函数

Question

I'm trying to plot the gamma probability density function in R where y∈(0,10) for (k = 1,μ = 1), (k = 2, μ = 1), (k = 2, μ = 2). In R,

In R, the pgamma function accepts:

pgamma(q, shape, rate = 1, scale = 1/rate, alpha = shape, beta = scale, lower.tail = TRUE, log.p = FALSE)

In R, i tried:

pgamma(1,1,rate=1,scale = 1/rate, alpha = shape, beta = scale, lower.tail = True, log.p = False)

But i get the message

Error in pgamma(1, 1, rate = 1, scale = 1/rate, lower.tail = TRUE, log.p = FALSE) : 
object 'rate' not found

It's my first time plotting a gamma distribution and would appreciate some help on this.

Answer 1

The following plots the three densities using base R graphics.

First, the parameter values you want. I am assuming your mu is as defined in the Wikipedia page of the Gamma distribution .

k <- c(1, 2, 2)
mu <- c(1, 1, 2)
theta <- mu/k

Now, the plots.

plot(0, 0, xlim = c(0, 10), ylim = c(0, 1), type = "n")
for(i in seq_along(k))
  curve(dgamma(x, shape = k[i], scale = theta[i]), from = 0, to = 10, col = i, add = TRUE)