R rnegbin

[TheSeqGeek]

Anyone know what is the explicit function that is being plotted when rnegbin is called i.e. what is the exact function for negative binomial?

For example using these numbers

plot(rnegbin(1000, 45, 5))

[dariober]

what is the exact function for negative binomial?

From the help of rnegbin:

The function uses the representation of the Negative Binomial
distribution as a continuous mixture of Poisson distributions with
Gamma distributed means

and from the code itself:

rpois(k, (mu * rgamma(k, theta))/theta)

[Michael.Ante]

rnegbin is a function which generates values according to a Negative Binomial distribution. The result of your example generates a vector of 1000 values.
Please use the R help function for more information.
Moreover, just typing the function name gives you:

> rnegbin
function (n, mu = n, theta = stop("'theta' must be specified"))
{   
    k <- if (length(n) > 1L)
        length(n)
    else n
    rpois(k, (mu * rgamma(k, theta))/theta)
}

The plot function is just plot.default with your 1000 values on the y-axis and each values rank in the vector on the x-axis.

[TheSeqGeek]

I guess I was more looking for f(x) = e^(lambda) bla bla bla

[dpryan]

It'd be the probability mass function, which you can find on wikipedia.

[TheSeqGeek]

Thank you.... I looked on Wikipedia and didn't know which one of those... PMF will do

Thanks