Plotting the Gamma Distribution in Splus

1998-09-23

The function pldg(alpha) plots the gamma distribtion with shape parameter alpha; I have set the scale parameter equal to the shape parameter so the mean is always 1 and the graphs remain comparable as alpha changes.

> pldg
function(al = 2)
{
        xx <- seq(0, 5, 0.05)
        plot(xx, dgamma(xx * al, al) * al, type = "l")
}

The function pldgm() applies pldg() to an array of alpha values.

 
> pldgm
function(al = 2)
{
        sapply(al, pldg)
        NULL
}

Hence calling pldgm with an increasing sequence of values like

pldgm(seq(.1, 30, .2))

gives a "movie" showing the convergence from a J-shaped distribution to normality as the shape parameter increases.

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