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# st: Fuction Fden Help

 From Bryan Griffin To statalist@hsphsun2.harvard.edu Subject st: Fuction Fden Help Date Mon, 5 Mar 2012 13:05:12 -0500

```Hi --

I would like to create a plot showing density of F distribution for various
degrees of freedom, but I'm having difficulty getting this to work. I was
not able to find an example for the F distribution in the archives or on
the net, but I found this example which works well for the normal
distribution:

graph twoway function normden(x, 0, 1) , range(-5 5)

So using that as an example, I tried a number of variations of this

twoway function Fden(3,20,1)

No matter what numbers I place within the Fden() function the returned
graph is a flat line.

I also tried specifying a range, like this

twoway function Fden(3,20,1), range(.1 100)

but, again, no matter which numbers I try the graph returns a flat line.

Any suggestions?

Thanks,
Bryan

P.S. Here's the Function help information:

Title

[D] functions -- Functions

Probability density function

Fden(n1,n2,f)
Domain n1:    1e-323 to 8e+307 (may be nonintegral)
Domain n2:    1e-323 to 8e+307 (may be nonintegral)
Domain f:     -8e+307 to 8e+307
Interesting domain is f > 0
Range:        0 to 8e+307
Description:  returns the probability density function for the F
distribution with n1 numerator and n2 denominator degrees of freedom.
returns 0 if f < 0.
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```