[SciPy-user] noncentral F distribution?

[Neal Becker]

Robert Kern wrote:

> On Wed, May 27, 2009 at 18:47, Neal Becker <ndbecker2 at gmail.com> wrote:
> 
>> Thanks!  Just one more.  What are dfn, dfd?  The doc calls them "shape
>> parameters", but I don't know what that means.
> 
> A "shape parameter" is a generic term for any parameter that is not a
> location or scale parameter. In this case, dfn is the parameter for
> the degrees of freedom in the numerator of the expression for the F
> distribution (whether it is noncentral or not) and dfd is the degrees
> of freedom in the denominator.
> 

I think I get it now.  I had assumed that you must first construct an 
instance of a ncf object (specifying parameters) and then call the cdf 
method (specifying x).

Now I see that you simply call:

ncf.cdf (x, dfn, dfd, nc)

Is that correct?

BTW, I was confused by:

scipy.stats.ncf(momtype=1, a=None, b=None, xa=-10.0, xb=10.0, xtol=1e-14, 
badvalue=None, name=None, longname=None, shapes=None, extradoc=None)

 which is the first thing seen in the doc.  It appears to be the constructor 
declaration?  These parameters don't seem to be defined anywhere.