Re: [ferret_users] Statistics / student-t distribution

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi all,
Ferret does include an external function, student_t_cutoff, which may 
provide some of what you're looking for:

yes?  sh func student*
STUDENT_T_CUTOFF(P,nf)
    Return student-t cutoff
    P: Confidence Limit
    nf: nf (Number in sample)

Other statistics capabilities would be straitforward to write as 
external functions.  Our current development, PyFerret, builds Ferret as 
a Python module. This will in effect make mathematical and statistical 
functions from Python libraries available as Ferret functions.

Ansley

On 3/21/2012 8:31 AM, Paulo B. Oliveira wrote:
> One way is to use a statistical package to do the job. I ended up
> learning some R (http://www.r-project.org/) basics (the choice was
> driven by its popularity among my colleagues).
> When combined with 'littler' ( http://code.google.com/p/littler/ ) you
> can use spawn in ferret to get the simple statistics.
>
> For example, to get student-t 0.95 quantile with df-degrees of freedmon
> from ferret:
> yes? def sym df 100
> yes? let qt95 = `spawn("r -e 'cat(qt((0.95),df=($df)))'")`
>   !->  DEFINE VARIABLE qt95 = 1.66023
>
> If a long data series has to be passed on to R, it will be necessary to
> write an R script, eventually using the RNetCDF
> ( http://cran.r-project.org/web/packages/RNetCDF/index.html )
>   ncdf ( http://cran.r-project.org/web/packages/ncdf/index.html ) or
> ncdf4 (http://cran.r-project.org/web/packages/ncdf4/index.html )
> packages.
>
>
> Regards,
>
> Paulo
> ----------------------------------------------------
> On Mon, 2012-03-19 at 09:02 +0100, Hein Zelle wrote:
> > Neil Swart wrote:
> >
> > > I wondering how other Ferreters compute their statistics, and if
> > > anyone has a TINV script or similar already written?
> > I have not done this yet, but for an upcoming job I'll need to
> > determine similar bounds (quantiles) from an ensemble distribution.
> > I can do this based on the std deviation, assuming a gaussian
> > distribution, but that doesn't always hold.
> >
> > I'll be very interested to hear if it's possible to do this using
> > external functions or with different tricks.
> >
> > Kind regards,
> >       Hein Zelle