[SciPy-Dev] Working on the docstring for stats.distributions.rv_continuous.fit

David Goldsmith d.l.goldsmith@gmail....
Wed Jun 16 11:18:01 CDT 2010


On Wed, Jun 16, 2010 at 8:59 AM, Skipper Seabold <jsseabold@gmail.com>wrote:

> On Wed, Jun 16, 2010 at 11:49 AM, David Goldsmith
> <d.l.goldsmith@gmail.com> wrote:
> > Skipper:
> >
> > First, thanks for your help! :-)
> >
> > On Wed, Jun 16, 2010 at 7:19 AM, Skipper Seabold <jsseabold@gmail.com>
> > wrote:
> >>
> >> On Tue, Jun 15, 2010 at 8:38 PM, David Goldsmith
> >> <d.l.goldsmith@gmail.com> wrote:
> >> > Hi!  IMHO, the descriptions of the *args & **kwds parameters of the
> >> > Subject-referenced method are not very clear, so let me see if I
> >> > understand
> >> > correctly:
> >> >
> >>
> >> I agree and was having a look at this last week.  Here's my take.  I
> >> would err on the side of verbose in these docs, as the stats docs seem
> >> to be a general source of confusion from comments I've received off
> >> list, though obviously Josef, Travis, and others would know the
> >> details better than I.
> >>
> >> > *args : float(s), optional
> >> >     If the distribution in question depends on n parameters,
> _excluding
> >> > location and scale_, then *args may contain 0 to n floats, which are
> >> > starting estimates for the corresponding parameters.  No default
> >> > value(s).
> >> >
> >>
> >> I would add a note that n can be found in the numargs attribute of the
> >> distribution.
> >>
> >> > **kwds _may_ contain the following:
> >> >
> >> > loc : float, optional
> >> >     Starting estimate for the location parameter, no default.
> >> >
> >> > scale : float, optional
> >> >     Starting estimate for the scale parameter, no default.
> >>
> >> If the extra args *and* loc *and* scale are not specified, then the
> >> default starting estimates for loc, scale, and args are taken from the
> >> distribution's _fitstart(data) method.  I think it would make more
> >> sense to take the defaults for ones that are not provided by the user
> >> only, but this is not how the code reads at the moment as far as I can
> >> tell.
> >
> > So I can ignore this comment, correct?  If not, we once again have the
> > issue: document desired/intended behavior, if that differs from extant
> > behavior...
>
> Yeah, you can ignore this comment.  Anything the user gives is not thrown
> away.
>
> >>
> >> > floc : bool, optional
> >> >     Hold the location parameter constant; default: False.
> >> >
> >>
> >> floc : float, optional
> >>    Hold the location parameter constant at the given value.  Default:
> >> Fit this parameter using the data.
> >
> > So does this override a value provided by loc?  Is one supposed to not
> > specify both loc and floc?  What happens if one does? Is an exception
> > raised?
>
> Yeah.  If floc, or whatever is provided, then it is always passed to
> nnlf (negative log likelihood that we are minimizing).  So it's not
> technically wrong to pass a starting loc, but it doesn't make any
> difference for the fitting because it never gets used.
>

Ah, that's important to note as well.  Thanks!

DG


>
> >>
> >> > fscale : bool, optional
> >> >     Hold the scale parameter constant; default: False
> >> >
> >>
> >> See above.
> >
> > Ditto.
> >>
> >> > fi : bool, optional
> >> >     Hold the i-th scale parameter constant; there may be up to
> len(args)
> >> > of
> >> > these; default: False
> >> >
> >>
> >> I would keep it as something like
> >>
> >> f1...fn : float, optional
> >>   Hold shape parameter fi constant at the given value, where i may be
> >> 1 to numargs of the distribution.
> >
> > Ditto.
> >
> > DG
> >
> >
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> >
> >
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