Re: Error in "fit" documentation?

[sfeam (E. Merritt) <eam...@gm...>]

On Thursday, 13 June 2013, Bastian Märkisch wrote:
> Am 14.06.2013 02:07, schrieb Ethan A Merritt:
> > Current documentation for "fit" says
> >
> >    Note that if you don't pecify a `using` option at all, no z standard
> >    deviations are read from the datafile even if it does have a third
> >    column, so you'll always get unit weights.
> >
> > But from looking at the code I think this is not true.  If there is
> > no using spec then the number of independent variables is always two
> > less than the number of columns in the input file, and the final
> > input column is indeed interpreted as a standard deviation on z.
> >
> I think the documentation is correct, albeit somewhat unclear. 
> Previously fit used to support only a maximum of two independent 
> variables and I think this statement stems from that era as it refers to 
> a "third" column.

> And later, the "error" is saved by the following line:
> 
>      /* only use error from data file if _explicitly_ asked for by
>       * a using spec
>       */
>      err_data[num_data++] = (columns > 2) ? v[i] : 1;
> 
> Again, we obtain unit weight without using specs.

OK, I see now.  The value "columns = 0" is carried all the way through to
this line if there is no using spec.    This is the first time I've looked at
the code in fit.c, so I'm still learning my way around it.

	Ethan

>    Bastian
> 
> > The comment in the fit.c source code is also wrong, as it claims
> > that the standard deviation is used only if there is an explicit
> > using spec.
> >
> > Have I misread this?
> >
> > 	Ethan
> 
> 
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