Re: Error in "fit" documentation?

[Bastian M. <bma...@we...>]

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.

Actually, the code says

     columns = df_open(file_name, 7, NULL);    /* up to 7 using specs 
allowed */

df_open() is supposed to "return number of using specs", so columns == 0 
if we do not have using specs. The number of indep. variables is 
determined in the following line:

     num_indep = (columns < 3) ? 1 : columns - 2;

Which means num_indep == 1 without using specs.

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.

   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