Re: Polynomial regression - Warning

[Prof J C Nash <nashjc ncf ca>]

The type of dialog Adrian suggests would be a very sensible feature. 
Sometimes one really does need to do the polynomial regression, even if 
to show the issues, so it is not right to completely bar an approach. 
However, when we have an interested person, it's a good opportunity to 
point them towards potentially better methods. There was some discussion 
of such dialogs in the 80s for statistical software, and there's some of 
these ideas in some of the packages. Certainly I'm interested in helping 
out on this sort of thing, and have been gradually clawing away at other 
stuff I have to do so I can return to the test spreadsheets, which are 
one way to bring the issues to light.

JN


Adrian Custer wrote:
> Lovely repartee, just the sophisticated answer that gnumeric brings to
> the spreadsheet world.
>
> Any chance you can craft this into a good popup dialog? e.g.
>
>         You are trying to use SOME_METHOD which exists in gnumeric only
>         to allow compatibility with other older spreadsheet programs.
>         The computations involved in that method are known to be
>         exceedingly problematic. However, you might be able to solve
>         your problem using SOME_OTHER_METHOD. Would you like to use that
>         instead?
>
> Of course, this is all over my head. I'm merely hoping to leverage your
> 40 years of knowledge into a helpful dialog.
>
> --adrian
>
>
> On Tue, 2007-10-09 at 14:46 -0400, Prof J C Nash wrote:
>   
> > Polynomial regression was where I came into numerical analysis at the 
> > beginning of my academic career 40 years ago. It is a dangerously 
> > ill-conditioned problem, meaning that the regression parameters are 
> > untrustworthy, though the "fit", i.e., the model, may be useful if the 
> > calculations are done properly. There are ways of doing it that are 
> > "less dangerous" using orthogonal polynomials.
> >
> > Just a warning that it should not be a high priority to add. Let the 
> > Excel users drive off the cliff. If it is added for Excel compatibility, 
> > then I'd still recommend a "Gnumeric does Vista" and pop up warnings 
> > asking if the dangerous move should be allowed. Come to think of it, one 
> > could borrow exactly the Vista popups so folk would blame Bill.
> >
> > Seriously, think if you really need polynomial regression or can use a 
> > less troublesome approach.
> >
> > JN
> >
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