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Re: polyfit: add the ability to specify the polynomial template
From: |
CdeMills |
Subject: |
Re: polyfit: add the ability to specify the polynomial template |
Date: |
Sun, 5 Feb 2012 08:56:54 -0800 (PST) |
Jordi Gutiérrez Hermoso-2 wrote
>
>
> Okay, thanks. I didn't notice before that you wanted to patch on
> stable. The current plan is to be very conservative about patching
> stable, and only we only fix regressions and critical bugs on stable.
> I think this should be done on default instead.
>
> Or is there a reason I'm not seeing for why this is a regression or
> critical bug?
>
>
The actual implementation gives a false sense of security. Ask for some
model order, and you'll get back a coefficients set. The condition of the
design matrix is not tested. If you have a look in polyval.m, line 78:
dy = sqrt (1 + sumsq (A/s.R, 2)) * s.normr / sqrt (s.df);
the inverse of s.R is used, even if it does not make sense.
The modifications I made in polyfit:
- do not change the computation of s.R when n is a scalar
- already compute S.R inverse in s.C. If any value is NaN, then the design
matrix is not full rank, and the model order MUST be lowered.
So, I agree that in 99% of the cases the actual behaviour is not a
regression nor a bug. But in case of problems, you don't have specific
indicators about your model validity.
Regards
Pascal
--
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Sent from the Octave - Maintainers mailing list archive at Nabble.com.
- polyfit: add the ability to specify the polynomial template, CdeMills, 2012/02/04
- Re: polyfit: add the ability to specify the polynomial template, Ben Abbott, 2012/02/04
- Re: polyfit: add the ability to specify the polynomial template, Jordi Gutiérrez Hermoso, 2012/02/04
- Re: polyfit: add the ability to specify the polynomial template, CdeMills, 2012/02/05
- Re: polyfit: add the ability to specify the polynomial template, Jordi Gutiérrez Hermoso, 2012/02/05
- Re: polyfit: add the ability to specify the polynomial template,
CdeMills <=
- Re: polyfit: add the ability to specify the polynomial template, Jordi Gutiérrez Hermoso, 2012/02/07
- Re: polyfit: add the ability to specify the polynomial template, John W. Eaton, 2012/02/07
- Re: polyfit: add the ability to specify the polynomial template, CdeMills, 2012/02/07
- Re: polyfit: add the ability to specify the polynomial template, Jordi Gutiérrez Hermoso, 2012/02/07
- Re: polyfit: add the ability to specify the polynomial template, CdeMills, 2012/02/08
- Re: polyfit: add the ability to specify the polynomial template, Jordi Gutiérrez Hermoso, 2012/02/16