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## Re: [Help-gsl] Non-linear Multi-parameter Least-Squares Example

**From**: |
Gordan Bobic |

**Subject**: |
Re: [Help-gsl] Non-linear Multi-parameter Least-Squares Example |

**Date**: |
Fri, 20 Jul 2007 11:46:11 +0100 (BST) |

On Fri, 20 Jul 2007, John Gehman wrote:
[usefulness of sigma]
>* For the case where all data has the same error, as yours appears to, *
>* then all data is weighted equally. HOWEVER, this value does scale the *
>* residual and the sensitivity of the gradients, and I believe *
>* therefore does influence convergence. It may not make that big a *
>* difference in the regime where you are working, but I have noticed *
>* before with some of my applications that it was important to be *
>* realistic about the error.*
OK, I thoughts so. Effectively, it allows the fitter to get it slightly
wrong before cranking up the error.
Is there a way to supply a custom error function (e.g. via a callback) to
the fitter in GSL?
>* I'm not sure whether a gsl_vector_scale after the fact *
>* would be more efficient that explicit divisions during the loop?*
I'm not sure, but I think that would produce a different result...
Gordan

**Fwd: [Help-gsl] Non-linear Multi-parameter Least-Squares Example**, *John Gehman*, `2007/07/19`
**Re: [Help-gsl] Non-linear Multi-parameter Least-Squares Example**, *Gordan Bobic*, `2007/07/19`
**Re: [Help-gsl] Non-linear Multi-parameter Least-Squares Example**, *John Gehman*, `2007/07/19`
**Re: [Help-gsl] Non-linear Multi-parameter Least-Squares Example**, *Gordan Bobic*, `2007/07/20`
**Re: [Help-gsl] Non-linear Multi-parameter Least-Squares Example**, *John Gehman*, `2007/07/20`
**Re: [Help-gsl] Non-linear Multi-parameter Least-Squares Example**,
*Gordan Bobic* **<=**
**[Help-gsl] gsl_matrix_set()**, *Gordan Bobic*, `2007/07/20`
**Re: [Help-gsl] gsl_matrix_set()**, *Jordi GutiĆ©rrez Hermoso*, `2007/07/20`
**Re: [Help-gsl] gsl_matrix_set()**, *Gordan Bobic*, `2007/07/20`
**Re: [Help-gsl] gsl_matrix_set()**, *Martin Jansche*, `2007/07/22`
**Re: [Help-gsl] gsl_matrix_set()**, *Jordi GutiĆ©rrez Hermoso*, `2007/07/20`