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Re: doubt in chisq value [message #73213]

Mon, 01 November 2010 07:48

wlandsman
Messages: 743
Registered: June 2000

Senior Member

On Nov 1, 2:43 am, sid <gunvicsi...@gmail.com> wrote:
> Hi,
> I am fitting my data with svdfit (2 degree polynomial), now I need
> to know how exactly the chisq value is calculated in this routine,
> because I need to know the goodness of fit. For my data which I am
> fitting I am getting chisq values which varies from 6.3534419e-07 to
> 8.0278877e-09 for different datasets. But please help how the routine
> is performing the chisq calculation and how can I find the goodness of
> fit from it.
> thanking you
> sid

You are almost certainly supplying unrealistic error bars (sigma
values).
Chisq can be calculated from the single line (e.g. see curvefit.pro)

chisq = total(Weights*(y-yfit)^2)/nfree

where weights = 1/sigma^2 , and nfree is the number of data points
minus the number of free parameters.

--Wayne

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		Re: doubt in chisq value By: wlandsman on Mon, 01 November 2010 07:48
		Re: doubt in chisq value By: sid on Tue, 02 November 2010 00:29

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