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Doubt in polynomial fitting - emergency [message #73347]

Tue, 02 November 2010 01:39

sid
Messages: 50
Registered: January 1995

Member

Hi,
I am fitting my spectral data with 2 degree polynomial with the
routine svdfit. I need to find the minmum value after fitting the data
points.
For example my code is like this,
;c is x axis with wavelength(it is an absorption line)
;d is y axis with normalised intensity
ypoly=svdfit(c,d,3,yfit=y1,chisq=chi,sigma=sig)
x=min(y1)
x1=-(ypoly(1))/(2*ypoly(2))
if suppose u,v is the position of x, x1 respectively then
c(u) should be equal to c(v)
and
d(u) should be equal to d(v)
but im getting
c(u)=3933.3090 in angstroms
c(v)=3933.3072 in angstroms
d(u)=0.071168385
d(v)=0.072779992
Please suggest me why it is not the same, which value should I believe
and how?
thanking you
sid

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