--------------------------------------------------
After 1 iterations the fit converged.
final sum of squares of residuals : 9.65289
rel. change during last iteration : -1.84023e-016
degrees of freedom (FIT_NDF) : 2
rms of residuals (FIT_STDFIT) = sqrt(WSSR/ndf) : 2.19692
variance of residuals (reduced chisquare) = WSSR/ndf : 4.82645
Final set of parameters Asymptotic Standard Error
======================= ==========================
a = 1.71413 +/- 0.3239 (18.9%)
b = -1.16815 +/- 1.957 (167.5%)
correlation matrix of the fit parameters:
a b
a 1.000
b -0.828 1.000
--------------------------------------------------
The fit seems to work, but if I change the input data, the correlation matrix does not change!? I always get -0.828.
Or do I misunderstand something and this is correct?
Thank you for answers,
Sammylight
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
but it seems any input data leads to the same correlation matrix. Or is this matrix only related to the fit - function? I expected something like correlation coefficients. !?
(gnuplot version 4.2 patchlevel 0)
Kind regards,
Sammy :)
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
You're getting correlation coefficients. A change as small as that just doesn't have a lot of influence on C_ab. You have to move it more to see an effect on the correlation.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
If I fit the data
1 2.5
3 2.1
6 8
10 17.01
using
f(x) = a*x+b
I get
--------------------------------------------------
After 1 iterations the fit converged.
final sum of squares of residuals : 9.65289
rel. change during last iteration : -1.84023e-016
degrees of freedom (FIT_NDF) : 2
rms of residuals (FIT_STDFIT) = sqrt(WSSR/ndf) : 2.19692
variance of residuals (reduced chisquare) = WSSR/ndf : 4.82645
Final set of parameters Asymptotic Standard Error
======================= ==========================
a = 1.71413 +/- 0.3239 (18.9%)
b = -1.16815 +/- 1.957 (167.5%)
correlation matrix of the fit parameters:
a b
a 1.000
b -0.828 1.000
--------------------------------------------------
The fit seems to work, but if I change the input data, the correlation matrix does not change!? I always get -0.828.
Or do I misunderstand something and this is correct?
Thank you for answers,
Sammylight
> but if I change the input data, the correlation matrix does not change!?
If you don't say *how* you changed that input, it's quite impossible to tell what the correlation matrix should be.
I changed for example to
from input data
1 2.5
to
1 2.0
but it seems any input data leads to the same correlation matrix. Or is this matrix only related to the fit - function? I expected something like correlation coefficients. !?
(gnuplot version 4.2 patchlevel 0)
Kind regards,
Sammy :)
You're getting correlation coefficients. A change as small as that just doesn't have a lot of influence on C_ab. You have to move it more to see an effect on the correlation.