Hi, Rooters.
Could you let me have some hints for using TMinuit with user chi2 construction.
My condition for fit is a 2-dim. polynomial fit, i.e. I need to minimize chi2 according to below
dx = a0 + a1*x + a2*y
dy = b0 + b1*x + b2*y
-
for 2 parameter fit, i.e,
dx = a0
dy = b0,
I could get same results what I expected, however it has very large error as
FCN=5.00325e-15 FROM MIGRAD STATUS=CONVERGED 23 CALLS 24 TOTAL
EDM=1.94118e-28 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 3.28514e-10 2.56326e-02 1.00000e-12 -2.83515e-13
2 p1 9.44186e-10 2.56326e-02 1.00000e-12 -7.14503e-13
I guess, it would be due to issue of order of data. (x and y is order of 10^-3 while error of x and y is order of 10^-6). If so, how can I have reasonale fit result?
- For 6 par or more high order polynomials, I could not get values as what I expected (from another more than two tools). Could you help me whether I constructed a wrong chi2, even though 2 par result looks fine?
I attach my data and running scripts.
Thanks in advance,
H.H
fit2pv1.C (2.5 KB)
fit6pv1.C (3.1 KB)
sample.txt (60.2 KB)