True I had a typo but somehow it was fitting. But as I changed it the error band blows up and still shrinks in the middle.
I have attached the roofit logs containing the fit parameters, errors etc(v0 is for typo and v1 after correcting typo to minuit). There seems to be roofit errors(negative diagonal elements in error matrix) in both the logs but it is hard for me to figure what could be resulting in that.
Initialization of the coefficients seems to affect it. So I changed all the initial values to 1 keeping bounds the same. The error matrix issue got resolved and error band doesn’t blow up but still the error band shrinks in middle. Also attached the roofit log (v2) and plot for the same.
And it says.
MIGRAD MINIMIZATION HAS CONVERGED.
MIGRAD WILL VERIFY CONVERGENCE AND ERROR MATRIX.
COVARIANCE MATRIX CALCULATED SUCCESSFULLY
Roofit Logs:
roofit_log_v0.txt (238.6 KB)
roofit_log_v1.txt (295.8 KB)
roofit_log_v2.txt (227.2 KB)
Fit plots:
