I have 1D histogram of experimental data. I have to fit with 5 MC 1D histograms. I fitted it but when I added all fractions of MC histogram, it did not give 1.0 but close to unity. Is there any way I can get unity it I add all fractions of MC histogram. I saw in TFractionFitter code, it is normalizing the factor. But, I am not getting it. I am new to TFractionFitter, it might be very stupid question. Thanks in advance.

The sum of the fitted fractions of TFractionFitter should be equal to 1. Maybe you are having a numerical error in the sum ?
If not, something else might not be correct. I would need in that case your code and input histograms

I want to minimize the fit by looping the fraction of hist_712 and finding the corresponding fractions of other MC histograms with minimum chisquare in each point in loop. I want how other fractions of simulated histograms change with change in fraction of hist_712. I added the all fraction values before and after the fit. I chose initial fractions first getting minimization without loop and adjust to make sum before fit equal to unity ( you can also check). But after the fit in loop, the sum of all fractions is not exactly unity. Thank you in advance.