How to perform least square and modified least square fit using ROOT?

[realTay_John]

Hi experts,
Here is the definition of Least square and modified least square.
How to perform them respectively, or if there is some options could be used to realise them?
Thank you.

[Wile_E_Coyote]

Search for “Neyman”, “Pearson”, and “Baker” (or “Cousins”) chi-square in the TH1 Class Reference (and/or elsewhere).

See also:

Chi-square definition in ROOT

Hi All, My co-worker and I, using different tools, were trying to fit some histograms. Surprisingly, we found the chi2 of our results were different by 1.5 to 2 times. Here is a toy histogram for example: Bin centres: [0.025, 0.075, 0.125, 0.175, 0.225, 0.275, 0.325, 0.375, 0.425, 0.475, 0.525, 0.575, 0.625, 0.675, 0.725, 0.775, 0.825, 0.875, 0.925, 0.975] Bin edges: [0., 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.] Bin heights: […