Hello everyone,
TH1 histograms keep track of the total sum of weights, of the total sum of squares of weights, of the total sum of weight * X, and of the total sum of weight * X * X. These can be accessed via TH1::GetStats.
Is the total sum of weight * weight * X * X also computed? It is useful when one wants to evaluate the variance of weight*X.
Hi,
The histogram does not store the sum of weight * weight * X * X. But, why would you need to for ? One is interested in the weighted variance of X not the variance of weight * X.
If this is what you need fill an histogram with (weight * x) as new variable X
I understand this may be a niche application, but when computing a weighted average it can be useful to evaluate the numerator, sum w_i x_i, and the denominator, sum w_i, separately, and to combine them at a later stage. To keep track of uncertainties, this requires the variance of weight * x to be evaluated.
If this is what you need fill an histogram with (weight * x) as new variable X
Indeed, this seems to be the best solution given what ROOT currently does.