Hi guys,

I have two correlated histograms AAAA, BBBB.

likes:

```
TH1D* AAAA = (TH1D*)file1->Get("");
TH1D* BBBB = (TH1D*)file1->Get("");
```

I want to calculated the statistical uncertainty for the sum of AAAA->Add(BBBB).

By default, I used the sumw2(). I know sumw2 is only correct to two independent histograms.

So, how will I do? It is better if give a corresponding example.

Thanks a lot.