OLSZEWSKI@vsk02.ifj.edu.pl wrote: > > Hi, > > There is a difference in behaviour between PAW and ROOT in function > normalization after it was fit to a histogram. In PAW I get the same > sum of weigths for a function and a histogram. In ROOT function is > visualized by default in a 100 bin histogram, independend of the number > of histogram bins. Then the two sums of weights differ. > If the above is true it should be either changed or a warning somewhere > should be placed. By default, Root always draws the fitted function computed at 100 equidistant points. This is better than PAW when drawing histograms with only a few channels. The chunk of code below is an example illustrating how to get a fitted function associated to an histogram and how to return the function integral normalized to the number of bins in in the histogram: Root > h->Fit("gaus"); Root > TF1 *g = h->GetFunction("gaus"); Root > TH1F *htemp = g->GetHistogram(); Root > Double_t integral = htemp->GetSum()*h->GetNbinsX()/100. Note that this example is valid only for a fixed bin size histogram. We should may be provide a service function in TH1 returning the integral (normalized or not) of a function with a given name. (More than one function can be fitted to an histogram). Rene Brun
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