Hi!
Thanks a lot for your help.
I don't know why but the first option is not giving me the correct
histogram, in fact histo h1 shows no entry at all with some strange
looking plot. But the 2nd option (shorter one) is working fine.
Actually I have one histogram in which I have to fit a given small range
by linear fit (pol1). Then using its parameters p0 and p1, I have to
extrapolate that linear fit to larger range (but still not the whole
range).
Next I want to take the difference between the histo content up to the
larger ranger and the combined linear fit.
For that I am doing the following:
//1d projection of 2d histgram with 50 bins
> TH1D *h = (TH1D*) h_ave->ProjectionY("", 29, 29);
//fitting in small range
> TF1 *pol1 = new TF1("pol1","pol1",0,h->GetBinContent(20));
> h->Fit("pol1","R");
//getting fit parameters p0 & p1
>Double_t po1 = pol1->GetParameter(0);
>Double_t po2 = pol1->GetParameter(1);
//define a linear function myfun with two parameters, and setting the
two values previously obtained from pol1
>TF1 *myfun = new TF1("myfun", "[0]+[1]*x",h->GetBinContent(21),
h->GetBinContent(bin));
> myfun->SetParameters(po1,po2);
> h->Fit("myfun",R+);
// Then combining two fits into single fit
>TF1 *total = new TF1("total","pol1+myfun",0,h->GetBinContent(bin));
>h->Fit("total","R+");
//and then the subtraction for which I am using your second option.
>TH1F *h1 = (TH1F*)h->Clone("h1");
> h1->Add(h->GetFunction("total"),-1);
// But then when I subtract using clone, I get the subtraction over the
whole range which I want to be limited to some h->GetBinContent(bin). I
also don't know if this is the right methodology or not. I did not get
much from the multifit tutorial also.
Please help.
Thanks a lot,
kirti.
----- Original Message -----
From: Rene Brun <Rene.Brun@cern.ch>
Date: Wednesday, November 19, 2003 2:36 am
Subject: Re: [ROOT] How to take the diff. b/w histo contents and fit
> Hi Kirti,
>
> After the fit, ou can do something like
>
> TF1 *func = h->GetFunction("pol1");
> for (int bin=1, bin<=nbins;bin++) {
> double x = h->GetXaxis()->GetBinCenter(bin);
> double fval = func->Eval(x);
> h1->SetBinContent(bin,h->GetBinContent(bin)-fval);
> }
>
> or even simpler
>
> TH1F *h1 = (TH1F*)h->Clone("h1");
> h1->Add(h->GetFunction("pol1"),-1);
>
> Rene Brun
>
>
> kirti@fnal.gov wrote:
> >
> > Hi again!
> > I have one more query:
> >
> > I am plotting one dim. histogram and then fit it with linear(po1)
> fit in
> > some specified range.
> >
> > >TH1D *h = (TH1D*) h_ave->ProjectionY("", 29, 29);
> >
> > //where h_ave is 2D histogram. There are 50 bins and the maximum
> value> in this plot goes up to 20000.
> >
> > >TF1 *pol1 = new TF1("pol1","pol1",0,2000);
> > h->Fit("pol1","R");
> >
> > I would now like to take the difference between the two i.e., Fit
> and> original Histogram, and plot it.
> >
> > For histogram I can find the Bin Content by using:
> > >for(bin=0; bin<50;bin++)
> > h1->SetBinContent(1+bin,h->GetBinContent(1+bin));
> >
> > But I do not understand how to find the bin content for Fit and then
> > take the differnce.
> > Please suggest.
> > Kirti
> >
> >
> >
>
>
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