TH1F *h2=new TH1F("h2","h2",4,-0.5,3.5);
Float_t err = 0.0001;
h2.Fill(0,4); h2.SetBinError(1,err);
h2.Fill(1,3); h2.SetBinError(2,err);
h2.Fill(2,2); h2.SetBinError(3,err);
h2.Fill(3,1); h2.SetBinError(4,err);
h2.Fit("pol1");
Concerning your attempt with TGraph, note that TGraph accepts
floats not ints. You should have:
Float_t x[4]={0,1,2,3};
Float_t y[4]={4,3,2,1};
TGraph *g1=new TGraph(4,x,y);
Rene Brun
Tadeusz Pytlos wrote:
>
> Dear Rooters,
> My problem seems to be easy, but I lost a lot of time with it.
> Let's assume I have got a histogram of integers
>
> -
> - -
> - - -
> - - - -
> 0 1 2 3
>
> According to simple matematics fitting by y=p0+p1*x should give
> p0=4 and p1=-1, errors=0.
> How could I fix a range or sth other
> to receive the best fiting results?
> I'm using ROOT 2.00/11 RedHat 5.0.
> Best wishes,
> Tadeusz
>
> root [0] TH1S *h1=new TH1S("h1","h1",4,0,4)
> root [1] h1.Fill(0,4)
> root [2] h1.Fill(1,3)
> root [3] h1.Fill(2,2)
> root [4] h1.Fill(3,1)
> root [5] h1.Fit("pol1")
> **********
> ** 1 **SET ERR 1
> **********
> FCN=0 FROM MIGRAD STATUS=CONVERGED 22 CALLS 23 TOTAL
> EDM=8.30088e-33 STRATEGY= 1 ERROR MATRIX
> ACCURATE
> EXT PARAMETER STEP FIRST
> NO. NAME VALUE ERROR SIZE DERIVATIVE
> 1 p0 4.50000e+00 1.83007e+00 -0.00000e+00 0.00000e+00
> 2 p1 -1.00000e+00 6.56532e-01 0.00000e+00 -2.77547e-16
> Warning in <MakeDefCanvas>: creating a default canvas with name c1
>
> root [6] TH1F *h2=new TH1F("h2","h2",4,-0.5,3.5)
> root [7] h2.Fill(0,4)
> root [8] h2.Fill(1,3)
> root [9] h2.Fill(2,2)
> root [10] h2.Fill(3,1)
> root [11] h2.Fit("pol1")
> FCN=0 FROM MIGRAD STATUS=CONVERGED 20 CALLS 21 TOTAL
> EDM=1.00357e-30 STRATEGY= 1 ERROR MATRIX
> ACCURATE
> EXT PARAMETER STEP FIRST
> NO. NAME VALUE ERROR SIZE DERIVATIVE
> 1 p0 4.00000e+00 1.53128e+00 1.20000e-03 -9.25194e-16
> 2 p1 -1.00000e+00 6.56532e-01 3.00000e-04 0.00000e+00
>
> root [12] Int_t x[4]={0,1,2,3}
> root [13] Int_t y[4]={4,3,2,1}
> root [14] TGraph *g1=new TGraph(4,x,y)
> Error: Can't call TGraph::TGraph() in current scope FILE:/tmp/19719caa
> LINE:1
>
> --
> Tadeusz Pytlos
> mailto:pytlos@fizwe5.fic.uni.lodz.pl
> Lodz, Poland