Hello Aihong,
Replace your statement:
TGraph *gr=new TGraph();
by
TGraph *gr=new TGraph(6);
Also note that the point numbering should start at 0, not 1
In my development version, I have protected TGraph::Fit in case the
graph
object was created via the default constructor.
Always specify the true number of effective points in the TGraph
constructor.
This is much more efficient. It avoids two arrays relocation for every
SetPoint.
Rene Brun
aihong@cnr2.kent.edu wrote:
>
> Hi,
>
> I got an error when using TGraph::Fit().the error message is the
> following:
>
> -------------------------------
>
> signal SEGV (no mapping at the fault address) in TGraph::Fit at line 676
> in file "G_Graph.cxx"
> 676 if (!Foption.Plus) fFunctions->Delete();
> (dbx) print fFunctions
> fFunctions = (nil)
>
> ----------------------------------
>
> It seems that fFunctions points to nothing.
> To reproduce the error, try to run the following macro:
>
> fittest (){
>
> TF1 *myfit = new TF1("myfit","[0]*sin(x) + [1]*exp(-[2]*x)", 0, 2);
>
> myfit->SetParName(0,"c0");
> myfit->SetParName(1,"c1");
> myfit->SetParName(2,"slope");
> myfit->SetParameter(0, 1);
> myfit->SetParameter(1, 0.05);
> myfit->SetParameter(2, 0.2);
>
> TGraph *gr=new TGraph;
> gr->SetPoint(1,0.4,0.45);
> gr->SetPoint(2,0.8,0.74);
> gr->SetPoint(3,1.2,0.97);
> gr->SetPoint(4,1.6,1.035);
> gr->SetPoint(5,1.4,1.02);
>
> gr->Fit("myfit","R");
> }
>
> Is there any solution for this ?
>
> I will appreciate any help. Thanks.
> Best Regards.
>
> Aihong
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