Re: Zooming problem with TGraph

From: Rene Brun <Rene.Brun_at_cern.ch>
Date: Sat, 29 Apr 2006 09:16:57 +0200 (MEST)

The zoom precision corresponds to the number of bins along x or y. In case of log scales and a big range (in your case 1e-2 to 1e6) the current algorithm may fail if the number of bins is too small. I habve modified your program to be able to zoom more deeply in your graph. see below.

Rene brun

void leggi()
{

   TCanvas *c1= new TCanvas("c1","c1",200,10,700,500);

   c1->SetLogy(kTRUE);
   c1->SetLogx(kTRUE);
   c1->SetGrid(kTRUE);

   int nlines=0,n=0;
   FILE *file;
   file=fopen("xs.dat","r");
   if(file==NULL)

     {
        cout << "Errore apertura file!" << endl;
     }

   char riga[10000];
   float energy_,xs_,xserr_;
   float energy[10000],xs[10000],xserr[10000];    while(fscanf(file,"\n%[^\n]",riga)>EOF)

     {
        sscanf(riga, "%f %f %f", &energy_,&xs_,&xserr_);
        energy[n]=energy_;
        xs[n]=xs_;
        xserr[n]=xserr_;
        nlines++;
        n++;
     }

   fclose(file);
   cout << nlines << endl;

   TGraphErrors *gr = new TGraphErrors(nlines,energy,xs,0,xserr);

   gr->SetMarkerStyle(21);
   gr->SetMarkerSize(0.5);
   gr->SetMarkerColor(4);

   TH1C *hpx = new TH1C("hpx","Sezione
d'urto^{245}Cm",1000000,0.01,5000000);

   hpx->SetStats(kFALSE);
   hpx->Draw();
   hpx->SetMinimum(0.01);
   hpx->SetMaximum(5000000);
   hpx->GetXaxis()->CenterTitle();
   hpx->GetXaxis()->SetTitle("E_{n} (eV)");
   hpx->GetYaxis()->CenterTitle();
   hpx->GetYaxis()->SetTitle("#sigma (barn)");

   gr->Draw("lp");
}

On Fri,
28 Apr 2006, Marco Calviani wrote:

> Hi rooters,
> i'm trying to create a graph (with bar errors) using TGraphErrors,
> reading the data from an ASCII file. It succesfully creates the graph
> but when i try to zoom or on the X or on the Y axis, the lowest limit
> remains blocked on the minimum. How is it possible?
>
> void leggi()
> {
> TCanvas *c1= new TCanvas("c1","c1",200,10,700,500);
> int nlines=0,n=0;
> FILE *file;
> file=fopen("xs.dat","r");
> if(file==NULL)
> {
> cout << "Errore apertura file!" << endl;
> }
>
> char riga[10000];
> float energy_,xs_,xserr_;
> float energy[10000],xs[10000],xserr[10000];
> while(fscanf(file,"\n%[^\n]",riga)>EOF)
> {
> sscanf(riga, "%f %f %f", &energy_,&xs_,&xserr_);
> energy[n]=energy_;
> xs[n]=xs_;
> xserr[n]=xserr_;
> nlines++;
> n++;
> }
> fclose(file);
> cout << nlines << endl;
>
> TH2F *hpx = new TH2F("hpx","Sezione d'urto
> ^{245}Cm",nlines,0.01,5000000,1000,0.01,10000.);
> hpx->SetStats(kFALSE);
> hpx->Draw();
> hpx->GetXaxis()->CenterTitle();
> hpx->GetXaxis()->SetTitle("E_{n} (eV)");
> hpx->GetYaxis()->CenterTitle();
> hpx->GetYaxis()->SetTitle("#sigma (barn)");
> TGraphErrors *gr = new TGraphErrors(nlines,energy,xs,0,xserr);
> gPad->SetLogy(kTRUE);
> gPad->SetLogx(kTRUE);
> gPad->Modified();
> gPad->Update();
> gr->SetMarkerStyle(21);
> gr->SetMarkerSize(0.5);
> gr->SetMarkerColor(4);
> gr->Draw("LP");
> c1->SetGrid(kTRUE);
> c1->Modified();
> c1->Update();
> }
>
> Many thanks in advance,
> MC
>
Received on Sat Apr 29 2006 - 09:17:01 MEST