filling TGraphAsymmErrors

From: <nguler_at_jlab.org>
Date: Mon, 2 Nov 2009 21:41:40 -0500

Hello,
I use Root version 5.22/00
To plot systematic errors, I was generally using TGraphErrors with P3 drawing option. This fills the systematic error (plus-minus) region symmetrically around an offset I determine. Recently, I was asked to plot systematic errors only as an absolute value (not symmetric around an offset but only from offset to sysErr value). I tried TGraphAsymmErrors for that purpose, assigning 0 error values for the negative side errors. If I could not express myself, please take a look at a simple code I wrote to replicate the problem I will describe.

TGraphAsymmErrors sometime gives erratic fill behavior, it fill places it should not. After a long trial and error, I believe I pinpointed the source of the problem: If the frame's maximum x range is smaller than the array's x range I put into the TGraphAsymmErrors, then I see this behavior. But, I would like my frame's x range to be a variable, to be able to zoom in certain parts, so the frames minimum and maximum x ranges can be smaller or larger than the array's x ranges. But TGraphAsymmErrors does not like that. Maybe I am missing an important piece of information on how to use TGraphAsymmErrors.

I am printing the sample code below to replicate the problem. I will appreciate your help if there is a way around this. Or, you can tell me if there is a better way to plot various systematic error (from offset to sysErrvalue), for various offsets. Thank you very much.

• Nevzat Guler

{

    double x[15] = {

      0.1,0.2,0.3,0.4,0.5,
      0.6,0.7,0.8,0.9,1.0
      1.1,1.2,1.3,1.4,1.5};

    double xErr[15] = {0.0};

    double y[15] = {

      0.1,0.2,0.3,0.4,0.3
      0.1,0.2,0.3,0.4,0.3
      0.1,0.2,0.3,0.4,0.3};
    double ySys[15] = {
      0.00,0.05,0.06,0.07,0.06,
      0.07,0.05,0.00,0.00,0.07,
      0.08,0.00,0.00,0.00,0.00};

      double yErr[15] = {0.0};
      double yOff1[15] = {0.0};
      double yOff2[15] = {0.0};
      for(int i=0;i<15;i++){
          yErr[i] = 0.1;
          yOff1[i] = -0.8;
          yOff2[i] = -0.5;
      }

    TCanvas *c1 = new TCanvas("c1","c1",0,0,400,400);     c1->Modified();
    c1->Update();

    TH1 *frame1 = c1->DrawFrame(0,-1,1,1);
//// above gives erratic fill behavior for sys error
//// because maximum x range is smaller than the value of highest x

    //TH1 *frame1 = c1->DrawFrame(0,-1,2,1);
//// this one works fine apparently

    frame1->GetXaxis()->SetTitle("x");
    frame1->GetXaxis()->CenterTitle();
    frame1->GetYaxis()->SetTitle("y");
    frame1->GetYaxis()->CenterTitle();

    TGraphErrors *TG1 = new TGraphErrors(15,x,y,xErr,yErr);

    TG1->SetMarkerColor(kRed);
    TG1->SetLineColor(kRed);
    TG1->SetMarkerStyle(20);
    TG1->Draw("P");

//// this draws sys symmetrically around the offset
    TGraphErrors *TG2 = new TGraphErrors(15,x,yOff1,xErr,ySys);

    TG2->SetMarkerColor(kBlue);
    TG2->SetFillColor(kBlue);
    TG2->Draw("P3");

//// this draws sys one sided from offset to up
//// this is what we want

    TGraphAsymmErrors *TG3 = new TGraphAsymmErrors(15,x,yOff2,0,xErr,0,ySys);

    TG3->SetMarkerColor(kRed);
    TG3->SetFillColor(kRed);
    TG3->Draw("P3");

} Received on Tue Nov 03 2009 - 03:41:46 CET