[ROOT] What does negative zero mean?

From: Dongwook Jang (dwjang@fnal.gov)
Date: Thu Apr 01 2004 - 21:23:57 MEST


Hi,

I had problem to divide histograms.
During simplified my problem, I found something strange.

void test()
{

   TH1F* dH = new TH1F("dH","dH",10,0,10);
   TH1F* nH = new TH1F("nH","nH",10,0,10);
   TH1F* rH = new TH1F("rH","rH",10,0,10);

   for(Int_t i=2; i<8; i++){
     dH->SetBinContent(i,i);
     nH->SetBinContent(i,i);
   }

   rH->Sumw2();
   rH->Divide(nH,dH,1,1,"B");
   rH->SetMarkerStyle(20);
   rH->SetMarkerColor(2);
   rH->Draw("e");

   for(Int_t i=1; i<=10; i++){
     cout << i << "\t : " << rH->GetBinContent(i)
	 << ", " << rH->GetBinError(i) << endl;
   }

}

I expected exact 1 efficiency plot, but I got the following:

<output> :

No points are ploted at all.

root [0] .x test.C
<TCanvas::MakeDefCanvas>: created default TCanvas with name c1
1        : 0, 0
2        : 1, -0
3        : 1, -0
4        : 1, -0
5        : 1, -0
6        : 1, -0
7        : 1, -0
8        : 0, 0
9        : 0, 0
10       : 0, 0
root [1]


-- 

Best regards,
Dongwook Jang.
phone :	630-840-2118 (office B0 170-I) 630-840-6315 (FAX)



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