Re: Error bars

From: Rene Brun <Rene.Brun_at_cern.ch>
Date: Mon, 29 Jan 2007 08:29:14 +0100

Monika,

If you create a TGraphErrors you don't need to create individual TMarkers. Simply do:

 Float_t x1[] = {Some values..........}
 Float_t y1[] = {Some values..........};
 Float_t ex[] = {0,0,0,0,0,0,0};
 Float_t ey[] = {0,0,0,0,0,0,0};

 gr1 = new TGraphErrors(n,x1,y1,ex,ey);

 gr1->SetMarkerColor(kBlue);
 gr1->SetMarkerSize(1.2);
 gr1->Draw("ap");

Rene Brun

Monika Sharma wrote:
>
> Hi Rene,
>
> I tried it this way :
>
> =======================================
> Float_t x1[] = {Some values..........}
> Float_t y1[] = {Some values..........};
> Float_t ex[] = {0,0,0,0,0,0,0};
> Float_t ey[] = {0,0,0,0,0,0,0};
> gr1 = new TGraphErrors(n,x1,y1,ex,ey);
> Double_t *nx = gr1->GetX();
> Double_t *ny = gr1->GetY();
> Double_t *ney = gr1->GetEY();
> Double_t *nex = gr1->GetEX();
>
> for(Int_t i=0; i<8; i++)
> {
> TMarker *m = new TMarker(nx[i],ny[i],nex[i],ney[i],22);
> m->SetMarkerColor(kBlue);
> m->SetMarkerSize(1.2);
> m->Draw();
> }
> ===========================================
>
> But looks like I can only pass (gr1->GetX(), gr1->GetY(), MarkerStyle)
> and not the errors. Is there any way that I draw errors on these markers?
> Also, I didn't fine any function in TMarker class which can return me
> errors in gr1.
>
> Thanks
> Monika
>
> Rene Brun wrote:
>
>> Monika Sharma wrote:
>>
>>>
>>> Hi Rooters,
>>>
>>> I have been using the demo example given in Chapter 4 (Graphs), page
>>> 53,
>>> in User's guide. This program draws markers with different colours
>>> taking
>>> input from graph, i.e.,
>>>
>>> Double_t *nx = gr3->GetX();
>>> Double_t *ny = gr3->GetY();
>>>
>>> I wanted to ask is there any way with which it can take errors
>>> too........
>>> Something like :
>>>
>>> Double_t *nex = gr4->GetEX();
>>> where gr4 is TGraphErrors and EX is the error on x
>>> Is it possible?
>>
>> YES. In the example replace TGraph by TGraphErrors and define your
>> errors in x and/or y
>>
>> Rene Brun
>>
>>>
>>> Thanks
>>> Monika
>>
Received on Mon Jan 29 2007 - 08:29:25 CET