Re : [ROOT] TProfile2D and projections

From: Rene Brun (Rene.Brun@cern.ch)
Date: Sat Jul 12 2003 - 15:16:21 MEST


Hi Aaron,

Sorry for the long delay to answer this mail. I did not see your original mail.


If instead of:
 aP2D->ProjectionX("prox",20,20)->Draw();
you do:
 aP2D->ProjectionX("prox",20,20)->Draw("e");
you will see the error bars.

If instead of;
 aP2D->ProjectionX("prox",20,21)->Draw();
you do:
 aP2D->ProFileX("prox",20,21)->Draw();

you will obtain what you required for your second option.

Rene Brun



> Rooters,
> 
>       Lately I've been using the very useful TProfile2D type of histogram,
> and would find it very convenient to be able to use Profiles of these
> histograms.
> However, projections of TProfile2D's do not behave in the expected way. (I'm
> using 3.05.02 on Linux)
> 
>         Using the example below, a Projection of just one bin has the values
> from
> that bin, but no errors.  It would be nice to have the errors displayed.
> 
>         Next, when projecting over more than one bin, one gets the sum of
> the
> bins included.  Given that it is a Profile histogram, it would make more
> sense
> to get the average, with the errors calculated in the same way as the
> original
> Profile histogram.
> 
>        regards,
>                Aaron Roodman
> 
> TProfile2D* aP2D = new TProfile2D("aP2D","test
> Profile",40,-4.,4.,40,-4.,4.);
> for
> (Int_ti=0;i<10000;i++){aP2D->Fill(gRandom->Gaus(),gRandom->Gaus(),gRandom->
> Gaus());}
> aP2D->ProjectionX("prox",20,20)->Draw();
> aP2D->ProjectionX("prox",20,21)->Draw();
>



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