TProfile::Scale() and bin errors

From: Maxim Nikulin <nikulin_at_gorodok.net>
Date: Fri, 13 Jan 2006 12:26:46 +0600

Hi,

I'm confused with TProfile::Scale method. I expected that bin errors are scaled with the same factor as mean values. I found that TProfile::Scale is implemented using TProfile::Add method and cvs log says:

...

revision 1.64
date: 2005/08/09 10:52:20; author: brun; state: Exp; lines: +59 -26
...

-In the operation functions Add, Divide, Multiply with multiplication   coefficients c1,c2, do not use c1*c1 or c2*c2 when computing   the resulting errors, but consider c1 and c2 like weigths as it is done   in the Fill functions. (Thanks Gero Flucke for this remark)
...

It seems reasonable for TProfile::Add, but shouldn't the Scale function use squared factor for error calculation? Let's imagine that I want to compare 2 profiles:

{

    p1 = new TProfile("p1", "p1", 10, 0, 10);

    p1->SetLineColor(kBlue);
    p1->Fill(1.5, 1);
    p1->Fill(1.5, 2);

    p2 = new TProfile("p2", "p2", 10, 0, 10);

    p2->SetLineColor(kRed);
    p2->Fill(3.5, 2);
    p2->Fill(3.5, 4);

    p2->Scale(0.5);

    p2->Draw();
    p1->Draw("same");
}

Are there any arguments why the points have different errors?

-- 
Maxim Nikulin

Received on Fri Jan 13 2006 - 07:26:58 MET