Problem drawing a tree leave

ROOT
1

Again, another of my questions…

I have a root file that seems to be ok. then do the following:

root [0] TFile file("trouble.root");
root [1] TNtupleD* tuple = (TNtupleD*) gROOT->FindObject("angRes");
root [2] tuple->Draw("theta_theo");

And get pure garbage in the canvas (all entries should be in the same bin, nothing fancy. On the other hand, if I do

root [0] TFile file("trouble.root");
root [1] TNtupleD* tuple = (TNtupleD*) gROOT->FindObject("angRes");
root [2] tuple->Draw("theta - theta_theo");

It gives me the result I really want so I’m happy, but with the question: “what went wrong???”

I’m attaching the file and a screenshot of the canvas. I’m using Root 4.02/00, built from source, running on SuSE 9.2, gcc version 3.3.4

2

Your files are not yet available. We would need them in order to provide any insight.

Cheers,
Philippe.

3

oops, here they go.

The funny thing is that the canvas shows the right average value and a very small deviation, as it should, but it doesn’t show the right plot. With another file I wasn’t lucky enough to get the right result by plotting the difference but still the canvas was showing the right average. I hope this is simple to solve.

Javier
drawing_issue.tar.gz (18.9 KB)

4

I changed the TNtupleD by TNtuple and it seems to work fine.

5

Hi,

This is a problem of numerical stability. Since you have a series of double which have approximavely the value 20, TTree::Draw is trying to give you have much precision as possible. So in this case it dimension the histogram to range from 1.99999999999998690e+001 to 1.99999999999999930e+001
with 100 bins.
You can solve the problem by pre-dimensions the histogram, for example:

Cheers,
Philippe.

6

ah!

right. I couldn’t read the labels, I guess because they were crowded. That also explains why when I cast the numbers into floats it works.

Thanks