About binning a histogram

[Carlos]

Hi. I’m trying to fill a histograms with some data. The code I have is similar to this example. Suppose I have some data of the function x^2 (real problem is no with a function but with measured data, so I can’t use graph instead histogram)

TH1D *event;
event = new TH1D ( "Event example" , "event", 1000, 0, 1000); 
for(int i=1; i<1000; i++){
      event->Fill((x-500)^2)
    }

When I see the histogram I don’t see the parabola but other thing. So the I have tried to make

for(int i=1; i<1000; i++){
      event->Fill(i,(x-500)^2)
    }

The problem now is that in addition to the parabola I want, I obtain other lines that I don’t know how to delete them. Can anyone help me?

[yus]

Hi Carlos,

the (x-500)^2 does not mean "(x-500) squared" in C++, pow(x-500, 2) does. After changing your piece of code into

TH1D *event;
event = new TH1D ( "Event example" , "event", 1000, 0, 1000);
for(int i=1; i<1000; i++){
    event->Fill(i, pow(i-500, 2));
}
event->Draw();

I ran it and got this:

Which lines are you talking about?

[Carlos]

Hi yus. Thank you for your answer. That’s not the problem. I wrote it wrong here but not in my code. The image you posted is what I want, but this is what I actually get:

As you can see there is the line that you obtained + undesired blue stuff.

[Wile_E_Coyote]

event->Draw("HIST");

[Carlos]

Hi. Still having some trouble:

[Wile_E_Coyote]

It seems to me that for some bins you call “Fill” twice.

[yus]

Hi,
can you post the entire code? It does not seem that you are running the code snippet from above: you had

event = new TH1D ( "Event example" , "event", 1000, 0, 1000);

, but in your screenshot the histogram goes up to 1100 - why?