TF ErrAna InClassLab

Start ROOT and Draw Histogram

Step 1

In this first lab your goal will be to start root and draw a histogram.

If you are on a Windows machine start the ROOT interpreter by double clicking on the Desctop icon which looks like a tree and says ROOT underneath it If you are on a Unix machine set the environmental variable ROOTSYS to point to the base subdirectory containing the ROOT files and start root with the command $ROOTSYS/bin/root. You can set the ROOTSYS environmental variable under the bash chell with the command

export ROOTSYS=path

where path identifies the location of the root base subdirectory. My ROOT base subdirectory is located at ~/src/ROOT/root so I would execture the following shell command

export ROOTSYS=~/src/ROOT/root

Step 2

Define a variable to contain the desired histogram

TH1F *Hist1=new TH1F("Hist1","Hist1",50,-0.5,49.5);

The above function "TH!F" has 5 parameters.

The first parameter "Hist1" create a name for the histogram. The second parameter gives the histogram a title. I usually set the name and title to the same variable name I use to store the histogram. This allows me to look up the variable name of the histogram when I double click on the histogram from the browser listing. The third parameter (50) identifies the number of "bins" which the histogram will use to store information. The Fourth parameter (-0.5) is the numerical value to be used for the lowest bin and the fifth parameter is the value for the highest bin.

 Hist1->Fill(10);

 Hist1->Draw();

[1] Forest_Error_Analysis_for_the_Physical_Sciences