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 "TH1F" 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) is an integer which identifies the number of "bins" the histogram will use to store information. The Fourth parameter (-0.5) is a real number identifying 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();