Frequently Asked Questions

Please have a look at this list before asking for help on the ROOT forum.


Prerequisites for building ROOT from source.

To successfully build ROOT a number of prerequisite packages must be installed. Check the prerequisites page for the list of packages needed for your platform.

Why fill patterns and hatches disappear in PostScript output?

See the WARNING section at the end of this page.

Subversion can not connect to server.

Try adding the line: 

http-library=serf
to ~/.subversion/servers

How to use ROOT libraries in Xcode on Mac OS X?

The easiest way is to use cmake and let it create the Xcode project, this has the advantage that the dictionaries are created automatically. With the two files CMakefile.txt, and FindROOT.cmake which set the ROOT needed variables, one can compile and link ones own code. An example from the ROOT Event example (found in root/test) is attached. Just un-tar the attached file and run:

cmake -G  Xcode ./

This will create an Xcode project Event.xcodeproj which can be opened and used by Xcode.

How to check is a file is already open? 

   if (gROOT->GetListOfFiles()->FindObject(filename) ) {
      // do not open the file
   } else {
      // open the file
   }

Changing the Displayed Title in Canvas.

Disable the title and add yourself your own title with a TPaveLabel: 

   gStyle->SetOptTitle(0);
   TPaveLabel *title = new TPaveLabel(.11,.95,.35,.99,"new title","brndc");
   title->Draw();

How to change the automatic plot title produced when a tree is drawn?

It is enough to change the title of the histogram htemp: 

tree.Draw("x:y");
htemp.SetTitle("New Title");

How to draw several TGraph in one common axis system?

Use TMultiGraph.

How do I start PROOF?

Type at the ROOT prompt:

   root [0] TProof::Open("")
Some or all windows don't get displayed when ROOT is running on a remote computer.

You probably used ssh to connect to the remote computer. You need to specify the option "-Y" which turns on trusted X11 forwarding.