A QuickStart Guide to using the Hall A C++ Analyzer


Building and Installing

Don't build the Analyzer yourself! Just log into the Hall A counting house analysis computers (adaql3-5, adaqs2-3), e.g. as adaq, and type
Usually, all you have left to do is to set up an appropriate database for the data you wish to analyze.

If you do want to (or need to) build the program yourself, here are brief instructions.

The distribution is by default configured for Linux. To change to the Solaris/CC5 environment see explanation in the Makefile.

Before compiling, make sure that your have set ROOTSYS correctly and $ROOTSYS/bin is in your PATH.

WARNING: Some bugs have been observed when using the analyzer with versions of ROOT prior to 3.02-00. It is recommended to version 3.02-07 or later. Also, it is important to be certain that ROOT was compiled with the same (or at least compatible) version of gcc you are planning to use. On the ifarml machines, issue the commands

  use root/3.05-07
  use gcc/3.2.3
to configure ROOT and set the PATH.

To compile, run the Makefile with GNU make (tested with make 3.78-1). Usually, you just need to type "gmake".

Before running, it is useful to set the appropriate environment variables such that the executables, libraries, and databases are found. This can be done (while in the analyzer directory) as:

        export LD_LIBRARY_PATH=`pwd`:$ROOTSYS/lib:$LD_LIBRARY_PATH
	export PATH=`pwd`:$PATH
	export DB_DIR=`pwd`/DB
	setenv PATH `pwd`:$PATH
	setenv DB_DIR `pwd`/DB
(i.e. make sure the current directory is in the LD_LIBRARY_PATH and PATH, as well setting the DB_DIR path).

To start the analyzer, just execute:

 > analyzer
and you should get the prompt:

Running the Analyzer

In the examples directory are files to demonstrate how to use the analyzer. They are:
  doit.C             - Drives the setup.C macro and displays some results.
                       This is what might normally be done by hand.

  setup.C            - example analysis macro (uses next 2 files)
  cuts_example.def   - text file which defines many example cuts
  output_example.def - text file specifying global variable to output
                       into the 'T' tree.
To start the analyzer to use the macro, you can do at the shell prompt:
    analyzer doit.C
or, if done in separate steps:
    .x doit.C        # from inside the analyzer

Global Variables

Each detector, physics module, or apparatus can contain and report "global variables" which can be used to define cuts, evaluate formulas, and fill histograms. A complete list can be reported after starting and initializing the analyzer via:
    gHaVars->Print()        //   and
where a pattern to match the variable name to may be given: Example:

	OBJ: THaVar     nev     Event number
	OBJ: THaVar     R.tr.n  Number of tracks
	OBJ: THaVar     R.tr.x  Track x coordinate (m)
	OBJ: THaVar     R.tr.y  Track x coordinate (m)

	OBJ: THaVar     R.s1.lt TDC values left side
	(Float_t*)[*6]  0  1.59e+03  0  0  0  0
	OBJ: THaVar     R.s1.lt_c       Corrected TDC values left side
	(Float_t*)[*6]  0  2.4e+03  0  0  0  0
	OBJ: THaVar     R.s1.la ADC values left side
	(Float_t*)[*6]  0  2.09e+03  0  0  0  0
	OBJ: THaVar     R.s1.la_p       Corrected ADC values left side
	(Float_t*)[*6]  0  1.62e+03  0  0  0  0
	OBJ: THaVar     R.s1.la_c       Corrected ADC values left side
	(Float_t*)[*6]  0  848  0  0  0  0

Analysis Cuts

Cuts can steer the analysis, as well as perform basic accounting of event topologies. The cuts are defined in a user-specified file, eg:
The cuts are divided into "Block"'s, with each block corresponding to a stage in the analysis and the stage that the cut is evaluated after. The format is each line has two entries separated by white space. Comments start at a '#' character and continue through the line.

A special cut named "Block-name"_master can be defined, and if false causes the analysis to stop processing the current event, and move on to the next event.

Example (contents of cuts definition file):

    Block: RawDecode

	evtyp1            g.evtyp==1      # Event type 1 (=HRSR main trigger)
	evtyp3            g.evtyp==3      # Event type 3 (=HRSL main trigger)
	poshel            g.helicity==1
	neghel            g.helicity==-1
	goodhel           poshel||neghel
	evprime           evtyp1||evtyp3
	RawDecode_master  evprime         # only decode primary trigger events

Tree Output

Output from the analyzer can be saved in a couple of basic methods. The simplest is to use the THaAnalyzer::SetOdefFile(const char* name) method. eg:
This file defines a list of global variables to save for each event, as well as formulas to evaluate and histograms to fill. For every event, the Global Variables can be processed and saved to a ROOT TTree object (very similar to an HBook Ntuple in this implementation).

Example (contents of output definition file):

        block L.tr.*       # Pattern matching from global variables.
			   # All L-arm tracking variables
	variable   L.vdc.u2.nclust  # Single global variable
	variable   R.s1.lt          # Array of values R.s1.lt[i]
# for i = 0,1,...Ndata.R.s1.lt

Examining the Output

After creating the tree, you can interactively examine the results of the filled histograms with TTree::Draw (command line interface) or TTree::StartViewer (GUI interface). The names of the entries correspond to what was specified in the output definition file.

Example (at the analyzer [ ] prompt):

    T->Draw("L.tr.n");                // draw number of tracks in Left arm
    T->Draw("R.tr.tg_dp","abs(R.tr.tg_dp)<.1");  // HRS-R delta-p with cut
    T->StartViewer();                 // start interactive GUI Tree-viewer
For more information on drawing/processing trees, you are referred to the example scripts and the ROOT documentation (http://root.cern.ch).

Exiting/Resuming a Session

Type ".q" to quit the analyzer. The Tree can be accessed later by re-opening the file via (assuming the output file is "Afile.root"):
    analyzer Afile.root
or, from within the analyzer:
    TFile* oldfile = new TFile("Afile.root");
Robert Feuerbach <feuerbac@jlab.org>
Last modified: Mon Nov 17 12:54:25 EST 2003