Using MOFIA root trees
-Jim Musser, 11 September 2003.

I am carefully documenting each step as I learn to use MOFIA root
trees in order to produce a document designed to help others begin
simple histogramming.  Thanks are due to Blair for taking the time to
get me started.  It doesn't take long to produce simple plots.  I
encourage you to try this simple tutorial.

(The variables in the ROOT Tree are described at the top of the file
$MOFIA_USER/helixtree.f90 in your Mofia installation.)


I.   Enabling root tree production in MOFIA.

     A.  Add the following lines to your kcm file or enter them at the MOFIA
	 prompt.

	   Name RootTree
	   EnableRootTree = T
	   &

     B.  Use the executable "photo" which contains the required root
	 libraries not available in "mofia".  This will produce a file named
	 "tree[run number].root" that contains the root tree.


II.  Beginning a root session.  Note that entering "root" in a terminal on
     the cluster will bring up an old version of root that is used for photo.
     The old version is "buggy" according to more experienced users.
     Do the following to use the "preferred" executable (instructions
     from Konstantin Olchanski):

     Set ROOTSYS in your login script:
        > setenv ROOTSYS /twist/local/root.gcc32.new
     then start ROOT:
        > $ROOTSYS/bin/root -l

     (This dance avoids a mismatch between the ROOT executable and
     ROOT libraries accessed using ROOTSYS.)


III. Opening the tree in root.

     A.  At the prompt enter:
	 
	   new TBrowser

	 This produces a window labeled "ROOT Object Browser".

     B.  In the "ROOT Object Browser" window select the directory containing
	 your root tree file.  (Double click)

     C.  Select your root tree file, "tree[run number].root".  This will make
	 the tree available in the directory, "ROOT Files".

     D.  Select the directory "ROOT Files".  (Double click)

     E.  Select your root tree file, "tree[run number].root".  This reveals a
	 directory named "T;1"


IV.  Viewing variables.

     A.  Select the directory named "T;1".  This reveals a list of variables
	 next to leaf icons.

     B.  Select "Details" from the "View" pull-down menu.  Two columns are
	 given.  The first is the variable name.  The second, labeled "Title"
	 includes some additional information.  Dimensions of arrays are shown
	 in square brackets.  Variable type (I-integer, F-floating point) is
	 shown after a "/"


V.   Producing histograms.

     A.  Select the directory of your root tree file within "ROOT Files".  Right
	 click on the directory, "T", and select "StartViewer".  This will open
	 a window labeled "TreeViewer".

     [Method 1]
     B.  Double click on a variable name or it's leaf icon.
	 (Try "Event_m12width".)  Congratulations.  You have plotted your first
	 histogram in root.

     [Method 2]
     C.  Click and drag the variable to the "X:"  (Try "Track_ptot".)

     D.  Click on the graph icon in the bottom left corner of the "TreeViewer"
	 window.  Note that if you chose an array (like "Track_ptot") there is
	 no evidence that it is an array without consulting the detailed view we
	 saw earlier in the "ROOT Object Browser" window.  Root simply plots all
	 elements of the array unless given specific instructions otherwise (in
	 the tradition of PAW).

     E.  Right click on the variable name beside "X:" and select
	 "EditExpression".  Append the array element index within square
	 brackets to the end of the expression.  For example:

	   Track_ptot[Event_idktr]

	 Click "Done".  Click on graph icon.

     F.  Drag a second variable to the "Y:"  (Try "Track_costh" and edit the
	 expression to use element "Event_idktr".  Click on graph icon.  You
	 have now produced a two dimensional plot.


VI.  Adding cuts.

     Right click on scissors icon and select "EditExpression".  Enter
     "Selection" based on tree variables.  Such as:

       Event_idktr>-1

     Give the cut a name in the "Alias" box.  ie.

       decay_cut

     Click "Done" and graph icon.


VII. Manipulating plots.  There are many advanced features that control
     presentation.  Several of these are easily accessible with panels called
     from pull-down menus.

     A.  Right clicking on canvas will reveal one of several pull-down menus.  I
	 found the following:
	 1.  Canvas
	 2.  Title
	 3.  Histogram ("htemp" in my case)
	 4.  xaxis
	 5.  yaxis
	 6.  Frame
	 7.  Stats

     B.	 From the histogram pull-down menu choose "DrawPanel" or "FitPanel".

     C.  From the Edit pull-down menu choose "Editor".

     D.  Now play and have fun!