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====== DaVinci Example ======

This example creates a simple selection for J/psi -> mu+ mu- using the Particle Selection Framework (i.e. CombineParticle). It is a simplified version of the algorithm described in [[https://twiki.cern.ch/twiki/bin/view/LHCb/DaVinciTutorial4 | DaVinciTutorial4]].


===== Preparations =====
  * login to **lxplus**
  * make sure you have a [[https://lhcb.physik.uzh.ch/grid:grid | Grid]]-Certificate
  *

===== Create Python Configuration =====

<code python myOptions.py>
from Gaudi.Configuration import *                                          
from GaudiKernel.SystemOfUnits import MeV, GeV
from Configurables import CombineParticles
from PhysSelPython.Wrappers import Selection, SelectionSequence, DataOnDemand

# prepare input data
_muons = DataOnDemand('_stdLooseMuons', Location = 'StdLooseMuons')

# create algorithm
myalg = CombineParticles("myalg")

# define decay and cuts
myalg.DecayDescriptor = "J/psi(1S) -> mu+ mu-"
myalg.CombinationCut = "ADAMASS('J/psi(1S)')<30*MeV"
myalg.MotherCut = "(VFASPF(VCHI2/VDOF)<10)"

# add plots to algorithm
from Configurables import LoKi__Hybrid__PlotTool as PlotTool
myalg.HistoProduce = True
myalg.addTool ( PlotTool ( 'DaughtersPlots' ) )
myalg.DaughtersPlots.Histos = {
   'P'  : ('momentum' , 0*GeV ,30*GeV) ,
   'M'  : ('mass'     ,0*GeV,1*GeV)
   }
myalg.addTool( PlotTool ( "MotherPlots" ) )
myalg.MotherPlots.Histos = {
   "P"  : ('momentum',0*GeV,100*GeV) ,
   "M"  : ('mass',0*GeV,4*GeV)
   }

# create selection
# Selection needs to be defined after all changes to the Algorithm
LooseJpsi2MuMu = Selection("seqLooseJPsi2MuMu", Algorithm = myalg, RequiredSelections =[ _muons ])

# start selection sequence
mySeq = SelectionSequence("mySeq", TopSelection = LooseJpsi2MuMu)

# configure the application.
from Configurables import DaVinci
DaVinci().UserAlgorithms = [ mySeq.sequence() ]
DaVinci().HistogramFile  = "histograms.root"    # Histogram file
DaVinci().EvtMax         = 1000                  # Number of events to loop over
DaVinci().DataType       = "MC09"               # Default anyway
DaVinci().Simulation     = True                 # It's MC
</code>

For more details about the names used in the DecayDescriptor, [[davinci:particletable | look at the ParticleTable]]. 
For a list of availbale funtors for CombinationCut and MotherCut, [[loki:lists | check the Loki references]].

=====Running=====
  * Set environment for Ganga
<code>SetupProject Ganga</code>

  * maybe you need to create a new config file
<code>ganga -g</code>

  * start
<code>ganga</code>

  * prepare job
<code python>
t = JobTemplate( application = DaVinci( ))
t.application.optsfile = File( "~/example/myOptions.py" )
</code>

  * add input data
<code python>
t.inputdata = browseBK()
# select MC / MC09 / Beam5TeV-VeloClosed-MagDown-Nu1 / MC09-Sim03Reco02-withTruth / 24142000 / DST
# you could instead use an python option file with the data locations 
# (see below on how to generate one)
#t.application.optsfile.append(  File( "~/example/myOptions.py" )  )
# the Ganga-Manual marks this as depreciated
</code>

  * create a job and run it
<code python>
j = Job( t, backend = Interactive() )
j.submit()
</code>


==== Running outside Ganga (locally)====
=== Prepare Data Files ===
  * run the Bookkeeping-GUI
<code>lhcb_bkk</code>
  * select 

<file>MC / MC09 / Beam5TeV-VeloClosed-MagDown-Nu1 / MC09-Sim03Reco02-withTruth / 24142000 / DST</file>

  * double-click on **Nb of Files/Events** and select all files

  * click **Advanced Save**
  * give Filename (e.g. "myFiles.py"), select **PFN(s)** and **CERN**
  * click **save**

=== Run ===
<code>
SetupProject DaVinci
gaudirun.py myOptions.py myFiles.py
</code>


===== Looking at the output =====
The Algorithm creates a file called histograms.root. 
  * If run with gaudirun.py it should be in the working directory. 
  * If run with ganga it can be found at **~/gangadir/workspace/<username>/LocalAMGA/<jobNr>/output/**
Start root and have a look at the histograms.

===== More Info =====
You can find more info at following locations:
  * [[ganga:ganga | Ganga]] 
  * [[davinci:davinci | DaVinci]]
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