Using CRAB to generate MonteCarlo events

In order to generate MC events with CRAB it is sufficient to indicate the dataset parameter as none:

[CMSSW]
datasetpath = none

Random numbers

Unless the user supplies the settings to increment/preserve seeds, which are there to produce repeatability, each job gets a random set of random seeds and thus events should be unique. To increment/preserve seeds, use the CRAB configuration parameters increment_seeds and preserve_seeds respectively. A short explanation on how to use these configuration parameters can be found in the CRAB Online Manual.

How to generate different event identifiers

If you want different runs for different sets of jobs, you have to set the run number yourself in the CMSSW configuration file like explained in section How to set run number in CMSSW below. Crab (from the 2.7.1 series) doesn't have parameters that act on the run number, but instead it allows to work on the lumisection. Since an event is identified by a triple <run, lumi, event number>, incrementing the lumi ensures that there are not duplicate events, even if the run and the event number remain constants. Setting the parameter first_lumi under [CMSSW] section, the first job will generate events with this lumi section number and subsequent jobs will increment the lumi section number. For more information on how to use the first_lumi parameter, see this item description in the CRAB Online Manual.

How to add more data to a previous generation run

Generating another set of jobs with an increased first_lumi is the correct thing to do.

How to set run number in CMSSW

Your config file should look like this:

  RandomNumberGeneratorService = cms.Service(

     "RandomNumberGeneratorService",

     # This is to initialize the random engine of the source
     generator = cms.PSet(
         initialSeed = cms.untracked.uint32(123456789),
         engineName = cms.untracked.string('TRandom3')
     ),

     # This is to initialize the random engines used for  Famos
     VtxSmeared = cms.PSet(
         initialSeed = cms.untracked.uint32(123456789),
         engineName = cms.untracked.string('TRandom3')
     ),


....

For furter details refer to this HN: https://hypernews.cern.ch/HyperNews/CMS/get/crabFeedback/3075/1/1/1/1/1/1/1/1/2.html

-- MarcoCalloni - 14-Apr-2010

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Topic revision: r6 - 2014-04-24 - AndresTanasijczuk
 
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