Random Numbers in GAUDI

1
Random Numbers in GAUDI

• Requirements
• Interface
• Usage

2
Requirements

• Distinguish between generator and distribution
• Flexibility
• Change the random number generator if necessary
• No need to change user code
• Generate any distribution using a single
  generator
• Reproducibility
• Start simulation at any point
• Initialization at each event
• Set the seed necessary to restart

3
Architecture
RndmGenSvc
owns initializes
Distribution Gauss
owns
uses
RndmGen
RndmEngine
4
Interface

• Generator Interface
• Service Interface
• There is a wrapper to simplify the code

/// Single shot returning single random
number virtual double shoot() const 0 ///
Multiple shots returning vector with random
number virtual StatusCode shootArray(
stdvectorltdoublegt array,
long howmany,
long start 0) const 0
/// Retrieve a valid generator from the
service. virtual StatusCode generator( const
IRndmGenParam par,
IRndmGen refpGen) 0
5
IRndmGenParam ???!!!

• Defines the shape of the generated distribution
• RndmBit()
• RndmFlat(double mi, double ma)
• RndmGauss(double mean, double sigma)
• RndmPoisson(double mean)
• RndmBinomial(long n, double p)
• RndmExponential(double mean)
• RndmChi2(long n_dof)
• RndmBreitWigner(double mean, double gamma)
• RndmBreitWignerCutOff (mean, gamma, cut-off)
• RndmLandau(double mean, double sigma)
• RndmDefinedPdf(const stdvectorltdoublegt pdf,
  long intpol)

See Gaudi/RandmGenSvc/RndmGenerators.h
6
Local Usage

• I just need a number how do I get it quickly ?
• Needs to be initialized for every event
• There are some useful examples, but not always!

include Gaudi/RandmGenSvc/RndmGenerators.h
RndmNumbers gauss(randSvc(),
RndmGauss(0.5,0.2)) if ( gauss )
IHistogram1D his histoSvc()-gtbook() for (
long i 0 i lt 5000 i )
his-gtfill(gauss(), 1.0)
7
Global Usage

• Get the generator once, then keep it!
• In the header file or your algorithm
• In myAlgorithminitialize
• In myAlgorithmexecute use it!

include Gaudi/RandmGenSvc/RndmGenerators.h cla
ss myAlgorithm public Algorithm
RndmNumbers m_gaussDist
StatusCode sc m_gaussDist.initialize( randSvc(
), RndmGauss(0.5,0.2))
his-gtfill(m_gaussDist(), 1.0)
8
Dos and Donts

• The interface allows to retrieve a bunch of
  random numbers
• Do not keep numbers across events
  Reproducibility!
• Often caching does more harm than it helps
• If there is a performance penalty, better find
  another solution
• Use the wrapper
• its easier
• Do not access the RndmEngine directly
• Do not manipulate the engine Reproducability

9
Summary

• Random generator is flexible
• Many distributions possible
• Easy to use
• Wrapper is straight forward
• Wrapper can be used with STL operator()
• Allows to be initialized by the framework in a
  way to ensure reproducability
• As long as everyone sticks to the rules

10
GAUDI Shared Libraries

• LD_LIBRARY_PATH Its a mess!
• String becomes too long for some shells
• Load Shared libraries by environment
• requirements
• set GaudiSvcShr "GAUDISVCROOT/BINDIR/libGau
  diSvc
• jobOptions
• ApplicationMgr.DLLs GaudiSvc
• LD_LIBRARY_PATH becomes much shorter
• Contains only path to images needed to start the
  program
• Better control over usage of modules

11
GAUDI CMT requirements

• Include path
• Instead of
• include_dirs (GAUDISVCROOT)
• Do the following for component libraries
• include_path none
• Or for public libraries
• include_path (GAUDISVCROOT)
• This shortens the compile statement(s)
  dramatically