M.Frank LHCb/CERN

Random Numbers in GAUDI

Requirements Interface Usage

M.Frank LHCb/CERNGAUDI

Requirements

Distinguish between generator and distribution

FlexibilityChange the random number generator if necessaryNo need to change user codeGenerate any distribution using a single generator

ReproducibilityStart simulation at any point

Initialization at each eventSet the seed necessary to restart

M.Frank LHCb/CERNGAUDI

Architecture

RndmGenSvc

RndmGen RndmEngine

Distribution:Gauss

owns & initializes

usesowns

M.Frank LHCb/CERNGAUDI

Interface

/// Single shot returning single random numbervirtual double shoot() const = 0;

/// Multiple shots returning vector with random numbervirtual StatusCode shootArray( std::vector<double>& array, long howmany, long start = 0) const = 0;

Generator Interface

Service Interface

There is a wrapper to simplify the code

/// Retrieve a valid generator from the service.virtual StatusCode generator( const IRndmGen::Param& par, IRndmGen*& refpGen) = 0;

M.Frank LHCb/CERNGAUDI

IRndmGen::Param ???!!!

Defines the shape of the generated distributionRndm::Bit()Rndm::Flat(double mi, double ma)Rndm::Gauss(double mean, double sigma)Rndm::Poisson(double mean)Rndm::Binomial(long n, double p)Rndm::Exponential(double mean)Rndm::Chi2(long n_dof)Rndm::BreitWigner(double mean, double gamma)Rndm::BreitWignerCutOff (mean, gamma, cut-off) Rndm::Landau(double mean, double sigma)Rndm::DefinedPdf(const std::vector<double>& pdf, long intpol)See Gaudi/RandmGenSvc/RndmGenerators.h

M.Frank LHCb/CERNGAUDI

I just need a number how do I get it quickly ?

Needs to be initialized for every eventThere are some useful examples, but not always!

#include “Gaudi/RandmGenSvc/RndmGenerators.h” Rndm::Numbers gauss(randSvc(), Rndm::Gauss(0.5,0.2)); if ( gauss ) { IHistogram1D* his = histoSvc()->book(); for ( long i = 0; i < 5000; i++ ) his->fill(gauss(), 1.0); }

Local Usage

M.Frank LHCb/CERNGAUDI

Get the generator once, then keep it!In the header file or your algorithm:

In myAlgorithm::initialize

In myAlgorithm::execute: use it!

StatusCode sc = m_gaussDist.initialize(randSvc(), Rndm::Gauss(0.5,0.2));

Global Usage

#include “Gaudi/RandmGenSvc/RndmGenerators.h”

class myAlgorithm : public Algorithm { Rndm::Numbers m_gaussDist;

his->fill(m_gaussDist(), 1.0);

M.Frank LHCb/CERNGAUDI

Dos and Don’ts

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 it’s easier

Do not access the RndmEngine directly Do not manipulate the engine: Reproducability

M.Frank LHCb/CERNGAUDI

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

M.Frank LHCb/CERNGAUDI

GAUDI: Shared Libraries

LD_LIBRARY_PATH: It’s a mess! String becomes too long for some shells Load Shared libraries by environment requirements:

set GaudiSvcShr "${GAUDISVCROOT}/${BINDIR}/libGaudiSvc”

jobOptions: ApplicationMgr.DLLs += {“GaudiSvc”};

LD_LIBRARY_PATH becomes much shorterContains only path to images needed to start the

program

Better control over usage of modules

M.Frank LHCb/CERNGAUDI

GAUDI: CMT requirements

Include path Instead of

include_dirs $(GAUDISVCROOT)

Do the following for component librariesinclude_path none

Or for public libraries:include_path $(GAUDISVCROOT)

This shortens the compile statement(s) dramatically