/data/refman/pasoursint/CMSSW_5_2_7_hltpatch2/src/SimRomanPot/SimFP420/src/GaussNoiseProducerFP420.cc

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// File: GaussNoiseProducerFP420.cc
// Date: 12.2006
// Description: GaussNoiseFP420 for FP420
// Modifications: 
#include "SimRomanPot/SimFP420/interface/GaussNoiseProducerFP420.h"
#include "CLHEP/Random/RandPoisson.h"
#include "CLHEP/Random/RandFlat.h"
#include <gsl/gsl_sf_erf.h>
#include <gsl/gsl_sf_result.h>
#include <gsl/gsl_randist.h>
#include <gsl/gsl_rng.h>

extern "C"   float freq_(const float& x);   
extern "C"   float gausin_(const float& x);

void GaussNoiseProducerFP420::generate(int NumberOfchannels, 
                                       float threshold, 
                                       float noiseRMS, 
                                       std::map<int,float, std::less<int> >& theMap )
{
  
  // estimale mean number of noisy channels with amplidudes above $AdcThreshold$
  
  // Gauss is centered at 0 with sigma=1
  // Gaussian tail probability higher threshold(=5sigma for instance):
  gsl_sf_result result;
  int status = gsl_sf_erf_Q_e(threshold, &result);
  //MP 
  //  if (status != 0) throw DetLogicError("GaussNoiseProducerFP420::could not compute gaussian tail probability for the threshold chosen");
  if (status != 0) std::cerr<<"GaussNoiseProducerFP420::could not compute gaussian tail probability for the threshold chosen"<<std::endl;
  float probabilityLeft = result.val;
  
  // with known probability higher threshold compute number of noisy channels distributed in Poisson:
  float meanNumberOfNoisyChannels = probabilityLeft * NumberOfchannels;
  int numberOfNoisyChannels = CLHEP::RandPoisson::shoot(meanNumberOfNoisyChannels);
  
  // draw noise at random according to Gaussian tail
  
  // initialise default gsl uniform generator engine
  static gsl_rng * mt19937 = gsl_rng_alloc (gsl_rng_mt19937);
  
  float lowLimit = threshold * noiseRMS;
  for (int i = 0; i < numberOfNoisyChannels; i++) {
    
    // Find a random channel number    
    int theChannelNumber = (int) CLHEP::RandFlat::shootInt(NumberOfchannels);
    
    // Find random noise value: random mt19937 over Gaussian tail above threshold:
    float noise = gsl_ran_gaussian_tail(mt19937, lowLimit, noiseRMS);
    
    // Fill in map
    theMap[theChannelNumber] = noise;
    
  }
}