#include <GaussianTailNoiseGenerator.h>

Public Member Functions
	GaussianTailNoiseGenerator (CLHEP::HepRandomEngine &eng)

void	generate (int NumberOfchannels, float threshold, float noiseRMS, std::map< int, float > &theMap)

void	generate (int NumberOfchannels, float threshold, float noiseRMS, std::vector< std::pair< int, float > > &)

void	generateRaw (float noiseRMS, std::vector< double > &)

Protected Member Functions
double	generate_gaussian_tail (const double, const double)

int *	getRandomChannels (int, int)

Private Attributes
int	channel512_ [512]

int	channel768_ [768]

CLHEP::RandFlat	flatDistribution_

CLHEP::RandGaussQ	gaussDistribution_

CLHEP::RandPoissonQ	poissonDistribution_

Detailed Description

Generation of random noise on "numberOfChannels" channels with a given threshold. The generated noise :

corresponds to a Gaussian distribution of RMS = "noiseRMS"
is larger than threshold*noiseRMS.

Initial author : Veronique Lefebure 08.10.98
according to the FORTRAN code tgreset.F from Pascal Vanlaer
Modified by C. Delaere 01.10.09

Fills in a map < channel number, generated noise >

Definition at line 29 of file GaussianTailNoiseGenerator.h.

Constructor & Destructor Documentation

GaussianTailNoiseGenerator::GaussianTailNoiseGenerator ( CLHEP::HepRandomEngine & eng )

Definition at line 11 of file GaussianTailNoiseGenerator.cc.

References channel512_, channel768_, and i.

                                                                                  :
   gaussDistribution_(eng),
   poissonDistribution_(eng),
   flatDistribution_(eng)
 {
   // we have two cases: 512 and 768 channels
   // other cases are not allowed so far (performances issue)
   for(unsigned int i=0;i<512;++i) channel512_[i]=i;
   for(unsigned int i=0;i<768;++i) channel768_[i]=i;
 }

Member Function Documentation

void GaussianTailNoiseGenerator::generate	(	int	NumberOfchannels,
		float	threshold,
		float	noiseRMS,
		std::map< int, float > &	theMap
	)

Referenced by SiPixelDigitizerAlgorithm::add_noise(), and SiGaussianTailNoiseAdder::addNoise().

void GaussianTailNoiseGenerator::generate	(	int	NumberOfchannels,
		float	threshold,
		float	noiseRMS,
		std::vector< std::pair< int, float > > &	theVector
	)

Definition at line 54 of file GaussianTailNoiseGenerator.cc.

References benchmark_cfg::cerr, generate_gaussian_tail(), getRandomChannels(), i, poissonDistribution_, and query::result.

                                                                   {
   // Compute number of channels with noise above threshold
   // Gaussian tail probability
   gsl_sf_result result;
   int status = gsl_sf_erf_Q_e(threshold, &result);
   if (status != 0) std::cerr<<"GaussianTailNoiseGenerator::could not compute gaussian tail probability for the threshold chosen"<<std::endl;
   double probabilityLeft = result.val;  
   double meanNumberOfNoisyChannels = probabilityLeft * NumberOfchannels;
   int numberOfNoisyChannels = poissonDistribution_.fire(meanNumberOfNoisyChannels);
   if(numberOfNoisyChannels>NumberOfchannels) numberOfNoisyChannels=NumberOfchannels;
 
   // Compute the list of noisy channels
   theVector.reserve(numberOfNoisyChannels);
   float lowLimit = threshold * noiseRMS;
   int*  channels = getRandomChannels(numberOfNoisyChannels,NumberOfchannels);
   
   for (int i = 0; i < numberOfNoisyChannels; i++) {
     // Find random noise value
     double noise = generate_gaussian_tail(lowLimit, noiseRMS);
     // Fill in the vector
     theVector.push_back(std::pair<int, float>(channels[i], noise));
   }
 }

double GaussianTailNoiseGenerator::generate_gaussian_tail	(	const double	a,
		const double	sigma
	)

protected

Definition at line 127 of file GaussianTailNoiseGenerator.cc.

References flatDistribution_, gaussDistribution_, funct::log(), asciidump::s, mathSSE::sqrt(), v, and x.

Referenced by generate().

                                                                                     {
   /* Returns a gaussian random variable larger than a
    * This implementation does one-sided upper-tailed deviates.
    */
   
   double s = a/sigma;
   
   if (s < 1){
     /*
       For small s, use a direct rejection method. The limit s < 1
       can be adjusted to optimise the overall efficiency 
     */
     double x;
     
     do{
       x = gaussDistribution_.fire(0.,1.0);
     }
     while (x < s);
     return x * sigma;
     
   }else{
     
     /* Use the "supertail" deviates from the last two steps
      * of Marsaglia's rectangle-wedge-tail method, as described
      * in Knuth, v2, 3rd ed, pp 123-128.  (See also exercise 11, p139,
      * and the solution, p586.)
      */
     
     double u, v, x;
     
     do{
       u = flatDistribution_.fire();
       do{
     v = flatDistribution_.fire();
       }while (v == 0.0);
       x = sqrt(s * s - 2 * log(v));
     }
     while (x * u > s);
     return x * sigma;
   }
 }

void GaussianTailNoiseGenerator::generateRaw	(	float	noiseRMS,
		std::vector< double > &	theVector
	)

Definition at line 97 of file GaussianTailNoiseGenerator.cc.

References gaussDistribution_, and i.

                                                                             {
   // it was shown that a complex approach, inspired from the ZS case,
   // does not allow to gain much. 
   // A cut at 2 sigmas only saves 25% of the processing time, while the cost
   // in terms of meaning is huge.
   // We therefore use here the trivial approach (as in the early 2XX cycle)
   unsigned int numberOfchannels = theVector.size();
   for (unsigned int i = 0; i < numberOfchannels; ++i) {
     if(theVector[i]==0) theVector[i] = gaussDistribution_.fire(0.,noiseRMS);
   }
 }

int * GaussianTailNoiseGenerator::getRandomChannels	(	int	numberOfNoisyChannels,
		int	numberOfchannels
	)

protected

Definition at line 111 of file GaussianTailNoiseGenerator.cc.

References b, channel512_, channel768_, flatDistribution_, and j.

Referenced by generate().

                                                                                              {
   if(numberOfNoisyChannels>numberOfchannels) numberOfNoisyChannels = numberOfchannels;
   int* array = channel512_;
   if(numberOfchannels==768) array = channel768_;
   int theChannelNumber;
   for(int j=0;j<numberOfNoisyChannels;++j) {
     theChannelNumber = (int)flatDistribution_.fire(numberOfchannels-j)+j;
     // swap the two array elements... this is optimized by the compiler
     int b = array[j];
     array[j] = array[theChannelNumber];
     array[theChannelNumber] = b;
   }
   return array;
 }