#include <SimpleHistogramGenerator.h>

Public Member Functions
int	binarySearch (const int &n, const std::vector< double > &array, const double &value) const
double	generate () const
	The random generation.
	SimpleHistogramGenerator (TH1 histo, const RandomEngine engine)
virtual	~SimpleHistogramGenerator ()
	Default destructor.
Private Attributes
double	binWidth
std::vector< double >	integral
	Integral.
TH1 *	myHisto
	Pointer to the histogram.
int	nBins
	Number of bins.
double	nEntries
	Number of entries.
const RandomEngine *	random
TAxis *	theXaxis
	the axis
double	xMax
double	xMin

Detailed Description

Definition at line 21 of file SimpleHistogramGenerator.h.

Constructor & Destructor Documentation

SimpleHistogramGenerator::SimpleHistogramGenerator	(	TH1 *	histo,
		const RandomEngine *	engine
	)

Constructor that perform the necessary integration and inversion steps xmin and xmax are the generation bounds, n is the internal table size and iter is the number of iterations for the numerical part.

Definition at line 8 of file SimpleHistogramGenerator.cc.

References i, integral, nBins, and nEntries.

                                                                                          :
  random(engine), 
  myHisto(histo),
  theXaxis(histo->GetXaxis()),
  nBins(theXaxis->GetNbins()),
  xMin(theXaxis->GetXmin()),
  xMax(theXaxis->GetXmax()),
  binWidth((xMax-xMin)/(float)nBins)
{
  integral.push_back(0.);
  for ( int i=1; i<=nBins; ++i )
    integral.push_back(integral[i-1]+histo->GetBinContent(i));
  integral.push_back(integral[nBins]);
  nEntries = integral[nBins+1];
  for ( int i=1; i<=nBins; ++i )
    integral[i] /= nEntries;

}

virtual SimpleHistogramGenerator::~SimpleHistogramGenerator ( ) [inline, virtual]

Default destructor.

Definition at line 31 of file SimpleHistogramGenerator.h.

{}

Member Function Documentation

int SimpleHistogramGenerator::binarySearch	(	const int &	n,
		const std::vector< double > &	array,
		const double &	value
	)		const

Definition at line 44 of file SimpleHistogramGenerator.cc.

Referenced by generate().

{
   // Binary search in an array of n values to locate value.
   //
   // Array is supposed  to be sorted prior to this call.
   // If match is found, function returns position of element.
   // If no match found, function gives nearest element smaller than value.

   int nabove, nbelow, middle;
   nabove = n+1;
   nbelow = 0;
   while(nabove-nbelow > 1) {
      middle = (nabove+nbelow)/2;
      if (value == array[middle-1]) return middle-1;
      if (value  < array[middle-1]) nabove = middle;
      else                          nbelow = middle;
   }
   return nbelow-1;
}

double SimpleHistogramGenerator::generate ( ) const

The random generation.

Definition at line 29 of file SimpleHistogramGenerator.cc.

References binarySearch(), binWidth, RandomEngine::flatShoot(), integral, nBins, random, ExpressReco_HICollisions_FallBack::x, and xMin.

                                         {

  // return a random number distributed according the histogram bin contents.
  // NB Only valid for 1-d histograms, with fixed bin width.

   double r1 = random->flatShoot();
   int ibin = binarySearch(nBins,integral,r1);
   double x = xMin + (double)(ibin) * binWidth;
   if (r1 > integral[ibin]) x +=
      binWidth*(r1-integral[ibin])/(integral[ibin+1] - integral[ibin]);
   return x;

}