LauGaussPdf.cc

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// Copyright University of Warwick 2006 - 2013.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

// Authors:
// Thomas Latham
// John Back
// Paul Harrison

#include <iostream>
#include <vector>
using std::cout;
using std::cerr;
using std::endl;
using std::vector;

#include "TMath.h"
#include "TSystem.h"

#include "LauConstants.hh"
#include "LauGaussPdf.hh"

ClassImp(LauGaussPdf)


LauGaussPdf::LauGaussPdf(const TString& theVarName, const vector<LauAbsRValue*>& params, Double_t minAbscissa, Double_t maxAbscissa) :
        LauAbsPdf(theVarName, params, minAbscissa, maxAbscissa),
        mean_(0),
        sigma_(0)
{
        // Constructor for the Gaussian PDF.
        //
        // The parameters in params are the mean and the sigma (half the width) of the gaussian.
        // The last two arguments specify the range in which the PDF is defined, and the PDF
        // will be normalised w.r.t. these limits.

        mean_ = this->findParameter("mean");
        sigma_ = this->findParameter("sigma");

        if ((this->nParameters() != 2) || (mean_ == 0) || (sigma_ == 0)) {
                cerr<<"ERROR in LauGaussPdf constructor: LauGaussPdf requires 2 parameters: \"mean\" and \"sigma\"."<<endl;
                gSystem->Exit(EXIT_FAILURE);
        }

        // Cache the normalisation factor
        this->calcNorm();
}

LauGaussPdf::~LauGaussPdf() 
{
        // Destructor
}

void LauGaussPdf::calcLikelihoodInfo(const LauAbscissas& abscissas)
{
        // Check that the given abscissa is within the allowed range
        if (!this->checkRange(abscissas)) {
                gSystem->Exit(EXIT_FAILURE);
        }

        // Get our abscissa
        Double_t abscissa = abscissas[0];

        // Get the up to date parameter values
        Double_t mean = mean_->value();
        Double_t sigma = sigma_->value();

        // Calculate the value of the Gaussian for the given value of the abscissa.
        Double_t arg = abscissa - mean;

        Double_t exponent(0.0);
        if (TMath::Abs(sigma) > 1e-10) {
                exponent = -0.5*arg*arg/(sigma*sigma);
        }

        Double_t value = TMath::Exp(exponent);
        this->setUnNormPDFVal(value);

        // if the parameters are floating then we
        // need to recalculate the normalisation
        if (!this->cachePDF() && !this->withinNormCalc() && !this->withinGeneration()) {
                this->calcNorm();
        }

}

void LauGaussPdf::calcNorm() 
{
        // Get the up to date parameter values
        Double_t mean = mean_->value();
        Double_t sigma = sigma_->value();

        // Calculate the normalisation of the gaussian and cache it.
        Double_t scale = LauConstants::root2*sigma;
        Double_t norm(0.0);

        if (TMath::Abs(sigma) > 1e-10) {
                norm = LauConstants::rootPiBy2*sigma*(TMath::Erf((this->getMaxAbscissa() - mean)/scale) - TMath::Erf((this->getMinAbscissa() - mean)/scale));
        }

        this->setNorm(norm);
}

void LauGaussPdf::calcPDFHeight(const LauKinematics* /*kinematics*/)
{
        if (this->heightUpToDate()) {
                return;
        }

        // Get the up to date parameter values
        Double_t mean = mean_->value();

        LauAbscissas maxPoint(1);
        maxPoint[0] = mean;

        // Calculate the PDF height for the Gaussian function.
        if (mean>this->getMaxAbscissa()) {
                maxPoint[0] = this->getMaxAbscissa();
        } else if (mean<this->getMinAbscissa()) {
                maxPoint[0] = this->getMinAbscissa();
        }
        this->calcLikelihoodInfo(maxPoint);

        Double_t height = this->getUnNormLikelihood();
        this->setMaxHeight(height);
}