Gabriele Cosmo
99 lines
3.7 KiB
C++
99 lines
3.7 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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////////////////////////////////////////////////////////////////////////////////
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// //
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// File: G4BetaSpectrumSampler.cc //
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// Author: D.H. Wright //
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// Date: 21 November 2022 //
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// Description: samples a spectrum which is a piece-wise linear function of //
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// energy. The CDF is calculated by trapezoidal integration //
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// and within bins the line y = mx + b is sampled. //
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// //
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////////////////////////////////////////////////////////////////////////////////
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#include "G4BetaSpectrumSampler.hh"
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G4BetaSpectrumSampler::
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G4BetaSpectrumSampler(const G4double* aPDF, G4int pdfSize, G4double e)
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{
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pdf.resize(pdfSize);
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nBins = pdfSize-1;
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cdf.resize(nBins);
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eEnd = e;
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lowerBinEdge = 0;
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upperBinEdge = 1;
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for (G4int i = 0; i < pdfSize; i++) pdf[i] = aPDF[i];
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// Caclulate binwise CDF using trapezoidal integration
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G4double sum = pdf[0]/2.;
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for (G4int i = 1; i < pdfSize; i++) {
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sum += pdf[i];
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cdf[i-1] = sum - pdf[i]/2.;
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}
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}
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G4double G4BetaSpectrumSampler::shoot()
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{
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G4double rand = G4UniformRand()*cdf[nBins-1];
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G4int ibin = 0;
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while (rand > cdf[ibin]) ibin++;
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G4double x = nBins;
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if (ibin < nBins) {
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lowerBinEdge = ibin;
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upperBinEdge = ibin+1;
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x = sampleSlopedLine();
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}
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return x/nBins;
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}
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G4double G4BetaSpectrumSampler::sampleSlopedLine()
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{
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G4double x;
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G4double rand = G4UniformRand();
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ylower = pdf[lowerBinEdge];
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yupper = pdf[upperBinEdge];
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if (std::abs(2.*(yupper - ylower)/(yupper + ylower) ) < 1.E-6) {
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// Slope is near zero, sample flat
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x = lowerBinEdge + rand*(upperBinEdge - lowerBinEdge);
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} else {
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// Sample incline
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x = (yupper*lowerBinEdge - ylower*upperBinEdge +
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std::sqrt(ylower*ylower + rand*(yupper*yupper - ylower*ylower) ) )
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/(yupper - ylower);
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}
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return x;
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}
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