G4GaussChebyshevQ.cc

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//
// G4GaussChebyshevQ class implementation
//
// Author: V.Grichine, 13.05.1997
// --------------------------------------------------------------------
 
#include "G4GaussChebyshevQ.hh"
#include "G4PhysicalConstants.hh"
 
// -----------------------------------------------------
//
// Constructor for Gauss-Chebyshev quadrature method
//
G4GaussChebyshevQ::G4GaussChebyshevQ(function pFunction, G4int nChebyshev)
  : G4VGaussianQuadrature(pFunction)
{
  fNumber      = nChebyshev;  // Try to reduce fNumber twice ??
  G4double cof = pi / fNumber;
  fAbscissa    = new G4double[fNumber];
  fWeight      = new G4double[fNumber];
  for(G4int i = 0; i < fNumber; ++i)
  {
    fAbscissa[i] = std::cos(cof * (i + 0.5));
    fWeight[i]   = cof * std::sqrt(1 - fAbscissa[i] * fAbscissa[i]);
  }
}
 
// -------------------------------------------------------------------------------
//
// Integrates function pointed by fFunction from a to b by Gauss-Chebyshev
// quadrature method
//
G4double G4GaussChebyshevQ::Integral(G4double a, G4double b) const
{
  G4double xDiff = 0.5 * (b - a), xMean = 0.5 * (a + b), dx = 0.0,
           integral = 0.0;
 
  for(G4int i = 0; i < fNumber; ++i)
  {
    dx = xDiff * fAbscissa[i];
    integral += fWeight[i] * fFunction(xMean + dx);
  }
  return integral *= xDiff;
}