TrkExtrapolation/TrkExUtils/TrkExUtils/RealQuadraticEquation.h

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/*
  Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
*/
 
// RealQuadraticEquation.h, (c) ATLAS Detector software
 
#ifndef TRKEXUTILS_REALQUADRATICEQUATION_H
#define TRKEXUTILS_REALQUADRATICEQUATION_H
 
#include <cmath>
#include <utility>
 
namespace Trk {
enum RQESolutionType
{
  none = 0,
  one = 1,
  two = 2
};
 
struct RealQuadraticEquation
{
 
  double first;
  double second;
  RQESolutionType solutions;
 
  RealQuadraticEquation(double alpha, double beta, double gamma)
    : first{}
    , second{}
  {
    double discriminant = beta * beta - 4 * alpha * gamma;
    if (discriminant < 0)
      solutions = none;
    else {
      solutions = (discriminant == 0) ? one : two;
      double q =
        -0.5 * (beta + (beta > 0 ? sqrt(discriminant) : -sqrt(discriminant)));
      first = q / alpha;
      second = gamma / q;
    }
  }
};
 
} // end of namespace
 
#endif //  TRKEXUTILS_REALQUADRATICEQUATION_H