RK4OneStepTempl.h

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#ifndef RK4OneStepTempl_H
#define RK4OneStepTempl_H

#include "FWCore/Utilities/interface/Visibility.h"
#include "RKSmallVector.h"
#include "RKDerivative.h"

template <typename T, int N>
class dso_internal RK4OneStepTempl {
public:
  typedef T Scalar;
  typedef RKSmallVector<T, N> Vector;

  Vector operator()(Scalar startPar, const Vector& startState, const RKDerivative<T, N>& deriv, Scalar step) const {
    // cout << "RK4OneStepTempl: starting from " << startPar << startState << endl;

    Vector k1 = step * deriv(startPar, startState);
    Vector k2 = step * deriv(startPar + step / 2, startState + k1 / 2);
    Vector k3 = step * deriv(startPar + step / 2, startState + k2 / 2);
    Vector k4 = step * deriv(startPar + step, startState + k3);

    Vector result = startState + k1 / 6 + k2 / 3 + k3 / 3 + k4 / 6;

    // cout << "RK4OneStepTempl: result for step " << step << " is " << result << endl;

    return result;
  }
};

#endif