Gabriele Cosmo
182 lines
6.9 KiB
C++
182 lines
6.9 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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// G4ConstRK4
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//
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// Class description:
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//
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// G4ConstRK4 performs the integration of one step with error calculation
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// in constant magnetic field. The integration method is the same as in
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// ClassicalRK4. The field value is assumed constant for the step.
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// This field evaluation is called only once per step.
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// G4ConstRK4 can be used only for magnetic fields.
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// Authors: J.Apostolakis, T.Nikitina (CERN), 18.09.2008
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// -------------------------------------------------------------------
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#ifndef G4CONSTRK4_HH
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#define G4CONSTRK4_HH
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#include "G4MagErrorStepper.hh"
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#include "G4EquationOfMotion.hh"
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#include "G4Mag_EqRhs.hh"
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/**
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* @brief G4ConstRK4 performs the integration of one step with error
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* calculation in constant magnetic field. The integration method is the
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* same as in ClassicalRK4. The field value is assumed constant for the step.
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* This field evaluation is called only once per step.
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* G4ConstRK4 can be used only for magnetic fields.
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*/
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class G4ConstRK4 : public G4MagErrorStepper
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{
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public:
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/**
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* Constructor for G4ConstRK4.
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* @param[in] EqRhs Pointer to the provided equation of motion.
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* @param[in] numberOfVariables The number of integration variables.
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*/
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G4ConstRK4(G4Mag_EqRhs* EquationMotion,
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G4int numberOfStateVariables=8);
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/**
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* Destructor.
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*/
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~G4ConstRK4() override;
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/**
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* Copy constructor and assignment operator not allowed.
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*/
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G4ConstRK4(const G4ConstRK4&) = delete;
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G4ConstRK4& operator=(const G4ConstRK4&) = delete;
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/**
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* The stepper for the Runge Kutta integration.
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* The stepsize is fixed, with the step size given by 'h'.
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* Integrates ODE starting values y[0 to 6].
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* Outputs yout[] and its estimated error yerr[].
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* @param[in] y Starting values array of integration variables.
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* @param[in] dydx Derivatives array.
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* @param[in] h The given step size.
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* @param[out] yout Integration output.
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* @param[out] yerr The estimated error.
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*/
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void Stepper( const G4double y[],
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const G4double dydx[],
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G4double h,
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G4double yout[],
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G4double yerr[] ) override;
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/**
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* Given values for the variables y[0,..,n-1] and their derivatives
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* dydx[0,...,n-1] known at x, uses the classical 4th Runge-Kutta
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* method to advance the solution over an interval h and returns the
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* incremented variables as yout[0,...,n-1]. The user supplies the
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* function RightHandSide(x,y,dydx), which returns derivatives dydx at x.
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* The source is routine rk4 from NRC p.712-713.
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* @param[in] y Starting values array of integration variables.
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* @param[in] dydx Derivatives array.
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* @param[in] h The given step size.
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* @param[out] yout Integration output.
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*/
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void DumbStepper( const G4double yIn[],
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const G4double dydx[],
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G4double h,
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G4double yOut[] ) override ;
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/**
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* Returns the distance from chord line.
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*/
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G4double DistChord() const override;
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/**
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* Returns the derivatives value, at position and time 'y'.
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* @param[in] y The position vector plus time (x,y,z,t).
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* @param[out] dydx The derivatives array.
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*/
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inline void RightHandSideConst(const G4double y[], G4double dydx[] ) const;
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/**
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* Returns the field values, at position and time 'y'.
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* @param[in] y The position vector plus time (x,y,z,t).
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* @param[out] Field The field value in output.
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*/
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inline void GetConstField(const G4double y[], G4double Field[]);
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/**
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* Returns the order, 4, of integration.
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*/
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inline G4int IntegratorOrder() const override { return 4; }
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/**
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* Returns the stepper type-ID, "kConstRK4".
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*/
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inline G4StepperType StepperType() const override { return kConstRK4; }
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private:
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G4ThreeVector fInitialPoint, fMidPoint, fFinalPoint;
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// Data stored in order to find the chord
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G4double *dydxm, *dydxt, *yt; // scratch space - not state
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G4double *yInitial, *yMiddle, *dydxMid, *yOneStep;
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G4Mag_EqRhs* fEq = nullptr;
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G4double Field[3];
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};
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// Inline methods
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inline void G4ConstRK4::RightHandSideConst(const G4double y[],
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G4double dydx[] ) const
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{
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G4double momentum_mag_square = y[3]*y[3] + y[4]*y[4] + y[5]*y[5];
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G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
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G4double cof = fEq->FCof()*inv_momentum_magnitude;
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dydx[0] = y[3]*inv_momentum_magnitude; // (d/ds)x = Vx/V
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dydx[1] = y[4]*inv_momentum_magnitude; // (d/ds)y = Vy/V
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dydx[2] = y[5]*inv_momentum_magnitude; // (d/ds)z = Vz/V
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dydx[3] = cof*(y[4]*Field[2] - y[5]*Field[1]) ; // Ax = a*(Vy*Bz - Vz*By)
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dydx[4] = cof*(y[5]*Field[0] - y[3]*Field[2]) ; // Ay = a*(Vz*Bx - Vx*Bz)
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dydx[5] = cof*(y[3]*Field[1] - y[4]*Field[0]) ; // Az = a*(Vx*By - Vy*Bx)
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}
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inline void G4ConstRK4::GetConstField(const G4double y[], G4double B[])
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{
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G4double PositionAndTime[4];
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PositionAndTime[0] = y[0];
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PositionAndTime[1] = y[1];
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PositionAndTime[2] = y[2];
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// Global Time
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PositionAndTime[3] = y[7];
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fEq -> GetFieldValue(PositionAndTime, B);
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}
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#endif
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