Gabriele Cosmo
125 lines
4.7 KiB
C++
125 lines
4.7 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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// G4CashKarpRKF45
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//
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// Class description:
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//
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// The Cash-Karp Runge-Kutta-Fehlberg 4/5 method is an embedded fourth
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// order method (giving fifth-order accuracy) for the solution of an ODE.
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// Two different fourth order estimates are calculated; their difference
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// gives an error estimate. [ref. Numerical Recipes in C, 2nd Edition]
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// It is used to integrate the equations of the motion of a particle
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// in a magnetic field.
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// Authors: J.Apostolakis, V.Grichine (CERN), 30.01.1997
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// -------------------------------------------------------------------
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#ifndef G4CASHKARP_RKF45_HH
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#define G4CASHKARP_RKF45_HH
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#include "G4MagIntegratorStepper.hh"
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/**
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* @brief G4CashKarpRKF45 implements the Cash-Karp Runge-Kutta-Fehlberg
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* 4/5 method, an embedded fourth order method (giving fifth-order accuracy)
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* for the solution of an ODE. Two different fourth order estimates are
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* calculated; their difference gives an error estimate.
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* It is used to integrate the equations of the motion of a particle
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* in a magnetic field.
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*/
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class G4CashKarpRKF45 : public G4MagIntegratorStepper
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{
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public:
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/**
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* Constructor for G4CashKarpRKF45.
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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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* @param[in] primary Flag for initialisation of the auxiliary stepper.
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*/
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G4CashKarpRKF45( G4EquationOfMotion* EqRhs,
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G4int numberOfVariables = 6,
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G4bool primary = true );
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/**
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* Destructor.
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*/
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~G4CashKarpRKF45() override;
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/**
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* Copy constructor and assignment operator not allowed.
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*/
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G4CashKarpRKF45(const G4CashKarpRKF45&) = delete;
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G4CashKarpRKF45& operator=(const G4CashKarpRKF45&) = 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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* 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 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, "kCashKarpRKF45".
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*/
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inline G4StepperType StepperType() const override { return kCashKarpRKF45; }
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private:
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/** Scratch space. */
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G4double *ak2, *ak3, *ak4, *ak5, *ak6, *yTemp, *yIn;
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G4double fLastStepLength = 0.0;
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/** For DistChord calculations. */
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G4double *fLastInitialVector, *fLastFinalVector,
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*fLastDyDx, *fMidVector, *fMidError;
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G4CashKarpRKF45* fAuxStepper = nullptr;
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};
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#endif
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