Gabriele Cosmo
216 lines
7.2 KiB
C++
216 lines
7.2 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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//
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// $Id: G4RKG3_Stepper.cc 68055 2013-03-13 14:43:28Z gcosmo $
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//
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// -------------------------------------------------------------------
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#include "G4RKG3_Stepper.hh"
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#include "G4LineSection.hh"
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#include "G4Mag_EqRhs.hh"
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G4RKG3_Stepper::G4RKG3_Stepper(G4Mag_EqRhs *EqRhs)
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: G4MagIntegratorStepper(EqRhs,6), hStep(0.)
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{
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}
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G4RKG3_Stepper::~G4RKG3_Stepper()
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{
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}
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void G4RKG3_Stepper::Stepper( const G4double yInput[8],
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const G4double dydx[6],
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G4double Step,
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G4double yOut[8],
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G4double yErr[])
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{
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G4double B[3];
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G4int nvar = 6 ;
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G4int i;
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G4double by15 = 1. / 15. ; // was 0.066666666 ;
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G4double yTemp[8], dydxTemp[6], yIn[8] ;
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// Saving yInput because yInput and yOut can be aliases for same array
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for(i=0;i<nvar;i++) yIn[i]=yInput[i];
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yIn[6] = yInput[6];
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yIn[7] = yInput[7];
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G4double h = Step * 0.5;
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hStep=Step;
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// Do two half steps
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StepNoErr(yIn, dydx,h, yTemp,B) ;
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//Store Bfld for DistChord Calculation
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for(i=0;i<3;i++)BfldIn[i]=B[i];
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// RightHandSide(yTemp,dydxTemp) ;
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GetEquationOfMotion()->EvaluateRhsGivenB(yTemp,B,dydxTemp) ;
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StepNoErr(yTemp,dydxTemp,h,yOut,B);
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// Store midpoint, chord calculation
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fyMidPoint = G4ThreeVector( yTemp[0], yTemp[1], yTemp[2]);
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// Do a full Step
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h *= 2 ;
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StepNoErr(yIn,dydx,h,yTemp,B);
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for(i=0;i<nvar;i++)
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{
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yErr[i] = yOut[i] - yTemp[i] ;
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yOut[i] += yErr[i]*by15 ; // Provides 5th order of accuracy
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}
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//Store values for DistChord method
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fyInitial = G4ThreeVector( yIn[0], yIn[1], yIn[2]);
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fpInitial = G4ThreeVector( yIn[3], yIn[4], yIn[5]);
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fyFinal = G4ThreeVector( yOut[0], yOut[1], yOut[2]);
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// NormaliseTangentVector( yOut ); // Deleted
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}
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// ---------------------------------------------------------------------------
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// Integrator for RK from G3 with evaluation of error in solution and delta
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// geometry based on naive similarity with the case of uniform magnetic field.
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// B1[3] is input and is the first magnetic field values
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// B2[3] is output and is the final magnetic field values.
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void G4RKG3_Stepper::StepWithEst( const G4double*,
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const G4double*,
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G4double,
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G4double*,
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G4double&,
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G4double&,
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const G4double*,
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G4double* )
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{
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G4Exception("G4RKG3_Stepper::StepWithEst()", "GeomField0001",
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FatalException, "Method no longer used.");
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}
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// -----------------------------------------------------------------
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// Integrator RK Stepper from G3 with only two field evaluation per Step.
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// It is used in propagation initial Step by small substeps after solution
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// error and delta geometry considerations. B[3] is magnetic field which
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// is passed from substep to substep.
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void G4RKG3_Stepper::StepNoErr(const G4double tIn[8],
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const G4double dydx[6],
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G4double Step,
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G4double tOut[8],
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G4double B[3] ) // const
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{
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// Copy and edit the routine above, to delete alpha2, beta2, ...
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G4double K1[7],K2[7],K3[7],K4[7] ;
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G4double tTemp[8], yderiv[6] ;
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// Need Momentum value to give correct values to the coefficients in equation
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// Integration on unit velocity, but tIn[3,4,5] is momentum
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G4double mom,inverse_mom;
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G4int i ;
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const G4double c1=0.5,c2=0.125,c3=1./6.;
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// GetEquationOfMotion()->EvaluateRhsReturnB(tIn,dydx,B1) ;
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// Correction for momentum not a velocity
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// Need the protection !!! must be not zero
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mom=std::sqrt(tIn[3]*tIn[3]+tIn[4]*tIn[4]+tIn[5]*tIn[5]);
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inverse_mom=1./mom;
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for(i=0;i<3;i++)
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{
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K1[i] = Step * dydx[i+3]*inverse_mom;
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tTemp[i] = tIn[i] + Step*(c1*tIn[i+3]*inverse_mom + c2*K1[i]) ;
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tTemp[i+3] = tIn[i+3] + c1*K1[i]*mom ;
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}
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GetEquationOfMotion()->EvaluateRhsReturnB(tTemp,yderiv,B) ;
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for(i=0;i<3;i++)
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{
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K2[i] = Step * yderiv[i+3]*inverse_mom;
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tTemp[i+3] = tIn[i+3] + c1*K2[i]*mom ;
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}
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// Given B, calculate yderiv !
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GetEquationOfMotion()->EvaluateRhsGivenB(tTemp,B,yderiv) ;
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for(i=0;i<3;i++)
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{
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K3[i] = Step * yderiv[i+3]*inverse_mom;
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tTemp[i] = tIn[i] + Step*(tIn[i+3]*inverse_mom + c1*K3[i]) ;
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tTemp[i+3] = tIn[i+3] + K3[i]*mom ;
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}
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// Calculates y-deriv(atives) & returns B too!
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GetEquationOfMotion()->EvaluateRhsReturnB(tTemp,yderiv,B) ;
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for(i=0;i<3;i++) // Output trajectory vector
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{
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K4[i] = Step * yderiv[i+3]*inverse_mom;
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tOut[i] = tIn[i] + Step*(tIn[i+3]*inverse_mom+ (K1[i] + K2[i] + K3[i])*c3) ;
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tOut[i+3] = tIn[i+3] + mom*(K1[i] + 2*K2[i] + 2*K3[i] +K4[i])*c3 ;
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}
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tOut[6] = tIn[6];
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tOut[7] = tIn[7];
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// NormaliseTangentVector( tOut );
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}
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// ---------------------------------------------------------------------------
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G4double G4RKG3_Stepper::DistChord() const
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{
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// Soon: must check whether h/R > 2 pi !!
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// Method below is good only for < 2 pi
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G4double distChord,distLine;
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if (fyInitial != fyFinal) {
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distLine= G4LineSection::Distline(fyMidPoint,fyInitial,fyFinal );
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distChord = distLine;
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}else{
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distChord = (fyMidPoint-fyInitial).mag();
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}
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return distChord;
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}
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