Gabriele Cosmo
230 lines
8.0 KiB
C++
230 lines
8.0 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: G4ConstRK4.cc 66356 2012-12-18 09:02:32Z gcosmo $
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//
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//
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// - 18.09.2008 - J.Apostolakis, T.Nikitina - Created
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// -------------------------------------------------------------------
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#include "G4ConstRK4.hh"
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#include "G4ThreeVector.hh"
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#include "G4LineSection.hh"
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//////////////////////////////////////////////////////////////////
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//
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// Constructor sets the number of *State* variables (default = 8)
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// The number of variables integrated is always 6
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G4ConstRK4::G4ConstRK4(G4Mag_EqRhs* EqRhs, G4int numStateVariables)
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: G4MagErrorStepper(EqRhs, 6, numStateVariables)
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{
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// const G4int numberOfVariables= 6;
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if( numStateVariables < 8 )
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{
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std::ostringstream message;
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message << "The number of State variables at least 8 " << G4endl
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<< "Instead it is - numStateVariables= " << numStateVariables;
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G4Exception("G4ConstRK4::G4ConstRK4()", "GeomField0002",
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FatalException, message, "Use another Stepper!");
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}
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fEq = EqRhs;
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yMiddle = new G4double[8];
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dydxMid = new G4double[8];
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yInitial = new G4double[8];
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yOneStep = new G4double[8];
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dydxm = new G4double[8];
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dydxt = new G4double[8];
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yt = new G4double[8];
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Field[0]=0.; Field[1]=0.; Field[2]=0.;
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}
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////////////////////////////////////////////////////////////////
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//
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// Destructor
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G4ConstRK4::~G4ConstRK4()
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{
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delete [] yMiddle;
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delete [] dydxMid;
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delete [] yInitial;
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delete [] yOneStep;
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delete [] dydxm;
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delete [] dydxt;
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delete [] yt;
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}
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//////////////////////////////////////////////////////////////////////
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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, use the classical 4th Runge-Kutta
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// method to advance the solution over an interval h and return the
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// incremented variables as yout[0,...,n-1], which is not a distinct
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// array from y. The user supplies the routine RightHandSide(x,y,dydx),
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// which returns derivatives dydx at x. The source is routine rk4 from
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// NRC p. 712-713 .
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void G4ConstRK4::DumbStepper( const G4double yIn[],
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const G4double dydx[],
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G4double h,
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G4double yOut[])
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{
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G4double hh = h*0.5 , h6 = h/6.0 ;
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// 1st Step K1=h*dydx
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yt[5] = yIn[5] + hh*dydx[5] ;
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yt[4] = yIn[4] + hh*dydx[4] ;
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yt[3] = yIn[3] + hh*dydx[3] ;
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yt[2] = yIn[2] + hh*dydx[2] ;
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yt[1] = yIn[1] + hh*dydx[1] ;
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yt[0] = yIn[0] + hh*dydx[0] ;
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RightHandSideConst(yt,dydxt) ;
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// 2nd Step K2=h*dydxt
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yt[5] = yIn[5] + hh*dydxt[5] ;
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yt[4] = yIn[4] + hh*dydxt[4] ;
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yt[3] = yIn[3] + hh*dydxt[3] ;
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yt[2] = yIn[2] + hh*dydxt[2] ;
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yt[1] = yIn[1] + hh*dydxt[1] ;
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yt[0] = yIn[0] + hh*dydxt[0] ;
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RightHandSideConst(yt,dydxm) ;
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// 3rd Step K3=h*dydxm
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// now dydxm=(K2+K3)/h
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yt[5] = yIn[5] + h*dydxm[5] ;
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dydxm[5] += dydxt[5] ;
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yt[4] = yIn[4] + h*dydxm[4] ;
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dydxm[4] += dydxt[4] ;
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yt[3] = yIn[3] + h*dydxm[3] ;
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dydxm[3] += dydxt[3] ;
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yt[2] = yIn[2] + h*dydxm[2] ;
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dydxm[2] += dydxt[2] ;
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yt[1] = yIn[1] + h*dydxm[1] ;
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dydxm[1] += dydxt[1] ;
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yt[0] = yIn[0] + h*dydxm[0] ;
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dydxm[0] += dydxt[0] ;
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RightHandSideConst(yt,dydxt) ;
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// 4th Step K4=h*dydxt
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yOut[5] = yIn[5]+h6*(dydx[5]+dydxt[5]+2.0*dydxm[5]);
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yOut[4] = yIn[4]+h6*(dydx[4]+dydxt[4]+2.0*dydxm[4]);
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yOut[3] = yIn[3]+h6*(dydx[3]+dydxt[3]+2.0*dydxm[3]);
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yOut[2] = yIn[2]+h6*(dydx[2]+dydxt[2]+2.0*dydxm[2]);
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yOut[1] = yIn[1]+h6*(dydx[1]+dydxt[1]+2.0*dydxm[1]);
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yOut[0] = yIn[0]+h6*(dydx[0]+dydxt[0]+2.0*dydxm[0]);
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} // end of DumbStepper ....................................................
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////////////////////////////////////////////////////////////////
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//
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// Stepper
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void
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G4ConstRK4::Stepper( const G4double yInput[],
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const G4double dydx[],
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G4double hstep,
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G4double yOutput[],
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G4double yError [] )
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{
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const G4int nvar = 6; // number of variables integrated
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const G4int maxvar= GetNumberOfStateVariables();
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// Correction for Richardson extrapolation
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G4double correction = 1. / ( (1 << IntegratorOrder()) -1 );
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G4int i;
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// Saving yInput because yInput and yOutput can be aliases for same array
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for (i=0; i<maxvar; i++) { yInitial[i]= yInput[i]; }
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// Must copy the part of the state *not* integrated to the output
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for (i=nvar; i<maxvar; i++) { yOutput[i]= yInput[i]; }
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// yInitial[7]= yInput[7]; // The time is typically needed
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yMiddle[7] = yInput[7]; // Copy the time from initial value
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yOneStep[7] = yInput[7]; // As it contributes to final value of yOutput ?
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// yOutput[7] = yInput[7]; // -> dumb stepper does it too for RK4
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yError[7] = 0.0;
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G4double halfStep = hstep * 0.5;
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// Do two half steps
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//
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GetConstField(yInitial,Field);
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DumbStepper (yInitial, dydx, halfStep, yMiddle);
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RightHandSideConst(yMiddle, dydxMid);
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DumbStepper (yMiddle, dydxMid, halfStep, yOutput);
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// Store midpoint, chord calculation
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//
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fMidPoint = G4ThreeVector( yMiddle[0], yMiddle[1], yMiddle[2]);
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// Do a full Step
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//
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DumbStepper(yInitial, dydx, hstep, yOneStep);
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for(i=0;i<nvar;i++)
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{
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yError [i] = yOutput[i] - yOneStep[i] ;
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yOutput[i] += yError[i]*correction ;
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// Provides accuracy increased by 1 order via the
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// Richardson extrapolation
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}
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fInitialPoint = G4ThreeVector( yInitial[0], yInitial[1], yInitial[2]);
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fFinalPoint = G4ThreeVector( yOutput[0], yOutput[1], yOutput[2]);
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return;
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}
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////////////////////////////////////////////////////////////////
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//
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// Estimate the maximum distance from the curve to the chord
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//
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// We estimate this using the distance of the midpoint to chord.
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// The method below is good only for angle deviations < 2 pi;
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// this restriction should not be a problem for the Runge Kutta methods,
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// which generally cannot integrate accurately for large angle deviations
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G4double G4ConstRK4::DistChord() const
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{
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G4double distLine, distChord;
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if (fInitialPoint != fFinalPoint)
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{
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distLine= G4LineSection::Distline( fMidPoint, fInitialPoint, fFinalPoint );
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// This is a class method that gives distance of Mid
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// from the Chord between the Initial and Final points
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distChord = distLine;
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}
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else
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{
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distChord = (fMidPoint-fInitialPoint).mag();
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}
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return distChord;
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}
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